linux/drivers/cpufreq/cpufreq_governor.c

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/*
* drivers/cpufreq/cpufreq_governor.c
*
* CPUFREQ governors common code
*
* Copyright (C) 2001 Russell King
* (C) 2003 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>.
* (C) 2003 Jun Nakajima <jun.nakajima@intel.com>
* (C) 2009 Alexander Clouter <alex@digriz.org.uk>
* (c) 2012 Viresh Kumar <viresh.kumar@linaro.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/export.h>
#include <linux/kernel_stat.h>
#include <linux/slab.h>
#include "cpufreq_governor.h"
static struct attribute_group *get_sysfs_attr(struct dbs_data *dbs_data)
{
if (have_governor_per_policy())
return dbs_data->cdata->attr_group_gov_pol;
else
return dbs_data->cdata->attr_group_gov_sys;
}
void dbs_check_cpu(struct dbs_data *dbs_data, int cpu)
{
struct cpu_dbs_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
struct od_dbs_tuners *od_tuners = dbs_data->tuners;
struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
struct cpufreq_policy *policy = cdbs->shared->policy;
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
unsigned int sampling_rate;
unsigned int max_load = 0;
unsigned int ignore_nice;
unsigned int j;
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
if (dbs_data->cdata->governor == GOV_ONDEMAND) {
struct od_cpu_dbs_info_s *od_dbs_info =
dbs_data->cdata->get_cpu_dbs_info_s(cpu);
/*
* Sometimes, the ondemand governor uses an additional
* multiplier to give long delays. So apply this multiplier to
* the 'sampling_rate', so as to keep the wake-up-from-idle
* detection logic a bit conservative.
*/
sampling_rate = od_tuners->sampling_rate;
sampling_rate *= od_dbs_info->rate_mult;
ignore_nice = od_tuners->ignore_nice_load;
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
} else {
sampling_rate = cs_tuners->sampling_rate;
ignore_nice = cs_tuners->ignore_nice_load;
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
}
cpufreq: ondemand: Change the calculation of target frequency The ondemand governor calculates load in terms of frequency and increases it only if load_freq is greater than up_threshold multiplied by the current or average frequency. This appears to produce oscillations of frequency between min and max because, for example, a relatively small load can easily saturate minimum frequency and lead the CPU to the max. Then, it will decrease back to the min due to small load_freq. Change the calculation method of load and target frequency on the basis of the following two observations: - Load computation should not depend on the current or average measured frequency. For example, absolute load of 80% at 100MHz is not necessarily equivalent to 8% at 1000MHz in the next sampling interval. - It should be possible to increase the target frequency to any value present in the frequency table proportional to the absolute load, rather than to the max only, so that: Target frequency = C * load where we take C = policy->cpuinfo.max_freq / 100. Tested on Intel i7-3770 CPU @ 3.40GHz and on Quad core 1500MHz Krait. Phoronix benchmark of Linux Kernel Compilation 3.1 test shows an increase ~1.5% in performance. cpufreq_stats (time_in_state) shows that middle frequencies are used more, with this patch. Highest and lowest frequencies were used less by ~9%. [rjw: We have run multiple other tests on kernels with this change applied and in the vast majority of cases it turns out that the resulting performance improvement also leads to reduced consumption of energy. The change is additionally justified by the overall simplification of the code in question.] Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2013-06-05 16:01:25 +00:00
/* Get Absolute Load */
for_each_cpu(j, policy->cpus) {
struct cpu_dbs_info *j_cdbs;
u64 cur_wall_time, cur_idle_time;
unsigned int idle_time, wall_time;
unsigned int load;
int io_busy = 0;
j_cdbs = dbs_data->cdata->get_cpu_cdbs(j);
/*
* For the purpose of ondemand, waiting for disk IO is
* an indication that you're performance critical, and
* not that the system is actually idle. So do not add
* the iowait time to the cpu idle time.
*/
if (dbs_data->cdata->governor == GOV_ONDEMAND)
io_busy = od_tuners->io_is_busy;
cur_idle_time = get_cpu_idle_time(j, &cur_wall_time, io_busy);
wall_time = (unsigned int)
(cur_wall_time - j_cdbs->prev_cpu_wall);
j_cdbs->prev_cpu_wall = cur_wall_time;
cpufreq: governor: Fix negative idle_time when configured with CONFIG_HZ_PERIODIC It is reported that, with CONFIG_HZ_PERIODIC=y cpu stays at the lowest frequency even if the usage goes to 100%, neither ondemand nor conservative governor works, however performance and userspace work as expected. If set with CONFIG_NO_HZ_FULL=y, everything goes well. This problem is caused by improper calculation of the idle_time when the load is extremely high(near 100%). Firstly, cpufreq_governor uses get_cpu_idle_time to get the total idle time for specific cpu, then: 1.If the system is configured with CONFIG_NO_HZ_FULL, the idle time is returned by ktime_get, which is always increasing, it's OK. 2.However, if the system is configured with CONFIG_HZ_PERIODIC, get_cpu_idle_time might not guarantee to be always increasing, because it will leverage get_cpu_idle_time_jiffy to calculate the idle_time, consider the following scenario: At T1: idle_tick_1 = total_tick_1 - user_tick_1 sample period(80ms)... At T2: ( T2 = T1 + 80ms): idle_tick_2 = total_tick_2 - user_tick_2 Currently the algorithm is using (idle_tick_2 - idle_tick_1) to get the delta idle_time during the past sample period, however it CAN NOT guarantee that idle_tick_2 >= idle_tick_1, especially when cpu load is high. (Yes, total_tick_2 >= total_tick_1, and user_tick_2 >= user_tick_1, but how about idle_tick_2 and idle_tick_1? No guarantee.) So governor might get a negative value of idle_time during the past sample period, which might mislead the system that the idle time is very big(converted to unsigned int), and the busy time is nearly zero, which causes the governor to always choose the lowest cpufreq, then cause this problem. In theory there are two solutions: 1.The logic should not rely on the idle tick during every sample period, but be based on the busy tick directly, as this is how 'top' is implemented. 2.Or the logic must make sure that the idle_time is strictly increasing during each sample period, then there would be no negative idle_time anymore. This solution requires minimum modification to current code and this patch uses method 2. Link: https://bugzilla.kernel.org/show_bug.cgi?id=69821 Reported-by: Jan Fikar <j.fikar@gmail.com> Signed-off-by: Chen Yu <yu.c.chen@intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-16 04:20:29 +00:00
if (cur_idle_time < j_cdbs->prev_cpu_idle)
cur_idle_time = j_cdbs->prev_cpu_idle;
idle_time = (unsigned int)
(cur_idle_time - j_cdbs->prev_cpu_idle);
j_cdbs->prev_cpu_idle = cur_idle_time;
if (ignore_nice) {
u64 cur_nice;
unsigned long cur_nice_jiffies;
cur_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE] -
cdbs->prev_cpu_nice;
/*
* Assumption: nice time between sampling periods will
* be less than 2^32 jiffies for 32 bit sys
*/
cur_nice_jiffies = (unsigned long)
cputime64_to_jiffies64(cur_nice);
cdbs->prev_cpu_nice =
kcpustat_cpu(j).cpustat[CPUTIME_NICE];
idle_time += jiffies_to_usecs(cur_nice_jiffies);
}
if (unlikely(!wall_time || wall_time < idle_time))
continue;
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
/*
* If the CPU had gone completely idle, and a task just woke up
* on this CPU now, it would be unfair to calculate 'load' the
* usual way for this elapsed time-window, because it will show
* near-zero load, irrespective of how CPU intensive that task
* actually is. This is undesirable for latency-sensitive bursty
* workloads.
*
* To avoid this, we reuse the 'load' from the previous
* time-window and give this task a chance to start with a
* reasonably high CPU frequency. (However, we shouldn't over-do
* this copy, lest we get stuck at a high load (high frequency)
* for too long, even when the current system load has actually
* dropped down. So we perform the copy only once, upon the
* first wake-up from idle.)
*
* Detecting this situation is easy: the governor's utilization
* update handler would not have run during CPU-idle periods.
* Hence, an unusually large 'wall_time' (as compared to the
* sampling rate) indicates this scenario.
2014-06-09 08:51:24 +00:00
*
* prev_load can be zero in two cases and we must recalculate it
* for both cases:
* - during long idle intervals
* - explicitly set to zero
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
*/
2014-06-09 08:51:24 +00:00
if (unlikely(wall_time > (2 * sampling_rate) &&
j_cdbs->prev_load)) {
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
load = j_cdbs->prev_load;
2014-06-09 08:51:24 +00:00
/*
* Perform a destructive copy, to ensure that we copy
* the previous load only once, upon the first wake-up
* from idle.
*/
j_cdbs->prev_load = 0;
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
} else {
load = 100 * (wall_time - idle_time) / wall_time;
j_cdbs->prev_load = load;
}
if (load > max_load)
max_load = load;
}
dbs_data->cdata->gov_check_cpu(cpu, max_load);
}
EXPORT_SYMBOL_GPL(dbs_check_cpu);
void gov_set_update_util(struct cpu_common_dbs_info *shared,
unsigned int delay_us)
{
struct cpufreq_policy *policy = shared->policy;
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
struct dbs_data *dbs_data = policy->governor_data;
int cpu;
gov_update_sample_delay(shared, delay_us);
shared->last_sample_time = 0;
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
for_each_cpu(cpu, policy->cpus) {
struct cpu_dbs_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
cpufreq_set_update_util_data(cpu, &cdbs->update_util);
}
}
EXPORT_SYMBOL_GPL(gov_set_update_util);
static inline void gov_clear_update_util(struct cpufreq_policy *policy)
{
int i;
for_each_cpu(i, policy->cpus)
cpufreq_set_update_util_data(i, NULL);
synchronize_rcu();
}
static void gov_cancel_work(struct cpu_common_dbs_info *shared)
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
{
/* Tell dbs_update_util_handler() to skip queuing up work items. */
atomic_inc(&shared->skip_work);
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
/*
* If dbs_update_util_handler() is already running, it may not notice
* the incremented skip_work, so wait for it to complete to prevent its
* work item from being queued up after the cancel_work_sync() below.
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
*/
gov_clear_update_util(shared->policy);
irq_work_sync(&shared->irq_work);
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
cancel_work_sync(&shared->work);
atomic_set(&shared->skip_work, 0);
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
}
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
static void dbs_work_handler(struct work_struct *work)
{
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
struct cpu_common_dbs_info *shared = container_of(work, struct
cpu_common_dbs_info, work);
struct cpufreq_policy *policy;
struct dbs_data *dbs_data;
unsigned int delay;
policy = shared->policy;
dbs_data = policy->governor_data;
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
/*
* Make sure cpufreq_governor_limits() isn't evaluating load or the
* ondemand governor isn't updating the sampling rate in parallel.
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
*/
mutex_lock(&shared->timer_mutex);
delay = dbs_data->cdata->gov_dbs_timer(policy);
shared->sample_delay_ns = jiffies_to_nsecs(delay);
mutex_unlock(&shared->timer_mutex);
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
/*
* If the atomic operation below is reordered with respect to the
* sample delay modification, the utilization update handler may end
* up using a stale sample delay value.
*/
smp_mb__before_atomic();
atomic_dec(&shared->skip_work);
}
static void dbs_irq_work(struct irq_work *irq_work)
{
struct cpu_common_dbs_info *shared;
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
shared = container_of(irq_work, struct cpu_common_dbs_info, irq_work);
schedule_work(&shared->work);
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
}
static inline void gov_queue_irq_work(struct cpu_common_dbs_info *shared)
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
{
#ifdef CONFIG_SMP
irq_work_queue_on(&shared->irq_work, smp_processor_id());
#else
irq_work_queue(&shared->irq_work);
#endif
}
static void dbs_update_util_handler(struct update_util_data *data, u64 time,
unsigned long util, unsigned long max)
{
struct cpu_dbs_info *cdbs = container_of(data, struct cpu_dbs_info, update_util);
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
struct cpu_common_dbs_info *shared = cdbs->shared;
/*
* The work may not be allowed to be queued up right now.
* Possible reasons:
* - Work has already been queued up or is in progress.
* - The governor is being stopped.
* - It is too early (too little time from the previous sample).
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
*/
if (atomic_inc_return(&shared->skip_work) == 1) {
u64 delta_ns;
delta_ns = time - shared->last_sample_time;
if ((s64)delta_ns >= shared->sample_delay_ns) {
shared->last_sample_time = time;
gov_queue_irq_work(shared);
return;
}
}
atomic_dec(&shared->skip_work);
}
static void set_sampling_rate(struct dbs_data *dbs_data,
unsigned int sampling_rate)
{
if (dbs_data->cdata->governor == GOV_CONSERVATIVE) {
struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
cs_tuners->sampling_rate = sampling_rate;
} else {
struct od_dbs_tuners *od_tuners = dbs_data->tuners;
od_tuners->sampling_rate = sampling_rate;
}
}
static int alloc_common_dbs_info(struct cpufreq_policy *policy,
struct common_dbs_data *cdata)
{
struct cpu_common_dbs_info *shared;
int j;
/* Allocate memory for the common information for policy->cpus */
shared = kzalloc(sizeof(*shared), GFP_KERNEL);
if (!shared)
return -ENOMEM;
/* Set shared for all CPUs, online+offline */
for_each_cpu(j, policy->related_cpus)
cdata->get_cpu_cdbs(j)->shared = shared;
mutex_init(&shared->timer_mutex);
atomic_set(&shared->skip_work, 0);
init_irq_work(&shared->irq_work, dbs_irq_work);
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
INIT_WORK(&shared->work, dbs_work_handler);
return 0;
}
static void free_common_dbs_info(struct cpufreq_policy *policy,
struct common_dbs_data *cdata)
{
struct cpu_dbs_info *cdbs = cdata->get_cpu_cdbs(policy->cpu);
struct cpu_common_dbs_info *shared = cdbs->shared;
int j;
mutex_destroy(&shared->timer_mutex);
for_each_cpu(j, policy->cpus)
cdata->get_cpu_cdbs(j)->shared = NULL;
kfree(shared);
}
static int cpufreq_governor_init(struct cpufreq_policy *policy,
struct dbs_data *dbs_data,
struct common_dbs_data *cdata)
{
unsigned int latency;
int ret;
/* State should be equivalent to EXIT */
if (policy->governor_data)
return -EBUSY;
if (dbs_data) {
if (WARN_ON(have_governor_per_policy()))
return -EINVAL;
ret = alloc_common_dbs_info(policy, cdata);
if (ret)
return ret;
dbs_data->usage_count++;
policy->governor_data = dbs_data;
return 0;
}
dbs_data = kzalloc(sizeof(*dbs_data), GFP_KERNEL);
if (!dbs_data)
return -ENOMEM;
ret = alloc_common_dbs_info(policy, cdata);
if (ret)
goto free_dbs_data;
dbs_data->cdata = cdata;
dbs_data->usage_count = 1;
ret = cdata->init(dbs_data, !policy->governor->initialized);
if (ret)
goto free_common_dbs_info;
/* policy latency is in ns. Convert it to us first */
latency = policy->cpuinfo.transition_latency / 1000;
if (latency == 0)
latency = 1;
/* Bring kernel and HW constraints together */
dbs_data->min_sampling_rate = max(dbs_data->min_sampling_rate,
MIN_LATENCY_MULTIPLIER * latency);
set_sampling_rate(dbs_data, max(dbs_data->min_sampling_rate,
latency * LATENCY_MULTIPLIER));
if (!have_governor_per_policy())
cdata->gdbs_data = dbs_data;
cpufreq: Fix NULL reference crash while accessing policy->governor_data There is a race discovered by Juri, where we are able to: - create and read a sysfs file before policy->governor_data is being set to a non NULL value. OR - set policy->governor_data to NULL, and reading a file before being destroyed. And so such a crash is reported: Unable to handle kernel NULL pointer dereference at virtual address 0000000c pgd = edfc8000 [0000000c] *pgd=bfc8c835 Internal error: Oops: 17 [#1] SMP ARM Modules linked in: CPU: 4 PID: 1730 Comm: cat Not tainted 4.5.0-rc1+ #463 Hardware name: ARM-Versatile Express task: ee8e8480 ti: ee930000 task.ti: ee930000 PC is at show_ignore_nice_load_gov_pol+0x24/0x34 LR is at show+0x4c/0x60 pc : [<c058f1bc>] lr : [<c058ae88>] psr: a0070013 sp : ee931dd0 ip : ee931de0 fp : ee931ddc r10: ee4bc290 r9 : 00001000 r8 : ef2cb000 r7 : ee4bc200 r6 : ef2cb000 r5 : c0af57b0 r4 : ee4bc2e0 r3 : 00000000 r2 : 00000000 r1 : c0928df4 r0 : ef2cb000 Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5387d Table: adfc806a DAC: 00000051 Process cat (pid: 1730, stack limit = 0xee930210) Stack: (0xee931dd0 to 0xee932000) 1dc0: ee931dfc ee931de0 c058ae88 c058f1a4 1de0: edce3bc0 c07bfca4 edce3ac0 00001000 ee931e24 ee931e00 c01fcb90 c058ae48 1e00: 00000001 edce3bc0 00000000 00000001 ee931e50 ee8ff480 ee931e34 ee931e28 1e20: c01fb33c c01fcb0c ee931e8c ee931e38 c01a5210 c01fb314 ee931e9c ee931e48 1e40: 00000000 edce3bf0 befe4a00 ee931f78 00000000 00000000 000001e4 00000000 1e60: c00545a8 edce3ac0 00001000 00001000 befe4a00 ee931f78 00000000 00001000 1e80: ee931ed4 ee931e90 c01fbed8 c01a5038 ed085a58 00020000 00000000 00000000 1ea0: c0ad72e4 ee931f78 ee8ff488 ee8ff480 c077f3fc 00001000 befe4a00 ee931f78 1ec0: 00000000 00001000 ee931f44 ee931ed8 c017c328 c01fbdc4 00001000 00000000 1ee0: ee8ff480 00001000 ee931f44 ee931ef8 c017c65c c03deb10 ee931fac ee931f08 1f00: c0009270 c001f290 c0a8d968 ef2cb000 ef2cb000 ee8ff480 00000020 ee8ff480 1f20: ee8ff480 befe4a00 00001000 ee931f78 00000000 00000000 ee931f74 ee931f48 1f40: c017d1ec c017c2f8 c019c724 c019c684 ee8ff480 ee8ff480 00001000 befe4a00 1f60: 00000000 00000000 ee931fa4 ee931f78 c017d2a8 c017d160 00000000 00000000 1f80: 000a9f20 00001000 befe4a00 00000003 c000ffe4 ee930000 00000000 ee931fa8 1fa0: c000fe40 c017d264 000a9f20 00001000 00000003 befe4a00 00001000 00000000 Unable to handle kernel NULL pointer dereference at virtual address 0000000c 1fc0: 000a9f20 00001000 befe4a00 00000003 00000000 00000000 00000003 00000001 pgd = edfc4000 [0000000c] *pgd=bfcac835 1fe0: 00000000 befe49dc 000197f8 b6e35dfc 60070010 00000003 3065b49d 134ac2c9 [<c058f1bc>] (show_ignore_nice_load_gov_pol) from [<c058ae88>] (show+0x4c/0x60) [<c058ae88>] (show) from [<c01fcb90>] (sysfs_kf_seq_show+0x90/0xfc) [<c01fcb90>] (sysfs_kf_seq_show) from [<c01fb33c>] (kernfs_seq_show+0x34/0x38) [<c01fb33c>] (kernfs_seq_show) from [<c01a5210>] (seq_read+0x1e4/0x4e4) [<c01a5210>] (seq_read) from [<c01fbed8>] (kernfs_fop_read+0x120/0x1a0) [<c01fbed8>] (kernfs_fop_read) from [<c017c328>] (__vfs_read+0x3c/0xe0) [<c017c328>] (__vfs_read) from [<c017d1ec>] (vfs_read+0x98/0x104) [<c017d1ec>] (vfs_read) from [<c017d2a8>] (SyS_read+0x50/0x90) [<c017d2a8>] (SyS_read) from [<c000fe40>] (ret_fast_syscall+0x0/0x1c) Code: e5903044 e1a00001 e3081df4 e34c1092 (e593300c) ---[ end trace 5994b9a5111f35ee ]--- Fix that by making sure, policy->governor_data is updated at the right places only. Cc: 4.2+ <stable@vger.kernel.org> # 4.2+ Reported-and-tested-by: Juri Lelli <juri.lelli@arm.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2016-01-25 17:03:46 +00:00
policy->governor_data = dbs_data;
ret = sysfs_create_group(get_governor_parent_kobj(policy),
get_sysfs_attr(dbs_data));
if (ret)
goto reset_gdbs_data;
return 0;
reset_gdbs_data:
cpufreq: Fix NULL reference crash while accessing policy->governor_data There is a race discovered by Juri, where we are able to: - create and read a sysfs file before policy->governor_data is being set to a non NULL value. OR - set policy->governor_data to NULL, and reading a file before being destroyed. And so such a crash is reported: Unable to handle kernel NULL pointer dereference at virtual address 0000000c pgd = edfc8000 [0000000c] *pgd=bfc8c835 Internal error: Oops: 17 [#1] SMP ARM Modules linked in: CPU: 4 PID: 1730 Comm: cat Not tainted 4.5.0-rc1+ #463 Hardware name: ARM-Versatile Express task: ee8e8480 ti: ee930000 task.ti: ee930000 PC is at show_ignore_nice_load_gov_pol+0x24/0x34 LR is at show+0x4c/0x60 pc : [<c058f1bc>] lr : [<c058ae88>] psr: a0070013 sp : ee931dd0 ip : ee931de0 fp : ee931ddc r10: ee4bc290 r9 : 00001000 r8 : ef2cb000 r7 : ee4bc200 r6 : ef2cb000 r5 : c0af57b0 r4 : ee4bc2e0 r3 : 00000000 r2 : 00000000 r1 : c0928df4 r0 : ef2cb000 Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5387d Table: adfc806a DAC: 00000051 Process cat (pid: 1730, stack limit = 0xee930210) Stack: (0xee931dd0 to 0xee932000) 1dc0: ee931dfc ee931de0 c058ae88 c058f1a4 1de0: edce3bc0 c07bfca4 edce3ac0 00001000 ee931e24 ee931e00 c01fcb90 c058ae48 1e00: 00000001 edce3bc0 00000000 00000001 ee931e50 ee8ff480 ee931e34 ee931e28 1e20: c01fb33c c01fcb0c ee931e8c ee931e38 c01a5210 c01fb314 ee931e9c ee931e48 1e40: 00000000 edce3bf0 befe4a00 ee931f78 00000000 00000000 000001e4 00000000 1e60: c00545a8 edce3ac0 00001000 00001000 befe4a00 ee931f78 00000000 00001000 1e80: ee931ed4 ee931e90 c01fbed8 c01a5038 ed085a58 00020000 00000000 00000000 1ea0: c0ad72e4 ee931f78 ee8ff488 ee8ff480 c077f3fc 00001000 befe4a00 ee931f78 1ec0: 00000000 00001000 ee931f44 ee931ed8 c017c328 c01fbdc4 00001000 00000000 1ee0: ee8ff480 00001000 ee931f44 ee931ef8 c017c65c c03deb10 ee931fac ee931f08 1f00: c0009270 c001f290 c0a8d968 ef2cb000 ef2cb000 ee8ff480 00000020 ee8ff480 1f20: ee8ff480 befe4a00 00001000 ee931f78 00000000 00000000 ee931f74 ee931f48 1f40: c017d1ec c017c2f8 c019c724 c019c684 ee8ff480 ee8ff480 00001000 befe4a00 1f60: 00000000 00000000 ee931fa4 ee931f78 c017d2a8 c017d160 00000000 00000000 1f80: 000a9f20 00001000 befe4a00 00000003 c000ffe4 ee930000 00000000 ee931fa8 1fa0: c000fe40 c017d264 000a9f20 00001000 00000003 befe4a00 00001000 00000000 Unable to handle kernel NULL pointer dereference at virtual address 0000000c 1fc0: 000a9f20 00001000 befe4a00 00000003 00000000 00000000 00000003 00000001 pgd = edfc4000 [0000000c] *pgd=bfcac835 1fe0: 00000000 befe49dc 000197f8 b6e35dfc 60070010 00000003 3065b49d 134ac2c9 [<c058f1bc>] (show_ignore_nice_load_gov_pol) from [<c058ae88>] (show+0x4c/0x60) [<c058ae88>] (show) from [<c01fcb90>] (sysfs_kf_seq_show+0x90/0xfc) [<c01fcb90>] (sysfs_kf_seq_show) from [<c01fb33c>] (kernfs_seq_show+0x34/0x38) [<c01fb33c>] (kernfs_seq_show) from [<c01a5210>] (seq_read+0x1e4/0x4e4) [<c01a5210>] (seq_read) from [<c01fbed8>] (kernfs_fop_read+0x120/0x1a0) [<c01fbed8>] (kernfs_fop_read) from [<c017c328>] (__vfs_read+0x3c/0xe0) [<c017c328>] (__vfs_read) from [<c017d1ec>] (vfs_read+0x98/0x104) [<c017d1ec>] (vfs_read) from [<c017d2a8>] (SyS_read+0x50/0x90) [<c017d2a8>] (SyS_read) from [<c000fe40>] (ret_fast_syscall+0x0/0x1c) Code: e5903044 e1a00001 e3081df4 e34c1092 (e593300c) ---[ end trace 5994b9a5111f35ee ]--- Fix that by making sure, policy->governor_data is updated at the right places only. Cc: 4.2+ <stable@vger.kernel.org> # 4.2+ Reported-and-tested-by: Juri Lelli <juri.lelli@arm.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2016-01-25 17:03:46 +00:00
policy->governor_data = NULL;
if (!have_governor_per_policy())
cdata->gdbs_data = NULL;
cdata->exit(dbs_data, !policy->governor->initialized);
free_common_dbs_info:
free_common_dbs_info(policy, cdata);
free_dbs_data:
kfree(dbs_data);
return ret;
}
static int cpufreq_governor_exit(struct cpufreq_policy *policy,
struct dbs_data *dbs_data)
{
struct common_dbs_data *cdata = dbs_data->cdata;
struct cpu_dbs_info *cdbs = cdata->get_cpu_cdbs(policy->cpu);
/* State should be equivalent to INIT */
if (!cdbs->shared || cdbs->shared->policy)
return -EBUSY;
if (!--dbs_data->usage_count) {
sysfs_remove_group(get_governor_parent_kobj(policy),
get_sysfs_attr(dbs_data));
cpufreq: Fix NULL reference crash while accessing policy->governor_data There is a race discovered by Juri, where we are able to: - create and read a sysfs file before policy->governor_data is being set to a non NULL value. OR - set policy->governor_data to NULL, and reading a file before being destroyed. And so such a crash is reported: Unable to handle kernel NULL pointer dereference at virtual address 0000000c pgd = edfc8000 [0000000c] *pgd=bfc8c835 Internal error: Oops: 17 [#1] SMP ARM Modules linked in: CPU: 4 PID: 1730 Comm: cat Not tainted 4.5.0-rc1+ #463 Hardware name: ARM-Versatile Express task: ee8e8480 ti: ee930000 task.ti: ee930000 PC is at show_ignore_nice_load_gov_pol+0x24/0x34 LR is at show+0x4c/0x60 pc : [<c058f1bc>] lr : [<c058ae88>] psr: a0070013 sp : ee931dd0 ip : ee931de0 fp : ee931ddc r10: ee4bc290 r9 : 00001000 r8 : ef2cb000 r7 : ee4bc200 r6 : ef2cb000 r5 : c0af57b0 r4 : ee4bc2e0 r3 : 00000000 r2 : 00000000 r1 : c0928df4 r0 : ef2cb000 Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5387d Table: adfc806a DAC: 00000051 Process cat (pid: 1730, stack limit = 0xee930210) Stack: (0xee931dd0 to 0xee932000) 1dc0: ee931dfc ee931de0 c058ae88 c058f1a4 1de0: edce3bc0 c07bfca4 edce3ac0 00001000 ee931e24 ee931e00 c01fcb90 c058ae48 1e00: 00000001 edce3bc0 00000000 00000001 ee931e50 ee8ff480 ee931e34 ee931e28 1e20: c01fb33c c01fcb0c ee931e8c ee931e38 c01a5210 c01fb314 ee931e9c ee931e48 1e40: 00000000 edce3bf0 befe4a00 ee931f78 00000000 00000000 000001e4 00000000 1e60: c00545a8 edce3ac0 00001000 00001000 befe4a00 ee931f78 00000000 00001000 1e80: ee931ed4 ee931e90 c01fbed8 c01a5038 ed085a58 00020000 00000000 00000000 1ea0: c0ad72e4 ee931f78 ee8ff488 ee8ff480 c077f3fc 00001000 befe4a00 ee931f78 1ec0: 00000000 00001000 ee931f44 ee931ed8 c017c328 c01fbdc4 00001000 00000000 1ee0: ee8ff480 00001000 ee931f44 ee931ef8 c017c65c c03deb10 ee931fac ee931f08 1f00: c0009270 c001f290 c0a8d968 ef2cb000 ef2cb000 ee8ff480 00000020 ee8ff480 1f20: ee8ff480 befe4a00 00001000 ee931f78 00000000 00000000 ee931f74 ee931f48 1f40: c017d1ec c017c2f8 c019c724 c019c684 ee8ff480 ee8ff480 00001000 befe4a00 1f60: 00000000 00000000 ee931fa4 ee931f78 c017d2a8 c017d160 00000000 00000000 1f80: 000a9f20 00001000 befe4a00 00000003 c000ffe4 ee930000 00000000 ee931fa8 1fa0: c000fe40 c017d264 000a9f20 00001000 00000003 befe4a00 00001000 00000000 Unable to handle kernel NULL pointer dereference at virtual address 0000000c 1fc0: 000a9f20 00001000 befe4a00 00000003 00000000 00000000 00000003 00000001 pgd = edfc4000 [0000000c] *pgd=bfcac835 1fe0: 00000000 befe49dc 000197f8 b6e35dfc 60070010 00000003 3065b49d 134ac2c9 [<c058f1bc>] (show_ignore_nice_load_gov_pol) from [<c058ae88>] (show+0x4c/0x60) [<c058ae88>] (show) from [<c01fcb90>] (sysfs_kf_seq_show+0x90/0xfc) [<c01fcb90>] (sysfs_kf_seq_show) from [<c01fb33c>] (kernfs_seq_show+0x34/0x38) [<c01fb33c>] (kernfs_seq_show) from [<c01a5210>] (seq_read+0x1e4/0x4e4) [<c01a5210>] (seq_read) from [<c01fbed8>] (kernfs_fop_read+0x120/0x1a0) [<c01fbed8>] (kernfs_fop_read) from [<c017c328>] (__vfs_read+0x3c/0xe0) [<c017c328>] (__vfs_read) from [<c017d1ec>] (vfs_read+0x98/0x104) [<c017d1ec>] (vfs_read) from [<c017d2a8>] (SyS_read+0x50/0x90) [<c017d2a8>] (SyS_read) from [<c000fe40>] (ret_fast_syscall+0x0/0x1c) Code: e5903044 e1a00001 e3081df4 e34c1092 (e593300c) ---[ end trace 5994b9a5111f35ee ]--- Fix that by making sure, policy->governor_data is updated at the right places only. Cc: 4.2+ <stable@vger.kernel.org> # 4.2+ Reported-and-tested-by: Juri Lelli <juri.lelli@arm.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2016-01-25 17:03:46 +00:00
policy->governor_data = NULL;
if (!have_governor_per_policy())
cdata->gdbs_data = NULL;
cdata->exit(dbs_data, policy->governor->initialized == 1);
kfree(dbs_data);
cpufreq: Fix NULL reference crash while accessing policy->governor_data There is a race discovered by Juri, where we are able to: - create and read a sysfs file before policy->governor_data is being set to a non NULL value. OR - set policy->governor_data to NULL, and reading a file before being destroyed. And so such a crash is reported: Unable to handle kernel NULL pointer dereference at virtual address 0000000c pgd = edfc8000 [0000000c] *pgd=bfc8c835 Internal error: Oops: 17 [#1] SMP ARM Modules linked in: CPU: 4 PID: 1730 Comm: cat Not tainted 4.5.0-rc1+ #463 Hardware name: ARM-Versatile Express task: ee8e8480 ti: ee930000 task.ti: ee930000 PC is at show_ignore_nice_load_gov_pol+0x24/0x34 LR is at show+0x4c/0x60 pc : [<c058f1bc>] lr : [<c058ae88>] psr: a0070013 sp : ee931dd0 ip : ee931de0 fp : ee931ddc r10: ee4bc290 r9 : 00001000 r8 : ef2cb000 r7 : ee4bc200 r6 : ef2cb000 r5 : c0af57b0 r4 : ee4bc2e0 r3 : 00000000 r2 : 00000000 r1 : c0928df4 r0 : ef2cb000 Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5387d Table: adfc806a DAC: 00000051 Process cat (pid: 1730, stack limit = 0xee930210) Stack: (0xee931dd0 to 0xee932000) 1dc0: ee931dfc ee931de0 c058ae88 c058f1a4 1de0: edce3bc0 c07bfca4 edce3ac0 00001000 ee931e24 ee931e00 c01fcb90 c058ae48 1e00: 00000001 edce3bc0 00000000 00000001 ee931e50 ee8ff480 ee931e34 ee931e28 1e20: c01fb33c c01fcb0c ee931e8c ee931e38 c01a5210 c01fb314 ee931e9c ee931e48 1e40: 00000000 edce3bf0 befe4a00 ee931f78 00000000 00000000 000001e4 00000000 1e60: c00545a8 edce3ac0 00001000 00001000 befe4a00 ee931f78 00000000 00001000 1e80: ee931ed4 ee931e90 c01fbed8 c01a5038 ed085a58 00020000 00000000 00000000 1ea0: c0ad72e4 ee931f78 ee8ff488 ee8ff480 c077f3fc 00001000 befe4a00 ee931f78 1ec0: 00000000 00001000 ee931f44 ee931ed8 c017c328 c01fbdc4 00001000 00000000 1ee0: ee8ff480 00001000 ee931f44 ee931ef8 c017c65c c03deb10 ee931fac ee931f08 1f00: c0009270 c001f290 c0a8d968 ef2cb000 ef2cb000 ee8ff480 00000020 ee8ff480 1f20: ee8ff480 befe4a00 00001000 ee931f78 00000000 00000000 ee931f74 ee931f48 1f40: c017d1ec c017c2f8 c019c724 c019c684 ee8ff480 ee8ff480 00001000 befe4a00 1f60: 00000000 00000000 ee931fa4 ee931f78 c017d2a8 c017d160 00000000 00000000 1f80: 000a9f20 00001000 befe4a00 00000003 c000ffe4 ee930000 00000000 ee931fa8 1fa0: c000fe40 c017d264 000a9f20 00001000 00000003 befe4a00 00001000 00000000 Unable to handle kernel NULL pointer dereference at virtual address 0000000c 1fc0: 000a9f20 00001000 befe4a00 00000003 00000000 00000000 00000003 00000001 pgd = edfc4000 [0000000c] *pgd=bfcac835 1fe0: 00000000 befe49dc 000197f8 b6e35dfc 60070010 00000003 3065b49d 134ac2c9 [<c058f1bc>] (show_ignore_nice_load_gov_pol) from [<c058ae88>] (show+0x4c/0x60) [<c058ae88>] (show) from [<c01fcb90>] (sysfs_kf_seq_show+0x90/0xfc) [<c01fcb90>] (sysfs_kf_seq_show) from [<c01fb33c>] (kernfs_seq_show+0x34/0x38) [<c01fb33c>] (kernfs_seq_show) from [<c01a5210>] (seq_read+0x1e4/0x4e4) [<c01a5210>] (seq_read) from [<c01fbed8>] (kernfs_fop_read+0x120/0x1a0) [<c01fbed8>] (kernfs_fop_read) from [<c017c328>] (__vfs_read+0x3c/0xe0) [<c017c328>] (__vfs_read) from [<c017d1ec>] (vfs_read+0x98/0x104) [<c017d1ec>] (vfs_read) from [<c017d2a8>] (SyS_read+0x50/0x90) [<c017d2a8>] (SyS_read) from [<c000fe40>] (ret_fast_syscall+0x0/0x1c) Code: e5903044 e1a00001 e3081df4 e34c1092 (e593300c) ---[ end trace 5994b9a5111f35ee ]--- Fix that by making sure, policy->governor_data is updated at the right places only. Cc: 4.2+ <stable@vger.kernel.org> # 4.2+ Reported-and-tested-by: Juri Lelli <juri.lelli@arm.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2016-01-25 17:03:46 +00:00
} else {
policy->governor_data = NULL;
}
free_common_dbs_info(policy, cdata);
return 0;
}
static int cpufreq_governor_start(struct cpufreq_policy *policy,
struct dbs_data *dbs_data)
{
struct common_dbs_data *cdata = dbs_data->cdata;
unsigned int sampling_rate, ignore_nice, j, cpu = policy->cpu;
struct cpu_dbs_info *cdbs = cdata->get_cpu_cdbs(cpu);
struct cpu_common_dbs_info *shared = cdbs->shared;
int io_busy = 0;
if (!policy->cur)
return -EINVAL;
/* State should be equivalent to INIT */
if (!shared || shared->policy)
return -EBUSY;
if (cdata->governor == GOV_CONSERVATIVE) {
struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
sampling_rate = cs_tuners->sampling_rate;
ignore_nice = cs_tuners->ignore_nice_load;
} else {
struct od_dbs_tuners *od_tuners = dbs_data->tuners;
sampling_rate = od_tuners->sampling_rate;
ignore_nice = od_tuners->ignore_nice_load;
io_busy = od_tuners->io_is_busy;
}
for_each_cpu(j, policy->cpus) {
struct cpu_dbs_info *j_cdbs = cdata->get_cpu_cdbs(j);
unsigned int prev_load;
j_cdbs->prev_cpu_idle =
get_cpu_idle_time(j, &j_cdbs->prev_cpu_wall, io_busy);
prev_load = (unsigned int)(j_cdbs->prev_cpu_wall -
j_cdbs->prev_cpu_idle);
j_cdbs->prev_load = 100 * prev_load /
(unsigned int)j_cdbs->prev_cpu_wall;
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
if (ignore_nice)
j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
cpufreq: governor: Be friendly towards latency-sensitive bursty workloads Cpufreq governors like the ondemand governor calculate the load on the CPU periodically by employing deferrable timers. A deferrable timer won't fire if the CPU is completely idle (and there are no other timers to be run), in order to avoid unnecessary wakeups and thus save CPU power. However, the load calculation logic is agnostic to all this, and this can lead to the problem described below. Time (ms) CPU 1 100 Task-A running 110 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 110.5 Task-A running 120 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. 125 Task-A went to sleep. With nothing else to do, CPU 1 went completely idle. 200 Task-A woke up and started running again. 200.5 Governor's deferred timer (which was originally programmed to fire at time 130) fires now. It calculates load for the time period 120 to 200.5, and finds the load is almost zero. Hence it decreases the CPU frequency to the minimum. 210 Governor's timer fires, finds load as 100% in the last 10ms interval and increases the CPU frequency. So, after the workload woke up and started running, the frequency was suddenly dropped to absolute minimum, and after that, there was an unnecessary delay of 10ms (sampling period) to increase the CPU frequency back to a reasonable value. And this pattern repeats for every wake-up-from-cpu-idle for that workload. This can be quite undesirable for latency- or response-time sensitive bursty workloads. So we need to fix the governor's logic to detect such wake-up-from- cpu-idle scenarios and start the workload at a reasonably high CPU frequency. One extreme solution would be to fake a load of 100% in such scenarios. But that might lead to undesirable side-effects such as frequency spikes (which might also need voltage changes) especially if the previous frequency happened to be very low. We just want to avoid the stupidity of dropping down the frequency to a minimum and then enduring a needless (and long) delay before ramping it up back again. So, let us simply carry forward the previous load - that is, let us just pretend that the 'load' for the current time-window is the same as the load for the previous window. That way, the frequency and voltage will continue to be set to whatever values they were set at previously. This means that bursty workloads will get a chance to influence the CPU frequency at which they wake up from cpu-idle, based on their past execution history. Thus, they might be able to avoid suffering from slow wakeups and long response-times. However, we should take care not to over-do this. For example, such a "copy previous load" logic will benefit cases like this: (where # represents busy and . represents idle) ##########.........#########.........###########...........##########........ but it will be detrimental in cases like the one shown below, because it will retain the high frequency (copied from the previous interval) even in a mostly idle system: ##########.........#.................#.....................#............... (i.e., the workload finished and the remaining tasks are such that their busy periods are smaller than the sampling interval, which causes the timer to always get deferred. So, this will make the copy-previous-load logic copy the initial high load to subsequent idle periods over and over again, thus keeping the frequency high unnecessarily). So, we modify this copy-previous-load logic such that it is used only once upon every wakeup-from-idle. Thus if we have 2 consecutive idle periods, the previous load won't get blindly copied over; cpufreq will freshly evaluate the load in the second idle interval, thus ensuring that the system comes back to its normal state. [ The right way to solve this whole problem is to teach the CPU frequency governors to also track load on a per-task basis, not just a per-CPU basis, and then use both the data sources intelligently to set the appropriate frequency on the CPUs. But that involves redesigning the cpufreq subsystem, so this patch should make the situation bearable until then. ] Experimental results: +-------------------+ I ran a modified version of ebizzy (called 'sleeping-ebizzy') that sleeps in between its execution such that its total utilization can be a user-defined value, say 10% or 20% (higher the utilization specified, lesser the amount of sleeps injected). This ebizzy was run with a single-thread, tied to CPU 8. Behavior observed with tracing (sample taken from 40% utilization runs): ------------------------------------------------------------------------ Without patch: ~~~~~~~~~~~~~~ kworker/8:2-12137 416.335742: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.335744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.345741: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.345744: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.345746: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.355738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> <...>-40753 416.402202: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 416.502130: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40753 416.505738: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.505739: cpu_frequency: state=2061000 cpu_id=8 kworker/8:2-12137 416.505741: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40753 416.515739: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-12137 416.515742: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-12137 416.515744: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy Observation: Ebizzy went idle at 416.402202, and started running again at 416.502130. But cpufreq noticed the long idle period, and dropped the frequency at 416.505739, only to increase it back again at 416.515742, realizing that the workload is in-fact CPU bound. Thus ebizzy needlessly ran at the lowest frequency for almost 13 milliseconds (almost 1 full sample period), and this pattern repeats on every sleep-wakeup. This could hurt latency-sensitive workloads quite a lot. With patch: ~~~~~~~~~~~ kworker/8:2-29802 464.832535: cpu_frequency: state=2061000 cpu_id=8 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 464.962538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.972533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 464.972536: cpu_frequency: state=4123000 cpu_id=8 kworker/8:2-29802 464.972538: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 464.982531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 <snip> --------------------------------------------------------------------- <snip> kworker/8:2-29802 465.022533: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.032531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.032532: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.035797: sched_switch: prev_comm=ebizzy ==> next_comm=swapper/8 <idle>-0 465.240178: sched_switch: prev_comm=swapper/8 ==> next_comm=ebizzy <...>-40738 465.242533: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 kworker/8:2-29802 465.242535: sched_switch: prev_comm=kworker/8:2 ==> next_comm=ebizzy <...>-40738 465.252531: sched_switch: prev_comm=ebizzy ==> next_comm=kworker/8:2 Observation: Ebizzy went idle at 465.035797, and started running again at 465.240178. Since ebizzy was the only real workload running on this CPU, cpufreq retained the frequency at 4.1Ghz throughout the run of ebizzy, no matter how many times ebizzy slept and woke-up in-between. Thus, ebizzy got the 10ms worth of 4.1 Ghz benefit during every sleep-wakeup (as compared to the run without the patch) and this boost gave a modest improvement in total throughput, as shown below. Sleeping-ebizzy records-per-second: ----------------------------------- Utilization Without patch With patch Difference (Absolute and % values) 10% 274767 277046 + 2279 (+0.829%) 20% 543429 553484 + 10055 (+1.850%) 40% 1090744 1107959 + 17215 (+1.578%) 60% 1634908 1662018 + 27110 (+1.658%) A rudimentary and somewhat approximately latency-sensitive workload such as sleeping-ebizzy itself showed a consistent, noticeable performance improvement with this patch. Hence, workloads that are truly latency-sensitive will benefit quite a bit from this change. Moreover, this is an overall win-win since this patch does not hurt power-savings at all (because, this patch does not reduce the idle time or idle residency; and the high frequency of the CPU when it goes to cpu-idle does not affect/hurt the power-savings of deep idle states). Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-06-07 20:41:43 +00:00
j_cdbs->update_util.func = dbs_update_util_handler;
}
shared->policy = policy;
if (cdata->governor == GOV_CONSERVATIVE) {
struct cs_cpu_dbs_info_s *cs_dbs_info =
cdata->get_cpu_dbs_info_s(cpu);
cs_dbs_info->down_skip = 0;
cs_dbs_info->requested_freq = policy->cur;
} else {
struct od_ops *od_ops = cdata->gov_ops;
struct od_cpu_dbs_info_s *od_dbs_info = cdata->get_cpu_dbs_info_s(cpu);
od_dbs_info->rate_mult = 1;
od_dbs_info->sample_type = OD_NORMAL_SAMPLE;
od_ops->powersave_bias_init_cpu(cpu);
}
gov_set_update_util(shared, sampling_rate);
return 0;
}
static int cpufreq_governor_stop(struct cpufreq_policy *policy,
struct dbs_data *dbs_data)
{
struct cpu_dbs_info *cdbs = dbs_data->cdata->get_cpu_cdbs(policy->cpu);
struct cpu_common_dbs_info *shared = cdbs->shared;
/* State should be equivalent to START */
if (!shared || !shared->policy)
return -EBUSY;
cpufreq: governor: replace per-CPU delayed work with timers cpufreq governors evaluate load at sampling rate and based on that they update frequency for a group of CPUs belonging to the same cpufreq policy. This is required to be done in a single thread for all policy->cpus, but because we don't want to wakeup idle CPUs to do just that, we use deferrable work for this. If we would have used a single delayed deferrable work for the entire policy, there were chances that the CPU required to run the handler can be in idle and we might end up not changing the frequency for the entire group with load variations. And so we were forced to keep per-cpu works, and only the one that expires first need to do the real work and others are rescheduled for next sampling time. We have been using the more complex solution until now, where we used a delayed deferrable work for this, which is a combination of a timer and a work. This could be made lightweight by keeping per-cpu deferred timers with a single work item, which is scheduled by the first timer that expires. This patch does just that and here are important changes: - The timer handler will run in irq context and so we need to use a spin_lock instead of the timer_mutex. And so a separate timer_lock is created. This also makes the use of the mutex and lock quite clear, as we know what exactly they are protecting. - A new field 'skip_work' is added to track when the timer handlers can queue a work. More comments present in code. Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-12-09 02:04:42 +00:00
gov_cancel_work(shared);
shared->policy = NULL;
return 0;
}
static int cpufreq_governor_limits(struct cpufreq_policy *policy,
struct dbs_data *dbs_data)
{
struct common_dbs_data *cdata = dbs_data->cdata;
unsigned int cpu = policy->cpu;
struct cpu_dbs_info *cdbs = cdata->get_cpu_cdbs(cpu);
/* State should be equivalent to START */
if (!cdbs->shared || !cdbs->shared->policy)
return -EBUSY;
mutex_lock(&cdbs->shared->timer_mutex);
if (policy->max < cdbs->shared->policy->cur)
__cpufreq_driver_target(cdbs->shared->policy, policy->max,
CPUFREQ_RELATION_H);
else if (policy->min > cdbs->shared->policy->cur)
__cpufreq_driver_target(cdbs->shared->policy, policy->min,
CPUFREQ_RELATION_L);
dbs_check_cpu(dbs_data, cpu);
mutex_unlock(&cdbs->shared->timer_mutex);
return 0;
}
int cpufreq_governor_dbs(struct cpufreq_policy *policy,
struct common_dbs_data *cdata, unsigned int event)
{
struct dbs_data *dbs_data;
int ret;
cpufreq: governor: Serialize governor callbacks There are several races reported in cpufreq core around governors (only ondemand and conservative) by different people. There are at least two race scenarios present in governor code: (a) Concurrent access/updates of governor internal structures. It is possible that fields such as 'dbs_data->usage_count', etc. are accessed simultaneously for different policies using same governor structure (i.e. CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag unset). And because of this we can dereference bad pointers. For example consider a system with two CPUs with separate 'struct cpufreq_policy' instances. CPU0 governor: ondemand and CPU1: powersave. CPU0 switching to powersave and CPU1 to ondemand: CPU0 CPU1 store* store* cpufreq_governor_exit() cpufreq_governor_init() dbs_data = cdata->gdbs_data; if (!--dbs_data->usage_count) kfree(dbs_data); dbs_data->usage_count++; *Bad pointer dereference* There are other races possible between EXIT and START/STOP/LIMIT as well. Its really complicated. (b) Switching governor state in bad sequence: For example trying to switch a governor to START state, when the governor is in EXIT state. There are some checks present in __cpufreq_governor() but they aren't sufficient as they compare events against 'policy->governor_enabled', where as we need to take governor's state into account, which can be used by multiple policies. These two issues need to be solved separately and the responsibility should be properly divided between cpufreq and governor core. The first problem is more about the governor core, as it needs to protect its structures properly. And the second problem should be fixed in cpufreq core instead of governor, as its all about sequence of events. This patch is trying to solve only the first problem. There are two types of data we need to protect, - 'struct common_dbs_data': No matter what, there is going to be a single copy of this per governor. - 'struct dbs_data': With CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag set, we will have per-policy copy of this data, otherwise a single copy. Because of such complexities, the mutex present in 'struct dbs_data' is insufficient to solve our problem. For example we need to protect fetching of 'dbs_data' from different structures at the beginning of cpufreq_governor_dbs(), to make sure it isn't currently being updated. This can be fixed if we can guarantee serialization of event parsing code for an individual governor. This is best solved with a mutex per governor, and the placeholder for that is 'struct common_dbs_data'. And so this patch moves the mutex from 'struct dbs_data' to 'struct common_dbs_data' and takes it at the beginning and drops it at the end of cpufreq_governor_dbs(). Tested with and without following configuration options: CONFIG_LOCKDEP_SUPPORT=y CONFIG_DEBUG_RT_MUTEXES=y CONFIG_DEBUG_PI_LIST=y CONFIG_DEBUG_SPINLOCK=y CONFIG_DEBUG_MUTEXES=y CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y CONFIG_LOCKDEP=y CONFIG_DEBUG_ATOMIC_SLEEP=y Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-06-03 10:27:13 +00:00
/* Lock governor to block concurrent initialization of governor */
mutex_lock(&cdata->mutex);
if (have_governor_per_policy())
dbs_data = policy->governor_data;
else
dbs_data = cdata->gdbs_data;
if (!dbs_data && (event != CPUFREQ_GOV_POLICY_INIT)) {
cpufreq: governor: Serialize governor callbacks There are several races reported in cpufreq core around governors (only ondemand and conservative) by different people. There are at least two race scenarios present in governor code: (a) Concurrent access/updates of governor internal structures. It is possible that fields such as 'dbs_data->usage_count', etc. are accessed simultaneously for different policies using same governor structure (i.e. CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag unset). And because of this we can dereference bad pointers. For example consider a system with two CPUs with separate 'struct cpufreq_policy' instances. CPU0 governor: ondemand and CPU1: powersave. CPU0 switching to powersave and CPU1 to ondemand: CPU0 CPU1 store* store* cpufreq_governor_exit() cpufreq_governor_init() dbs_data = cdata->gdbs_data; if (!--dbs_data->usage_count) kfree(dbs_data); dbs_data->usage_count++; *Bad pointer dereference* There are other races possible between EXIT and START/STOP/LIMIT as well. Its really complicated. (b) Switching governor state in bad sequence: For example trying to switch a governor to START state, when the governor is in EXIT state. There are some checks present in __cpufreq_governor() but they aren't sufficient as they compare events against 'policy->governor_enabled', where as we need to take governor's state into account, which can be used by multiple policies. These two issues need to be solved separately and the responsibility should be properly divided between cpufreq and governor core. The first problem is more about the governor core, as it needs to protect its structures properly. And the second problem should be fixed in cpufreq core instead of governor, as its all about sequence of events. This patch is trying to solve only the first problem. There are two types of data we need to protect, - 'struct common_dbs_data': No matter what, there is going to be a single copy of this per governor. - 'struct dbs_data': With CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag set, we will have per-policy copy of this data, otherwise a single copy. Because of such complexities, the mutex present in 'struct dbs_data' is insufficient to solve our problem. For example we need to protect fetching of 'dbs_data' from different structures at the beginning of cpufreq_governor_dbs(), to make sure it isn't currently being updated. This can be fixed if we can guarantee serialization of event parsing code for an individual governor. This is best solved with a mutex per governor, and the placeholder for that is 'struct common_dbs_data'. And so this patch moves the mutex from 'struct dbs_data' to 'struct common_dbs_data' and takes it at the beginning and drops it at the end of cpufreq_governor_dbs(). Tested with and without following configuration options: CONFIG_LOCKDEP_SUPPORT=y CONFIG_DEBUG_RT_MUTEXES=y CONFIG_DEBUG_PI_LIST=y CONFIG_DEBUG_SPINLOCK=y CONFIG_DEBUG_MUTEXES=y CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y CONFIG_LOCKDEP=y CONFIG_DEBUG_ATOMIC_SLEEP=y Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-06-03 10:27:13 +00:00
ret = -EINVAL;
goto unlock;
}
switch (event) {
case CPUFREQ_GOV_POLICY_INIT:
ret = cpufreq_governor_init(policy, dbs_data, cdata);
break;
case CPUFREQ_GOV_POLICY_EXIT:
ret = cpufreq_governor_exit(policy, dbs_data);
break;
case CPUFREQ_GOV_START:
ret = cpufreq_governor_start(policy, dbs_data);
break;
case CPUFREQ_GOV_STOP:
ret = cpufreq_governor_stop(policy, dbs_data);
break;
case CPUFREQ_GOV_LIMITS:
ret = cpufreq_governor_limits(policy, dbs_data);
break;
default:
ret = -EINVAL;
}
cpufreq: governor: Serialize governor callbacks There are several races reported in cpufreq core around governors (only ondemand and conservative) by different people. There are at least two race scenarios present in governor code: (a) Concurrent access/updates of governor internal structures. It is possible that fields such as 'dbs_data->usage_count', etc. are accessed simultaneously for different policies using same governor structure (i.e. CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag unset). And because of this we can dereference bad pointers. For example consider a system with two CPUs with separate 'struct cpufreq_policy' instances. CPU0 governor: ondemand and CPU1: powersave. CPU0 switching to powersave and CPU1 to ondemand: CPU0 CPU1 store* store* cpufreq_governor_exit() cpufreq_governor_init() dbs_data = cdata->gdbs_data; if (!--dbs_data->usage_count) kfree(dbs_data); dbs_data->usage_count++; *Bad pointer dereference* There are other races possible between EXIT and START/STOP/LIMIT as well. Its really complicated. (b) Switching governor state in bad sequence: For example trying to switch a governor to START state, when the governor is in EXIT state. There are some checks present in __cpufreq_governor() but they aren't sufficient as they compare events against 'policy->governor_enabled', where as we need to take governor's state into account, which can be used by multiple policies. These two issues need to be solved separately and the responsibility should be properly divided between cpufreq and governor core. The first problem is more about the governor core, as it needs to protect its structures properly. And the second problem should be fixed in cpufreq core instead of governor, as its all about sequence of events. This patch is trying to solve only the first problem. There are two types of data we need to protect, - 'struct common_dbs_data': No matter what, there is going to be a single copy of this per governor. - 'struct dbs_data': With CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag set, we will have per-policy copy of this data, otherwise a single copy. Because of such complexities, the mutex present in 'struct dbs_data' is insufficient to solve our problem. For example we need to protect fetching of 'dbs_data' from different structures at the beginning of cpufreq_governor_dbs(), to make sure it isn't currently being updated. This can be fixed if we can guarantee serialization of event parsing code for an individual governor. This is best solved with a mutex per governor, and the placeholder for that is 'struct common_dbs_data'. And so this patch moves the mutex from 'struct dbs_data' to 'struct common_dbs_data' and takes it at the beginning and drops it at the end of cpufreq_governor_dbs(). Tested with and without following configuration options: CONFIG_LOCKDEP_SUPPORT=y CONFIG_DEBUG_RT_MUTEXES=y CONFIG_DEBUG_PI_LIST=y CONFIG_DEBUG_SPINLOCK=y CONFIG_DEBUG_MUTEXES=y CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y CONFIG_LOCKDEP=y CONFIG_DEBUG_ATOMIC_SLEEP=y Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2015-06-03 10:27:13 +00:00
unlock:
mutex_unlock(&cdata->mutex);
return ret;
}
EXPORT_SYMBOL_GPL(cpufreq_governor_dbs);