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sched: Ensure cpu_power periodic update

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With a lot of small tasks, the softirq sched is nearly never called
when no_hz is enabled. In this case load_balance() is mainly called
with the newly_idle mode which doesn't update the cpu_power.

Add a next_update field which ensure a maximum update period when
there is short activity.

Having stale cpu_power information can skew the load-balancing
decisions, this is cured by the guaranteed update.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1323717668-2143-1-git-send-email-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot 2011-12-12 20:21:08 +01:00 committed by Ingo Molnar
parent 39be350127
commit 4ec4412e1e
2 changed files with 17 additions and 8 deletions
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1
include/linux/sched.h
View File

@ -905,6 +905,7 @@ struct sched_group_power {
* single CPU.
*/
unsigned int power, power_orig;
unsigned long next_update;
/*
* Number of busy cpus in this group.
*/

24
kernel/sched/fair.c
View File

@ -215,6 +215,8 @@ calc_delta_mine(unsigned long delta_exec, unsigned long weight,
const struct sched_class fair_sched_class;
static unsigned long __read_mostly max_load_balance_interval = HZ/10;
/**************************************************************
* CFS operations on generic schedulable entities:
*/
@ -3776,6 +3778,11 @@ void update_group_power(struct sched_domain *sd, int cpu)
struct sched_domain *child = sd->child;
struct sched_group *group, *sdg = sd->groups;
unsigned long power;
unsigned long interval;
interval = msecs_to_jiffies(sd->balance_interval);
interval = clamp(interval, 1UL, max_load_balance_interval);
sdg->sgp->next_update = jiffies + interval;
if (!child) {
update_cpu_power(sd, cpu);
@ -3883,12 +3890,15 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
* domains. In the newly idle case, we will allow all the cpu's
* to do the newly idle load balance.
*/
if (idle != CPU_NEWLY_IDLE && local_group) {
if (balance_cpu != this_cpu) {
*balance = 0;
return;
}
update_group_power(sd, this_cpu);
if (local_group) {
if (idle != CPU_NEWLY_IDLE) {
if (balance_cpu != this_cpu) {
*balance = 0;
return;
}
update_group_power(sd, this_cpu);
} else if (time_after_eq(jiffies, group->sgp->next_update))
update_group_power(sd, this_cpu);
}
/* Adjust by relative CPU power of the group */
@ -4945,8 +4955,6 @@ static int __cpuinit sched_ilb_notifier(struct notifier_block *nfb,
static DEFINE_SPINLOCK(balancing);
static unsigned long __read_mostly max_load_balance_interval = HZ/10;
/*
* Scale the max load_balance interval with the number of CPUs in the system.
* This trades load-balance latency on larger machines for less cross talk.