linux/kernel/time
Lingutla Chandrasekhar c52232a49e timers: Forward timer base before migrating timers
On CPU hotunplug the enqueued timers of the unplugged CPU are migrated to a
live CPU. This happens from the control thread which initiated the unplug.

If the CPU on which the control thread runs came out from a longer idle
period then the base clock of that CPU might be stale because the control
thread runs prior to any event which forwards the clock.

In such a case the timers from the unplugged CPU are queued on the live CPU
based on the stale clock which can cause large delays due to increased
granularity of the outer timer wheels which are far away from base:;clock.

But there is a worse problem than that. The following sequence of events
illustrates it:

 - CPU0 timer1 is queued expires = 59969 and base->clk = 59131.

   The timer is queued at wheel level 2, with resulting expiry time = 60032
   (due to level granularity).

 - CPU1 enters idle @60007, with next timer expiry @60020.

 - CPU0 is hotplugged at @60009

 - CPU1 exits idle and runs the control thread which migrates the
   timers from CPU0

   timer1 is now queued in level 0 for immediate handling in the next
   softirq because the requested expiry time 59969 is before CPU1 base->clk
   60007

 - CPU1 runs code which forwards the base clock which succeeds because the
   next expiring timer. which was collected at idle entry time is still set
   to 60020.

   So it forwards beyond 60007 and therefore misses to expire the migrated
   timer1. That timer gets expired when the wheel wraps around again, which
   takes between 63 and 630ms depending on the HZ setting.

Address both problems by invoking forward_timer_base() for the control CPUs
timer base. All other places, which might run into a similar problem
(mod_timer()/add_timer_on()) already invoke forward_timer_base() to avoid
that.

[ tglx: Massaged comment and changelog ]

Fixes: a683f390b9 ("timers: Forward the wheel clock whenever possible")
Co-developed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: linux-arm-msm@vger.kernel.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180118115022.6368-1-clingutla@codeaurora.org
2018-02-28 23:34:33 +01:00
..
alarmtimer.c alarmtimer: Ensure RTC module is not unloaded 2017-08-31 21:36:45 +02:00
clockevents.c clockevents: Retry programming min delta up to 10 times 2017-10-19 16:29:15 +02:00
clocksource.c treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
hrtimer.c hrtimer: remove unneeded kallsyms include 2018-02-06 18:32:47 -08:00
itimer.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
jiffies.c jiffies: Revert bogus conversion of NSEC_PER_SEC to TICK_NSEC 2017-03-07 11:03:28 +01:00
Kconfig sched/isolation: Make CONFIG_NO_HZ_FULL select CONFIG_CPU_ISOLATION 2017-12-18 13:46:42 +01:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ntp_internal.h Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 17:56:58 -08:00
ntp.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 17:56:58 -08:00
posix-clock.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
posix-cpu-timers.c Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-01-30 11:55:56 -08:00
posix-stubs.c posix-stubs: Use get_timespec64() and put_timespec64() 2017-10-17 17:22:27 +02:00
posix-timers.c signal: Replace memset(info,...) with clear_siginfo for clarity 2018-01-22 19:07:08 -06:00
posix-timers.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sched_clock.c timers, sched_clock: Update timeout for clock wrap 2017-03-23 12:30:27 -07:00
test_udelay.c time: Avoid timespec in udelay_test 2016-06-20 12:47:26 -07:00
tick-broadcast-hrtimer.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
tick-broadcast.c tick/broadcast: Make tick_broadcast_setup_oneshot() static 2017-06-12 18:56:01 +02:00
tick-common.c ktime: Cleanup ktime_set() usage 2016-12-25 17:21:22 +01:00
tick-internal.h hrtimer: Unify remote enqueue handling 2018-01-16 02:53:58 +01:00
tick-oneshot.c clockevents: Update clockevents device next_event on stop 2017-11-01 18:20:17 +01:00
tick-sched.c hrtimer: Optimize the hrtimer code by using static keys for migration_enable/nohz_active 2018-01-16 02:35:44 +01:00
tick-sched.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
time.c Merge branch 'fortglx/4.15/time' of https://git.linaro.org/people/john.stultz/linux into timers/core 2017-10-31 23:17:28 +01:00
timeconst.bc time: Introduce jiffies64_to_nsecs() 2017-02-01 09:13:45 +01:00
timeconv.c time: Add time64_to_tm() 2016-06-20 12:47:15 -07:00
timecounter.c clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
timekeeping_debug.c PM / timekeeping: Print debug messages when requested 2017-07-23 00:03:43 +02:00
timekeeping_internal.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
timekeeping.c timekeeping: Remove CONFIG_GENERIC_TIME_VSYSCALL_OLD 2017-11-14 11:20:25 +01:00
timekeeping.h Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 17:56:58 -08:00
timer_list.c timer/debug: Change /proc/timer_list from 0444 to 0400 2017-11-13 16:04:06 +01:00
timer.c timers: Forward timer base before migrating timers 2018-02-28 23:34:33 +01:00