linux/kernel/time
Frederic Weisbecker f99973e18b nohz: Fix buggy tick delay on IRQ storms
When the tick is stopped and we reach the dynticks evaluation code on
IRQ exit, we perform a soft tick restart if we observe an expired timer
from there. It means we program the nearest possible tick but we stay in
dynticks mode (ts->tick_stopped = 1) because we may need to stop the tick
again after that expired timer is handled.

Now this solution works most of the time but if we suffer an IRQ storm
and those interrupts trigger faster than the hardware clockevents min
delay, our tick won't fire until that IRQ storm is finished.

Here is the problem: on IRQ exit we reprog the timer to at least
NOW() + min_clockevents_delay. Another IRQ fires before the tick so we
reschedule again to NOW() + min_clockevents_delay, etc... The tick
is eternally rescheduled min_clockevents_delay ahead.

A solution is to simply remove this soft tick restart. After all
the normal dynticks evaluation path can handle 0 delay just fine. And
by doing that we benefit from the optimization branch which avoids
clock reprogramming if the clockevents deadline hasn't changed since
the last reprog. This fixes our issue because we don't do repetitive
clock reprog that always add hardware min delay.

As a side effect it should even optimize the 0 delay path in general.

Reported-and-tested-by: Octavian Purdila <octavian.purdila@nxp.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1496328429-13317-1-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-05 09:33:50 +02:00
..
alarmtimer.c time: Change k_clock nsleep() to use timespec64 2017-04-14 21:49:56 +02:00
clockevents.c clockevents: Make clockevents_config() static 2017-03-23 12:14:05 -07:00
clocksource.c sched/clock, clocksource: Add optional cs::mark_unstable() method 2017-01-14 11:29:43 +01:00
hrtimer.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2017-05-02 19:09:35 -07:00
itimer.c sched/headers: Prepare to move cputime functionality from <linux/sched.h> into <linux/sched/cputime.h> 2017-03-02 08:42:39 +01:00
jiffies.c jiffies: Revert bogus conversion of NSEC_PER_SEC to TICK_NSEC 2017-03-07 11:03:28 +01:00
Kconfig rcu: Drop RCU_USER_QS in favor of NO_HZ_FULL 2015-07-06 13:52:18 -07:00
Makefile time: Remove CONFIG_TIMER_STATS 2017-02-10 11:15:08 +01:00
ntp_internal.h ntp: Fix second_overflow's input parameter type to be 64bits 2015-12-16 16:50:56 -08:00
ntp.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
posix-clock.c time: Change k_clock timer_set() and timer_get() to use timespec64 2017-04-14 21:49:56 +02:00
posix-cpu-timers.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2017-05-05 11:08:43 -07:00
posix-stubs.c time: Change k_clock nsleep() to use timespec64 2017-04-14 21:49:56 +02:00
posix-timers.c time: Change k_clock nsleep() to use timespec64 2017-04-14 21:49:56 +02:00
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 ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
tick-broadcast.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-02-20 10:06:32 -08:00
tick-common.c ktime: Cleanup ktime_set() usage 2016-12-25 17:21:22 +01:00
tick-internal.h timers: Forward the wheel clock whenever possible 2016-07-07 10:35:11 +02:00
tick-oneshot.c ktime: Get rid of the union 2016-12-25 17:21:22 +01:00
tick-sched.c nohz: Fix buggy tick delay on IRQ storms 2017-06-05 09:33:50 +02:00
tick-sched.h nohz: Fix collision between tick and other hrtimers, again 2017-05-17 08:19:47 +02:00
time.c time: delete current_fs_time() 2017-05-12 15:57:15 -07:00
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 timekeeping: Use deferred printk() in debug code 2017-02-15 11:46:08 +01:00
timekeeping_internal.h clocksource: Use a plain u64 instead of cycle_t 2016-12-25 11:04:12 +01:00
timekeeping.c timekeeping: Remove pointless conversion to bool 2017-03-31 10:26:56 +02:00
timekeeping.h timekeeping: Remove unused timekeeping_{get,set}_tai_offset() 2017-01-06 16:47:28 -08:00
timer_list.c sysrq: Reset the watchdog timers while displaying high-resolution timers 2017-03-23 12:46:53 -07:00
timer.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2017-05-02 19:09:35 -07:00