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time/sched_clock: Expire timer in hardirq context 

[ Upstream commit 2c8bd58812ee3dbf0d78b566822f7eacd34bdd7b ]

To minimize latency, PREEMPT_RT kernels expires hrtimers in preemptible
softirq context by default. This can be overriden by marking the timer's
expiry with HRTIMER_MODE_HARD.

sched_clock_timer is missing this annotation: if its callback is preempted
and the duration of the preemption exceeds the wrap around time of the
underlying clocksource, sched clock will get out of sync.

Mark the sched_clock_timer for expiry in hard interrupt context.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200309181529.26558-1-a.darwish@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Ahmed S. Darwish 2020-03-09 18:15:29 +00:00 committed by Greg Kroah-Hartman
parent 3f755f5233
commit 2902207377
1 changed files with 5 additions and 4 deletions
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9
kernel/time/sched_clock.c
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@ -207,7 +207,8 @@ sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
if (sched_clock_timer.function != NULL) {
/* update timeout for clock wrap */
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
hrtimer_start(&sched_clock_timer, cd.wrap_kt,
HRTIMER_MODE_REL_HARD);
}
r = rate;
@ -251,9 +252,9 @@ void __init generic_sched_clock_init(void)
* Start the timer to keep sched_clock() properly updated and
* sets the initial epoch.
*/
hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
sched_clock_timer.function = sched_clock_poll;
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD);
}
/*
@ -290,7 +291,7 @@ void sched_clock_resume(void)
struct clock_read_data *rd = &cd.read_data[0];
rd->epoch_cyc = cd.actual_read_sched_clock();
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD);
rd->read_sched_clock = cd.actual_read_sched_clock;
}