time/sched_clock: Expire timer in hardirq context (2c8bd588) · Commits · 戴 / test

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

kernel/time/sched_clock.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -208,7 +208,8 @@ 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;
		@@ -254,9 +255,9 @@ 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);
		}

		/*
		@@ -293,7 +294,7 @@ 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;
		}

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