Commit f9fccdb9 authored Apr 21, 2017 by Peter Zijlstra Committed by Ingo Molnar May 15, 2017

cpuidle: Fix idle time tracking



Ville reported that on his Core2, which has TSC stop in idle, we would
always report very short idle durations. He tracked this down to
commit:

  e93e59ce ("cpuidle: Replace ktime_get() with local_clock()")

which replaces ktime_get() with local_clock().

Add a sched_clock_idle_wakeup_event() call, which will re-sync the
clock with ktime_get_ns() when TSC is unstable and no-op otherwise.

Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Fixes: e93e59ce ("cpuidle: Replace ktime_get() with local_clock()")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 3067a33d

drivers/cpuidle/cpuidle.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -220,6 +220,7 @@ int cpuidle_enter_state(struct cpuidle_device dev, struct cpuidle_driver drv,
		entered_state = target_state->enter(dev, drv, index);
		start_critical_timings();

		sched_clock_idle_wakeup_event();
		time_end = ns_to_ktime(local_clock());
		trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);

kernel/sched/clock.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -410,14 +410,21 @@ void sched_clock_idle_sleep_event(void)
		EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);

		/*
		* We just idled; resync with ktime. (called with irqs disabled):
		* We just idled; resync with ktime.
		*/
		void sched_clock_idle_wakeup_event(void)
		{
		if (timekeeping_suspended)
		unsigned long flags;

		if (sched_clock_stable())
		return;

		if (unlikely(timekeeping_suspended))
		return;

		local_irq_save(flags);
		sched_clock_tick();
		local_irq_restore(flags);
		}
		EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

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