Commit bad7192b authored Nov 27, 2013 by Peter Zijlstra Committed by Ingo Molnar Dec 17, 2013

perf: Fix PERF_EVENT_IOC_PERIOD to force-reset the period



Vince Weaver reports that, on all architectures apart from ARM,
PERF_EVENT_IOC_PERIOD doesn't actually update the period until the next
event fires. This is counter-intuitive behaviour and is better dealt
with in the core code.

This patch ensures that the period is forcefully reset when dealing with
such a request in the core code. A subsequent patch removes the
equivalent hack from the ARM back-end.

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/1385560479-11014-1-git-send-email-will.deacon@arm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 7fd565e2

kernel/events/core.c

+15 −1

Original line number	Diff line number	Diff line
		@@ -3527,7 +3527,7 @@ static void perf_event_for_each(struct perf_event *event,
		static int perf_event_period(struct perf_event event, u64 __user arg)
		{
		struct perf_event_context *ctx = event->ctx;
		int ret = 0;
		int ret = 0, active;
		u64 value;

		if (!is_sampling_event(event))
		@@ -3551,6 +3551,20 @@ static int perf_event_period(struct perf_event event, u64 __user arg)
		event->attr.sample_period = value;
		event->hw.sample_period = value;
		}

		active = (event->state == PERF_EVENT_STATE_ACTIVE);
		if (active) {
		perf_pmu_disable(ctx->pmu);
		event->pmu->stop(event, PERF_EF_UPDATE);
		}

		local64_set(&event->hw.period_left, 0);

		if (active) {
		event->pmu->start(event, PERF_EF_RELOAD);
		perf_pmu_enable(ctx->pmu);
		}

		unlock:
		raw_spin_unlock_irq(&ctx->lock);