Commit 3581fe0e authored Oct 17, 2012 by Will Deacon Committed by Russell King Oct 18, 2012

ARM: 7556/1: perf: fix updated event period in response to PERF_EVENT_IOC_PERIOD



The PERF_EVENT_IOC_PERIOD ioctl command can be used to change the
sample period of a running perf_event. Consequently, when calculating
the next event period, the new period will only be considered after the
previous one has overflowed.

This patch changes the calculation of the remaining event ticks so that
they are offset if the period has changed.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reported-by: Andreas Sandberg <andreas.sandberg@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

parent 2456f44d

arch/arm/kernel/perf_event.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -96,6 +96,10 @@ armpmu_event_set_period(struct perf_event *event,
		s64 period = hwc->sample_period;
		int ret = 0;

		/* The period may have been changed by PERF_EVENT_IOC_PERIOD */
		if (unlikely(period != hwc->last_period))
		left = period - (hwc->last_period - left);

		if (unlikely(left <= -period)) {
		left = period;
		local64_set(&hwc->period_left, left);