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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>
This commit is contained in:
Will Deacon 2012-10-17 12:01:34 +01:00 committed by Russell King
parent 2456f44dd7
commit 3581fe0ef3
1 changed files with 4 additions and 0 deletions
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4
arch/arm/kernel/perf_event.c
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@ -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);