path: root/arch
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authorWill Deacon <will.deacon@arm.com>2012-10-17 12:01:34 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2012-10-18 11:05:20 +0100
commit3581fe0ef37ce12ac7a4f74831168352ae848edc (patch)
tree50c5dc84d1d60879c6843ab7c49c165da8f5bffa /arch
parent2456f44dd7a9aaffc2cd21a13f78198b3d94da08 (diff)
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>
Diffstat (limited to 'arch')
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 93971b1a4f0..53c0304b734 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -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);