From 3581fe0ef37ce12ac7a4f74831168352ae848edc Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 17 Oct 2012 12:01:34 +0100 Subject: [PATCH] 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 Reported-by: Andreas Sandberg Signed-off-by: Will Deacon Signed-off-by: Russell King --- arch/arm/kernel/perf_event.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c index 93971b1a4f0b..53c0304b734a 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); -- 2.20.1