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>
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@ -96,6 +96,10 @@ armpmu_event_set_period(struct perf_event *event,
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s64 period = hwc->sample_period;
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s64 period = hwc->sample_period;
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int ret = 0;
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int ret = 0;
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/* The period may have been changed by PERF_EVENT_IOC_PERIOD */
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if (unlikely(period != hwc->last_period))
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left = period - (hwc->last_period - left);
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if (unlikely(left <= -period)) {
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if (unlikely(left <= -period)) {
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left = period;
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left = period;
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local64_set(&hwc->period_left, left);
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local64_set(&hwc->period_left, left);
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