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perf/x86-ibs: Trigger overflow if remaining period is too small 

There are cases where the remaining period is smaller than the minimal
possible value. In this case the counter is restarted with the minimal
period. This is of no use as the interrupt handler will trigger
immediately again and most likely hits itself. This biases the
results.

So, if the remaining period is within the min range, we better do not
restart the counter and instead trigger the overflow.

Signed-off-by: Robert Richter <robert.richter@amd.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1333390758-10893-9-git-send-email-robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
hifive-unleashed-5.1
Robert Richter 2012-04-02 20:19:14 +02:00 committed by Ingo Molnar
parent 98112d2e95
commit fc006cf7cc
1 changed files with 1 additions and 4 deletions
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5
arch/x86/kernel/cpu/perf_event_amd_ibs.c
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@ -78,16 +78,13 @@ perf_event_set_period(struct hw_perf_event *hwc, u64 min, u64 max, u64 *hw_perio
overflow = 1;
}
if (unlikely(left <= 0)) {
if (unlikely(left < (s64)min)) {
left += period;
local64_set(&hwc->period_left, left);
hwc->last_period = period;
overflow = 1;
}
if (unlikely(left < min))
left = min;
if (left > max)
left = max;