Messages in this thread Patch in this message | | | Date | Fri, 29 Jan 2010 09:30:56 GMT | From | tip-bot for Peter Zijlstra <> | Subject | [tip:perf/core] perf_events: Fix sample_period transfer on inherit |
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Commit-ID: 75c9f3284a7ff957829f44baace82406a6354ceb Gitweb: http://git.kernel.org/tip/75c9f3284a7ff957829f44baace82406a6354ceb Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Fri, 29 Jan 2010 09:04:26 +0100 Committer: Ingo Molnar <mingo@elte.hu> CommitDate: Fri, 29 Jan 2010 09:15:26 +0100
perf_events: Fix sample_period transfer on inherit
One problem with frequency driven counters is that we cannot predict the rate at which they trigger, therefore we have to start them at period=1, this causes a ramp up effect. However, if we fail to propagate the stable state on fork each new child will have to ramp up again. This can lead to significant artifacts in sample data.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: eranian@google.com Cc: Mike Galbraith <efault@gmx.de> Cc: Paul Mackerras <paulus@samba.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> LKML-Reference: <1264752266.4283.2121.camel@laptop> Signed-off-by: Ingo Molnar <mingo@elte.hu> --- kernel/perf_event.c | 11 +++++++++-- 1 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 251fb95..53dc2a3 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -5002,8 +5002,15 @@ inherit_event(struct perf_event *parent_event, else child_event->state = PERF_EVENT_STATE_OFF; - if (parent_event->attr.freq) - child_event->hw.sample_period = parent_event->hw.sample_period; + if (parent_event->attr.freq) { + u64 sample_period = parent_event->hw.sample_period; + struct hw_perf_event *hwc = &child_event->hw; + + hwc->sample_period = sample_period; + hwc->last_period = sample_period; + + atomic64_set(&hwc->period_left, sample_period); + } child_event->overflow_handler = parent_event->overflow_handler;
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