Commit 75c9f328 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar

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: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent 18c01f8a
...@@ -5002,8 +5002,15 @@ inherit_event(struct perf_event *parent_event, ...@@ -5002,8 +5002,15 @@ inherit_event(struct perf_event *parent_event,
else else
child_event->state = PERF_EVENT_STATE_OFF; child_event->state = PERF_EVENT_STATE_OFF;
if (parent_event->attr.freq) if (parent_event->attr.freq) {
child_event->hw.sample_period = parent_event->hw.sample_period; 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; child_event->overflow_handler = parent_event->overflow_handler;
......
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