Messages in this thread Patch in this message | | | Subject | [PATCH 9/8] perf_events: Restore sanity to scaling land | From | Peter Zijlstra <> | Date | Mon, 23 Nov 2009 15:00:36 +0100 |
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It is quite possible to call update_event_times() on a context that isn't actually running and thereby confuse the thing.
perf stat was reporting !100% scale values for software counters (2e2af50b perf_events: Disable events when we detach them, solved the worst of that, but there was still some left).
The thing that happens is that because we are not self-reaping (we have a caring parent) there is a time between the last schedule (out) and having do_exit() called which will detach the events.
This period would be accounted as enabled,!running because the event->state==INACTIVE, even though !event->ctx->is_active.
Similar issues could have been observed by calling read() on a event while the attached task was not scheduled in.
Solve this by teaching update_event_times() about ctx->is_active.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- kernel/perf_event.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 0b0d5f7..0aafe85 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -274,7 +274,12 @@ static void update_event_times(struct perf_event *event) event->group_leader->state < PERF_EVENT_STATE_INACTIVE) return; - event->total_time_enabled = ctx->time - event->tstamp_enabled; + if (ctx->is_active) + run_end = ctx->time; + else + run_end = event->tstamp_stopped; + + event->total_time_enabled = run_end - event->tstamp_enabled; if (event->state == PERF_EVENT_STATE_INACTIVE) run_end = event->tstamp_stopped;
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