Commit d7842da4 authored Oct 20, 2010 by Stephane Eranian Committed by Ingo Molnar Oct 22, 2010

perf_events: Fix for transaction recovery in group_sched_in()



This new version (see commit 8e5fc1a7) is much simpler and ensures that
in case of error in group_sched_in() during event_sched_in(), the
events up to the failed event go through regular event_sched_out().
But the failed event and the remaining events in the group have their
timings adjusted as if they had also gone through event_sched_in() and
event_sched_out(). This ensures timing uniformity across all events in
a group. This also takes care of the tstamp_stopped problem in case
the group could never be scheduled. The tstamp_stopped is updated as
if the event had actually run.

With this patch, the following now reports correct time_enabled,
in case the NMI watchdog is active:

$ task -e unhalted_core_cycles,instructions_retired,baclears,baclears
noploop 1
noploop for 1 seconds

0 unhalted_core_cycles (100.00% scaling, ena=997,552,872, run=0)
0 instructions_retired (100.00% scaling, ena=997,552,872, run=0)
0 baclears (100.00% scaling, ena=997,552,872, run=0)
0 baclears (100.00% scaling, ena=997,552,872, run=0)

And the older test case also works:

$ task -einstructions_retired,baclears,baclears -e
unhalted_core_cycles,baclears,baclears sleep 5

1680885 instructions_retired (69.39% scaling, ena=950756, run=291006)
  10735 baclears (69.39% scaling, ena=950756, run=291006)
  10735 baclears (69.39% scaling, ena=950756, run=291006)

      0 unhalted_core_cycles (100.00% scaling, ena=817932, run=0)
      0 baclears (100.00% scaling, ena=817932, run=0)
      0 baclears (100.00% scaling, ena=817932, run=0)

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4cbeeebc.8ee7d80a.5a28.0d5f@mx.google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 9ffcfa6f

kernel/perf_event.c

+20 −2

Original line number	Diff line number	Diff line
		@@ -691,6 +691,8 @@ group_sched_in(struct perf_event *group_event,
		{
		struct perf_event event, partial_group = NULL;
		struct pmu *pmu = group_event->pmu;
		u64 now = ctx->time;
		bool simulate = false;

		if (group_event->state == PERF_EVENT_STATE_OFF)
		return 0;
		@@ -719,12 +721,28 @@ group_sched_in(struct perf_event *group_event,
		/*
		* Groups can be scheduled in as one unit only, so undo any
		* partial group before returning:
		* The events up to the failed event are scheduled out normally,
		* tstamp_stopped will be updated.
		*
		* The failed events and the remaining siblings need to have
		* their timings updated as if they had gone thru event_sched_in()
		* and event_sched_out(). This is required to get consistent timings
		* across the group. This also takes care of the case where the group
		* could never be scheduled by ensuring tstamp_stopped is set to mark
		* the time the event was actually stopped, such that time delta
		* calculation in update_event_times() is correct.
		*/
		list_for_each_entry(event, &group_event->sibling_list, group_entry) {
		if (event == partial_group)
		break;
		simulate = true;

		if (simulate) {
		event->tstamp_running += now - event->tstamp_stopped;
		event->tstamp_stopped = now;
		} else {
		event_sched_out(event, cpuctx, ctx);
		}
		}
		event_sched_out(group_event, cpuctx, ctx);

		pmu->cancel_txn(pmu);