perf: Fix running time accounting

A recent fix to the shadow timestamp inadvertly broke the running time
accounting.

We must not update the running timestamp if we fail to schedule the
event, the event will not have ran. This can (and did) result in
negative total runtime because the stopped timestamp was before the
running timestamp (we 'started' but never stopped the event -- because
it never really started we didn't have to stop it either).

Reported-and-Tested-by: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 72f669c0086f ("perf: Update shadow timestamp before add event")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org # 4.1
Cc: Shaohua Li <shli@fb.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d3dae3419b99566c127f1682b29f39bb184bbdb1..10d076b2572c0d24cb4275328250118dd6c0bc9e 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1868,8 +1868,6 @@ event_sched_in(struct perf_event *event,
 
        perf_pmu_disable(event->pmu);
 
-       event->tstamp_running += tstamp - event->tstamp_stopped;
-
        perf_set_shadow_time(event, ctx, tstamp);
 
        perf_log_itrace_start(event);
@@ -1881,6 +1879,8 @@ event_sched_in(struct perf_event *event,
                goto out;
        }
 
+       event->tstamp_running += tstamp - event->tstamp_stopped;
+
        if (!is_software_event(event))
                cpuctx->active_oncpu++;
        if (!ctx->nr_active++)