ears (57.83% scaling, ena=962822, run=405995) 11705 baclears (57.83% scaling, ena=962822, run=405995) Notice that in the first group, the last baclears event does not report the same timings as its siblings. This issue comes from the fact that tstamp_stopped is updated by event_sched_out() as if the event had actually run. To solve the issue, we must ensure that, in case of error, there is no change in the event state whatsoever. That means timings must remain as they were when entering group_sched_in(). To do this we defer updating tstamp_running until we know the transaction succeeded. Therefore, we have split event_sched_in() in two parts separating the update to tstamp_running. Similarly, in case of error, we do not want to update tstamp_stopped. Therefore, we have split event_sched_out() in two parts separating the update to tstamp_stopped. With this patch, we now get the following output: $ task -eunhalted_core_cycles,baclears,baclears -e unhalted_core_cycles,baclears,baclears sleep 5 2492050 unhalted_core_cycles (71.75% scaling, ena=1093330, run=308841) 11243 baclears (71.75% scaling, ena=1093330, run=308841) 11243 baclears (71.75% scaling, ena=1093330, run=308841) 1852746 unhalted_core_cycles (0.00% scaling, ena=784489, run=784489) 9253 baclears (0.00% scaling, ena=784489, run=784489) 9253 baclears (0.00% scaling, ena=784489, run=784489) Note that the uneven timing between groups is a side effect of the process spending most of its time sleeping, i.e., not enough event rotations (but that's a separate issue). Signed-off-by: Stephane Eranian Signed-off-by: Peter Zijlstra LKML-Reference: <4cb86b4c.41e9d80a.44e9.3e19@mx.google.com> Signed-off-by: Ingo Molnar Ԍ