On Fri, 2010-10-15 at 16:54 +0200, Stephane Eranian wrote: > The group_sched_in() function uses a transactional approach to schedule > a group of events. In a group, either all events can be scheduled or > none are. To schedule each event in, the function calls event_sched_in(). > In case of error, event_sched_out() is called on each event in the group. > > The problem is that event_sched_out() does not completely cancel the > effects of event_sched_in(). Furthermore event_sched_out() changes the > state of the event as if it had run which is not true is this particular > case. > > Those inconsistencies impact time tracking fields and may lead to events > in a group not all reporting the same time_enabled and time_running values. > This is demonstrated with the example below: > > $ task -eunhalted_core_cycles,baclears,baclears -e > unhalted_core_cycles,baclears,baclears sleep 5 > 1946101 unhalted_core_cycles (32.85% scaling, ena=829181, run=556827) > 11423 baclears (32.85% scaling, ena=829181, run=556827) > 7671 baclears (0.00% scaling, ena=556827, run=556827) > > 2250443 unhalted_core_cycles (57.83% scaling, ena=962822, run=405995) > 11705 baclears (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 <eran...@google.com>
Yes, makes sense.. I'm a bit hesitant to slap a -stable tag on it due to its size,.. Ingo, Paulus? ------------------------------------------------------------------------------ Download new Adobe(R) Flash(R) Builder(TM) 4 The new Adobe(R) Flex(R) 4 and Flash(R) Builder(TM) 4 (formerly Flex(R) Builder(TM)) enable the development of rich applications that run across multiple browsers and platforms. Download your free trials today! http://p.sf.net/sfu/adobe-dev2dev _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
