On Tue, 21 Jul 2015, Peter Zijlstra wrote:
> On Tue, Jul 21, 2015 at 02:14:54PM -0400, Vince Weaver wrote:
> > Hello
> >
> > I have a new AMD A8 system and perf multiplexing support is acting weird.
> >
> > If I run the perf_event_tests check_multiplexing test it fails like this:
> >
> > Event TotalCount RawCount Scale
> > ScaledCount Error
> > 0 500282143 150403975 -2.00 (c8050b5 fffffffff9c224ef)
> > -300807950 160.13%
> >
> > So the problem is that the TOTAL_TIME_RUNNING value is negative, which as
> > far as I know shouldn't be possible.
>
> Correct, that should not happen. I don't have a Fam16 machine, but I can
> try and stare at the code a wee bit. Although there's another few perf
> issues I am still looking into as well :/
well I've traced it back to see that in
update_event_times()
run_end is less than event->tstamp_running, which is why the result
is negative.
[ 1279.857205] VMW: 1 run_end=1279846999345 tstamp_running=1279929016607
[ 1279.857222] VMW: 0 run_end=1279855184453 tstamp_running=1279931111760
It seems to happen both in the PERF_EVENT_STATE_INACTIVE and
!PERF_EVENT_STATE_INACTIVE cases.
tracking back why those values are wrong is proving to be a bit trickier.
Vince
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