On Wed, 2010-03-10 at 22:17 -0800, eran...@google.com wrote: > This patch fixes a bug in 2.6.33 X86 event scheduling whereby > all counts are bogus as soon as events need to be multiplexed > because the PMU is overcommitted. > > The code in hw_perf_enable() was causing multiplexed events > to accumulate collected counts twice causing bogus results. > > This is demonstrated on AMD Barcelona with the example > below. First run, no conflict, you obtain the actual counts. > Second run, PMU overcommitted, multiplexing, all events are > over-counted. Third run, patch applied, you obtain the correct > count through scaling. >
I'm a bit puzzled by this one, if we, during scheduling move an event from idx 1 to idx 2, we need to stop it on 1 and start if on 2, otherwise we do not properly transfer its count, right? With the below patch it does no such thing. I did fix some funnies I observed with hw_perf_enable() while doing the PEBS stuff, and -tip does it wrong differently from what you illustrate, so while there defenately is something to fix, I doubt the below is correct. > Signed-off-by: Stephane Eranian <eran...@google.com> > -- > perf_event.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/arch/x86/kernel/cpu/perf_event.c > b/arch/x86/kernel/cpu/perf_event.c > index 97cddbf..ef5d63f 100644 > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -818,8 +818,6 @@ void hw_perf_enable(void) > match_prev_assignment(hwc, cpuc, i)) > continue; > > - x86_pmu_stop(event); > - > hwc->idx = -1; > } ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
