Messages in this thread | | | From | Namhyung Kim <> | Date | Tue, 11 Oct 2022 11:20:54 -0700 | Subject | Re: [PATCH V2 2/6] perf/x86/intel/pebs: Fix PEBS timestamps overwritten |
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Hello,
On Thu, Sep 1, 2022 at 6:10 AM <kan.liang@linux.intel.com> wrote: > > From: Kan Liang <kan.liang@linux.intel.com> > > The PEBS TSC-based timestamps do not appear correctly in the final > perf.data output file from perf record. > > The data->time field setup by PEBS in the setup_pebs_fixed_sample_data() > is later overwritten by perf_events generic code in > perf_prepare_sample(). There is an ordering problem. > > Set the sample flags when the data->time is updated by PEBS. > The data->time field will not be overwritten anymore.
I have a report that it breaks the symbolization of samples. It seems time is not in sync between perf_clock and PEBS.
One thing I noticed is that the system has a config option CONFIG_HAVE_UNSTABLE_SCHED_CLOCK=y. Looking at the code, it seems sched_clock is doing some adjustments in that case. So I'm not sure if it'd work well on those systems.
Thoughts?
Thanks, Namhyung
> > Reported-by: Andreas Kogler <andreas.kogler.0x@gmail.com> > Reported-by: Stephane Eranian <eranian@google.com> > Signed-off-by: Kan Liang <kan.liang@linux.intel.com> > --- > arch/x86/events/intel/ds.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c > index de1f55d51784..01cbe26225c2 100644 > --- a/arch/x86/events/intel/ds.c > +++ b/arch/x86/events/intel/ds.c > @@ -1643,8 +1643,10 @@ static void setup_pebs_fixed_sample_data(struct perf_event *event, > * We can only do this for the default trace clock. > */ > if (x86_pmu.intel_cap.pebs_format >= 3 && > - event->attr.use_clockid == 0) > + event->attr.use_clockid == 0) { > data->time = native_sched_clock_from_tsc(pebs->tsc); > + data->sample_flags |= PERF_SAMPLE_TIME; > + } > > if (has_branch_stack(event)) > data->br_stack = &cpuc->lbr_stack; > @@ -1705,8 +1707,10 @@ static void setup_pebs_adaptive_sample_data(struct perf_event *event, > perf_sample_data_init(data, 0, event->hw.last_period); > data->period = event->hw.last_period; > > - if (event->attr.use_clockid == 0) > + if (event->attr.use_clockid == 0) { > data->time = native_sched_clock_from_tsc(basic->tsc); > + data->sample_flags |= PERF_SAMPLE_TIME; > + } > > /* > * We must however always use iregs for the unwinder to stay sane; the > -- > 2.35.1 >
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