Re: [PATCH 2/3] perf metricgroup: Fix uncore metric expressions

[Ian Rogers]

On Wed, Sep 9, 2020 at 2:53 AM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> Hi Ian,
>
> On Wed, Sep 9, 2020 at 5:02 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> >
> > A metric like DRAM_BW_Use has on SkylakeX events uncore_imc/cas_count_read/
> > and uncore_imc/case_count_write/. These events open 6 events per socket
> > with pmu names of uncore_imc_[0-5]. The current metric setup code in
> > find_evsel_group assumes one ID will map to 1 event to be recorded in
> > metric_events. For events with multiple matches, the first event is
> > recorded in metric_events (avoiding matching >1 event with the same
> > name) and the evlist_used updated so that duplicate events aren't
> > removed when the evlist has unused events removed.
> >
> > Before this change:
> > $ /tmp/perf/perf stat -M DRAM_BW_Use -a -- sleep 1
> >
> >  Performance counter stats for 'system wide':
> >
> >              41.14 MiB  uncore_imc/cas_count_read/
> >      1,002,614,251 ns   duration_time
> >
> >        1.002614251 seconds time elapsed
> >
> > After this change:
> > $ /tmp/perf/perf stat -M DRAM_BW_Use -a -- sleep 1
> >
> >  Performance counter stats for 'system wide':
> >
> >             157.47 MiB  uncore_imc/cas_count_read/ #     0.00 DRAM_BW_Use
>
> Hmm.. I guess the 0.00 result is incorrect, no?

Agreed. There are a number of pre-existing bugs in this code. I'll try
to look into this one.

> >             126.97 MiB  uncore_imc/cas_count_write/
> >      1,003,019,728 ns   duration_time
> >
> > Erroneous duplication introduced in:
> > commit 2440689d62e9 ("perf metricgroup: Remove duped metric group events").
> >
> > Fixes: ded80bda8bc9 ("perf expr: Migrate expr ids table to a hashmap").
> > Reported-by: Jin, Yao <yao.jin@xxxxxxxxxxxxxxx>
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> [SNIP]
> > @@ -248,6 +260,16 @@ static struct evsel *find_evsel_group(struct evlist *perf_evlist,
> >                 ev = metric_events[i];
> >                 ev->metric_leader = ev;
> >                 set_bit(ev->idx, evlist_used);
> > +               /*
> > +                * Mark two events with identical names in the same group as
> > +                * being in use as uncore events may be duplicated for each pmu.
> > +                */
> > +               evlist__for_each_entry(perf_evlist, ev) {
> > +                       if (metric_events[i]->leader == ev->leader &&
> > +                           !strcmp(metric_events[i]->name, ev->name)) {
> > +                               set_bit(ev->idx, evlist_used);
>
> I'm not sure whether they are grouped together.
> But if so, you can use for_each_group_member(ev, leader).

Good suggestion, unfortunately the groups may be removed for things
like NMI watchdog or --metric-no-group and so there wouldn't be a
leader to follow. We could do something like this:

if (metric_events[i]->leader) {
  for_each_group_member(ev, leader) {
    if (!strcmp(metric_events[i]->name, ev->name))
      set_bit(ev->idx, evlist_used);
  }
} else {
  evlist__for_each_entry(perf_evlist, ev) {
    if (!ev->leader && !strcmp(metric_events[i]->name, ev->name))
      set_bit(ev->idx, evlist_used);
  }
 }
}

What do you think?

Thanks,
Ian

> Thanks
> Namhyung
>
>
> > +                       }
> > +               }
> >         }
> >
> >         return metric_events[0];
> > --
> > 2.28.0.526.ge36021eeef-goog
> >