linux-kernel - Re: [PATCH v4 09/10] perf stat: Read tool events last

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Message-ID: <CAP-5=fVidOjNDZCX6Ain83KFp0Zk8aHTJX7_KgwfTY885DuPKg@mail.gmail.com>
Date: Mon, 17 Nov 2025 20:38:15 -0800
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	"Dr. David Alan Gilbert" <linux@...blig.org>, Yang Li <yang.lee@...ux.alibaba.com>, 
	James Clark <james.clark@...aro.org>, Thomas Falcon <thomas.falcon@...el.com>, 
	Thomas Richter <tmricht@...ux.ibm.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH v4 09/10] perf stat: Read tool events last

On Mon, Nov 17, 2025 at 6:35 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Thu, Nov 13, 2025 at 10:05:15AM -0800, Ian Rogers wrote:
> > When reading a metric like memory bandwidth on multiple sockets, the
> > additional sockets will be on CPUS > 0. Because of the affinity
> > reading, the counters are read on CPU 0 along with the time, then the
> > later sockets are read. This can lead to the later sockets having a
> > bandwidth larger than is possible for the period of time. To avoid
> > this moving the reading of tool events to occur after all other events
> > are read.
>
> Can you move this change before the affinity updates?  I think it's
> straight-forward and can be applied independently.

It is straightforward but will require changes to
read_counters_with_affinity. I can do a v5 once I know what to do with
the other patches.

Thanks,
Ian

> Thanks,
> Namhyung
>
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >  tools/perf/builtin-stat.c | 29 ++++++++++++++++++++++++++++-
> >  tools/perf/util/evlist.c  |  4 ----
> >  2 files changed, 28 insertions(+), 5 deletions(-)
> >
> > diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> > index 947f11b8b106..aec93b91fd11 100644
> > --- a/tools/perf/builtin-stat.c
> > +++ b/tools/perf/builtin-stat.c
> > @@ -379,6 +379,9 @@ static int read_counters_with_affinity(void)
> >               if (evsel__is_bpf(counter))
> >                       continue;
> >
> > +             if (evsel__is_tool(counter))
> > +                     continue;
> > +
> >               if (!counter->err)
> >                       counter->err = read_counter_cpu(counter, evlist_cpu_itr.cpu_map_idx);
> >       }
> > @@ -402,6 +405,24 @@ static int read_bpf_map_counters(void)
> >       return 0;
> >  }
> >
> > +static int read_tool_counters(void)
> > +{
> > +     struct evsel *counter;
> > +
> > +     evlist__for_each_entry(evsel_list, counter) {
> > +             int idx;
> > +
> > +             if (!evsel__is_tool(counter))
> > +                     continue;
> > +
> > +             perf_cpu_map__for_each_idx(idx, counter->core.cpus) {
> > +                     if (!counter->err)
> > +                             counter->err = read_counter_cpu(counter, idx);
> > +             }
> > +     }
> > +     return 0;
> > +}
> > +
> >  static int read_counters(void)
> >  {
> >       int ret;
> > @@ -415,7 +436,13 @@ static int read_counters(void)
> >               return ret;
> >
> >       // Read non-BPF and non-tool counters next.
> > -     return read_counters_with_affinity();
> > +     ret = read_counters_with_affinity();
> > +     if (ret)
> > +             return ret;
> > +
> > +     // Read the tool counters last. This way the duration_time counter
> > +     // should always be greater than any other counter's enabled time.
> > +     return read_tool_counters();
> >  }
> >
> >  static void process_counters(void)
> > diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> > index b6df81b8a236..fc3dae7cdfca 100644
> > --- a/tools/perf/util/evlist.c
> > +++ b/tools/perf/util/evlist.c
> > @@ -368,10 +368,6 @@ static bool evlist__use_affinity(struct evlist *evlist)
> >       struct perf_cpu_map *used_cpus = NULL;
> >       bool ret = false;
> >
> > -     /*
> > -      * With perf record core.user_requested_cpus is usually NULL.
> > -      * Use the old method to handle this for now.
> > -      */
> >       if (!evlist->core.user_requested_cpus ||
> >           cpu_map__is_dummy(evlist->core.user_requested_cpus))
> >               return false;
> > --
> > 2.51.2.1041.gc1ab5b90ca-goog
> >