Re: [PATCH v4 03/18] perf jevents: Add set of common metrics based on default ones

[Namhyung Kim <namhyung@kernel.org>]

On Fri, Nov 14, 2025 at 08:57:39AM -0800, Ian Rogers wrote:
> On Fri, Nov 14, 2025 at 8:28 AM James Clark <james.clark@linaro.org> wrote:
> >
> >
> >
> > On 11/11/2025 9:21 pm, Ian Rogers wrote:
> > > Add support to getting a common set of metrics from a default
> > > table. It simplifies the generation to add json metrics at the same
> > > time. The metrics added are CPUs_utilized, cs_per_second,
> > > migrations_per_second, page_faults_per_second, insn_per_cycle,
> > > stalled_cycles_per_instruction, frontend_cycles_idle,
> > > backend_cycles_idle, cycles_frequency, branch_frequency and
> > > branch_miss_rate based on the shadow metric definitions.
> > >
> > > Following this change the default perf stat output on an alderlake
> > > looks like:
> > > ```
> > > $ perf stat -a -- sleep 2
> > >
> > >   Performance counter stats for 'system wide':
> > >
> > >                0.00 msec cpu-clock                        #    0.000 CPUs utilized
> > >              77,739      context-switches
> > >              15,033      cpu-migrations
> > >             321,313      page-faults
> > >      14,355,634,225      cpu_atom/instructions/           #    1.40  insn per cycle              (35.37%)
> > >     134,561,560,583      cpu_core/instructions/           #    3.44  insn per cycle              (57.85%)
> > >      10,263,836,145      cpu_atom/cycles/                                                        (35.42%)
> > >      39,138,632,894      cpu_core/cycles/                                                        (57.60%)
> > >       2,989,658,777      cpu_atom/branches/                                                      (42.60%)
> > >      32,170,570,388      cpu_core/branches/                                                      (57.39%)
> > >          29,789,870      cpu_atom/branch-misses/          #    1.00% of all branches             (42.69%)
> > >         165,991,152      cpu_core/branch-misses/          #    0.52% of all branches             (57.19%)
> > >                         (software)                 #      nan cs/sec  cs_per_second
> > >               TopdownL1 (cpu_core)                 #     11.9 %  tma_bad_speculation
> > >                                                    #     19.6 %  tma_frontend_bound       (63.97%)
> > >               TopdownL1 (cpu_core)                 #     18.8 %  tma_backend_bound
> > >                                                    #     49.7 %  tma_retiring             (63.97%)
> > >                         (software)                 #      nan faults/sec  page_faults_per_second
> > >                                                    #      nan GHz  cycles_frequency       (42.88%)
> > >                                                    #      nan GHz  cycles_frequency       (69.88%)
> > >               TopdownL1 (cpu_atom)                 #     11.7 %  tma_bad_speculation
> > >                                                    #     29.9 %  tma_retiring             (50.07%)
> > >               TopdownL1 (cpu_atom)                 #     31.3 %  tma_frontend_bound       (43.09%)
> > >                         (cpu_atom)                 #      nan M/sec  branch_frequency     (43.09%)
> > >                                                    #      nan M/sec  branch_frequency     (70.07%)
> > >                                                    #      nan migrations/sec  migrations_per_second
> > >               TopdownL1 (cpu_atom)                 #     27.1 %  tma_backend_bound        (43.08%)
> > >                         (software)                 #      0.0 CPUs  CPUs_utilized
> > >                                                    #      1.4 instructions  insn_per_cycle  (43.04%)
> > >                                                    #      3.5 instructions  insn_per_cycle  (69.99%)
> > >                                                    #      1.0 %  branch_miss_rate         (35.46%)
> > >                                                    #      0.5 %  branch_miss_rate         (65.02%)
> > >
> > >         2.005626564 seconds time elapsed
> > > ```
> > >
> > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > ---
> > >   .../arch/common/common/metrics.json           |  86 +++++++++++++
> > >   tools/perf/pmu-events/empty-pmu-events.c      | 115 +++++++++++++-----
> > >   tools/perf/pmu-events/jevents.py              |  21 +++-
> > >   tools/perf/pmu-events/pmu-events.h            |   1 +
> > >   tools/perf/util/metricgroup.c                 |  31 +++--
> > >   5 files changed, 212 insertions(+), 42 deletions(-)
> > >   create mode 100644 tools/perf/pmu-events/arch/common/common/metrics.json
> > >
> > > diff --git a/tools/perf/pmu-events/arch/common/common/metrics.json b/tools/perf/pmu-events/arch/common/common/metrics.json
> > > new file mode 100644
> > > index 000000000000..d915be51e300
> > > --- /dev/null
> > > +++ b/tools/perf/pmu-events/arch/common/common/metrics.json
> > > @@ -0,0 +1,86 @@
> > > +[
> > > +    {
> > > +        "BriefDescription": "Average CPU utilization",
> > > +        "MetricExpr": "(software@cpu\\-clock\\,name\\=cpu\\-clock@ if #target_cpu else software@task\\-clock\\,name\\=task\\-clock@) / (duration_time * 1e9)",
> >
> > Hi Ian,
> >
> > I noticed that this metric is making "perf stat tests" fail.
> > "duration_time" is a tool event and they don't work with "perf stat
> > record" anymore. The test tests the record command with the default args
> > which results in this event being used and a failure.
> >
> > I suppose there are three issues. First two are unrelated to this change:
> >
> >   - Perf stat record continues to write out a bad perf.data file even
> >     though it knows that tool events won't work.
> >
> >     For example 'status' ends up being -1 in cmd_stat() but it's ignored
> >     for some of the writing parts. It does decide to not print any stdout
> >     though:
> >
> >     $ perf stat record -e "duration_time"
> >     <blank>
> >
> >   - The other issue is obviously that tool events don't work with perf
> >     stat record which seems to be a regression from 6828d6929b76 ("perf
> >     evsel: Refactor tool events")
> >
> >   - The third issue is that this change adds a broken tool event to the
> >     default output of perf stat
> >
> > I'm not actually sure what "perf stat record" is for? It's possible that
> > it's not used anymore, expecially if nobody noticed that tool events
> > haven't been working in it for a while.
> >
> > I think we're also supposed to have json output for perf stat (although
> > this is also broken in some obscure scenarios), so maybe perf stat
> > record isn't needed anymore?
> 
> Hi James,
> 
> Thanks for the report. I think this is also an overlap with perf stat
> metrics don't work with perf stat record, and because these changes
> made that the default. Let me do some follow up work as the perf
> script work shows we can do useful things with metrics while not being
> on a live perf stat - there's the obstacle that the CPUID of the host
> will be used :-/
> 
> Anyway, I'll take a look and we should add a test on this. There is
> one that the perf stat json output is okay, to some definition. One
> problem is that the stat-display code is complete spaghetti. Now that
> stat-shadow only handles json metrics, and perf script isn't trying to
> maintain a set of shadow counters, that is a little bit improved.

I have another test failure on this.  On my AMD machine, perf all
metrics test fails due to missing "LLC-loads" events.

  $ sudo perf stat -M llc_miss_rate true
  Error:
  No supported events found.
  The LLC-loads event is not supported.

Maybe we need to make some cache metrics conditional as some events are
missing.

Thanks,
Namhyung