linux-kernel - Re: [PATCH] perf stat: improve readability of shadow stats

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Date:   Tue, 2 Mar 2021 11:08:40 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Changbin Du <changbin.du@...il.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] perf stat: improve readability of shadow stats

On Tue, Mar 2, 2021 at 4:19 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Tue, Mar 02, 2021 at 01:24:02AM +0800, Changbin Du wrote:
> > This does follow two changes:
> >   1) Select appropriate unit between K/M/G.
> >   2) Use 'cpu-sec' instead of 'sec' to state this is not the wall-time.
> >
> > $ sudo ./perf stat -a -- sleep 1
> >
> > Before: Unit 'M' is selected even the number is very small.
> >  Performance counter stats for 'system wide':
> >
> >           4,003.06 msec cpu-clock                 #    3.998 CPUs utilized
> >             16,179      context-switches          #    0.004 M/sec
> >                161      cpu-migrations            #    0.040 K/sec
> >              4,699      page-faults               #    0.001 M/sec
> >      6,135,801,925      cycles                    #    1.533 GHz                      (83.21%)
> >      5,783,308,491      stalled-cycles-frontend   #   94.26% frontend cycles idle     (83.21%)
> >      4,543,694,050      stalled-cycles-backend    #   74.05% backend cycles idle      (66.49%)
> >      4,720,130,587      instructions              #    0.77  insn per cycle
> >                                                   #    1.23  stalled cycles per insn  (83.28%)
> >        753,848,078      branches                  #  188.318 M/sec                    (83.61%)
> >         37,457,747      branch-misses             #    4.97% of all branches          (83.48%)
> >
> >        1.001283725 seconds time elapsed
> >
> > After:
> > $ sudo ./perf stat -a -- sleep 2
> >
> >  Performance counter stats for 'system wide':
> >
> >           8,003.20 msec cpu-clock                 #    3.998 CPUs utilized
> >              9,768      context-switches          #    1.221 K/cpu-sec
> >                164      cpu-migrations            #   20.492  /cpu-sec
>
> should you remove also the leading '/' in ' /cpu-sec' ?

The change looks good.  And I think we should keep '/' otherwise it'd be
more confusing.

>
>
> SNIP
>
> > @@ -1270,18 +1271,14 @@ void perf_stat__print_shadow_stats(struct perf_stat_config *config,
> >               generic_metric(config, evsel->metric_expr, evsel->metric_events, NULL,
> >                               evsel->name, evsel->metric_name, NULL, 1, cpu, out, st);
> >       } else if (runtime_stat_n(st, STAT_NSECS, cpu, &rsd) != 0) {
> > -             char unit = 'M';
> > +             char unit = ' ';
> >               char unit_buf[10];
> >
> >               total = runtime_stat_avg(st, STAT_NSECS, cpu, &rsd);
> > -
> >               if (total)
> > -                     ratio = 1000.0 * avg / total;
> > -             if (ratio < 0.001) {
> > -                     ratio *= 1000;
> > -                     unit = 'K';
> > -             }
> > -             snprintf(unit_buf, sizeof(unit_buf), "%c/sec", unit);
> > +                     ratio = convert_unit_double(1000000000.0 * avg / total, &unit);
> > +
> > +             snprintf(unit_buf, sizeof(unit_buf), "%c/cpu-sec", unit);
> >               print_metric(config, ctxp, NULL, "%8.3f", unit_buf, ratio);
>
> hum this will change -x output that people parse, so I don't think we can do that

Agreed.

>
> >       } else if (perf_stat_evsel__is(evsel, SMI_NUM)) {
> >               print_smi_cost(config, cpu, out, st, &rsd);
> > diff --git a/tools/perf/util/units.c b/tools/perf/util/units.c
> > index a46762aec4c9..ac13b5ecde31 100644
> > --- a/tools/perf/util/units.c
> > +++ b/tools/perf/util/units.c
> > @@ -55,6 +55,28 @@ unsigned long convert_unit(unsigned long value, char *unit)
> >       return value;
> >  }
> >
> > +double convert_unit_double(double value, char *unit)
> > +{
> > +     *unit = ' ';
> > +
> > +     if (value > 1000.0) {
> > +             value /= 1000.0;
> > +             *unit = 'K';
> > +     }
> > +
> > +     if (value > 1000.0) {
> > +             value /= 1000.0;
> > +             *unit = 'M';
> > +     }
> > +
> > +     if (value > 1000.0) {
> > +             value /= 1000.0;
> > +             *unit = 'G';
> > +     }
> > +
> > +     return value;
> > +}
>
> we have convert_unit function just above doing the same only with
> unsigned long.. let's have one base function with double values and
> another one casting the result to unsigned long

Sounds good.

Thanks,
Namhyung