linux-kernel - Re: [PATCH 3/5] perf cpumap: Add intersect function.

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Message-ID: <CAP-5=fVfYtu=wcfUQEzwuJMhxexi3d8hVqF5QFLkj_FWPHLK5Q@mail.gmail.com>
Date:   Mon, 28 Mar 2022 13:54:06 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Kajol Jain <kjain@...ux.ibm.com>,
        James Clark <james.clark@....com>,
        German Gomez <german.gomez@....com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Riccardo Mancini <rickyman7@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>,
        Alexander Antonov <alexander.antonov@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 3/5] perf cpumap: Add intersect function.

On Mon, Mar 28, 2022 at 1:28 PM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Em Sun, Mar 27, 2022 at 11:24:12PM -0700, Ian Rogers escreveu:
> > The merge function gives the union of two cpu maps. Add an intersect
> > function which will be used in the next change.
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >  tools/lib/perf/cpumap.c              | 38 ++++++++++++++++++++++++++++
> >  tools/lib/perf/include/perf/cpumap.h |  2 ++
> >  2 files changed, 40 insertions(+)
> >
> > diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
> > index 953bc50b0e41..56b4d213039f 100644
> > --- a/tools/lib/perf/cpumap.c
> > +++ b/tools/lib/perf/cpumap.c
> > @@ -393,3 +393,41 @@ struct perf_cpu_map *perf_cpu_map__merge(struct perf_cpu_map *orig,
> >       perf_cpu_map__put(orig);
> >       return merged;
> >  }
> > +
> > +struct perf_cpu_map *perf_cpu_map__intersect(struct perf_cpu_map *orig,
> > +                                          struct perf_cpu_map *other)
> > +{
> > +     struct perf_cpu *tmp_cpus;
> > +     int tmp_len;
> > +     int i, j, k;
> > +     struct perf_cpu_map *merged = NULL;
> > +
> > +     if (perf_cpu_map__is_subset(other, orig))
> > +             return orig;
> > +     if (perf_cpu_map__is_subset(orig, other)) {
> > +             perf_cpu_map__put(orig);
>
> Why this put(orig)?

As with merge, if orig isn't returned then it is put.

> > +             return perf_cpu_map__get(other);
>
> And why the get here and not on the first if?

The first argument orig is either put or returned while the second may
be returned only if the reference count is incremented. We could
change the API for merge and intersect to put both arguments, or to
not put either argument.

Thanks,
Ian

> > +     }
> > +
> > +     tmp_len = max(orig->nr, other->nr);
> > +     tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
> > +     if (!tmp_cpus)
> > +             return NULL;
> > +
> > +     i = j = k = 0;
> > +     while (i < orig->nr && j < other->nr) {
> > +             if (orig->map[i].cpu < other->map[j].cpu)
> > +                     i++;
> > +             else if (orig->map[i].cpu > other->map[j].cpu)
> > +                     j++;
> > +             else {
> > +                     j++;
> > +                     tmp_cpus[k++] = orig->map[i++];
> > +             }
> > +     }
> > +     if (k)
> > +             merged = cpu_map__trim_new(k, tmp_cpus);
> > +     free(tmp_cpus);
> > +     perf_cpu_map__put(orig);
> > +     return merged;
> > +}
> > diff --git a/tools/lib/perf/include/perf/cpumap.h b/tools/lib/perf/include/perf/cpumap.h
> > index 4a2edbdb5e2b..a2a7216c0b78 100644
> > --- a/tools/lib/perf/include/perf/cpumap.h
> > +++ b/tools/lib/perf/include/perf/cpumap.h
> > @@ -19,6 +19,8 @@ LIBPERF_API struct perf_cpu_map *perf_cpu_map__read(FILE *file);
> >  LIBPERF_API struct perf_cpu_map *perf_cpu_map__get(struct perf_cpu_map *map);
> >  LIBPERF_API struct perf_cpu_map *perf_cpu_map__merge(struct perf_cpu_map *orig,
> >                                                    struct perf_cpu_map *other);
> > +LIBPERF_API struct perf_cpu_map *perf_cpu_map__intersect(struct perf_cpu_map *orig,
> > +                                                      struct perf_cpu_map *other);
> >  LIBPERF_API void perf_cpu_map__put(struct perf_cpu_map *map);
> >  LIBPERF_API struct perf_cpu perf_cpu_map__cpu(const struct perf_cpu_map *cpus, int idx);
> >  LIBPERF_API int perf_cpu_map__nr(const struct perf_cpu_map *cpus);
> > --
> > 2.35.1.1021.g381101b075-goog
>
> --
>
> - Arnaldo