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

[Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>]

On March 28, 2022 5:54:06 PM GMT-03:00, Ian Rogers <irogers@google.com> wrote:
>On Mon, Mar 28, 2022 at 1:28 PM Arnaldo Carvalho de Melo
><acme@kernel.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@google.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.

For merge I can see it dropping a reference, i.e. get b and merge it into a, after that b was "consumed"

But for intersect?


>
>> > +             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