linux-kernel - Re: [PATCH v4 4/6] perf cpumap: Handle dummy maps as empty in subset

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Message-ID: <5e8cd38c-1384-ed7e-3f92-f7e5f7c1578b@intel.com>
Date:   Tue, 3 May 2022 07:51:50 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        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>,
        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,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v4 4/6] perf cpumap: Handle dummy maps as empty in subset

On 2/05/22 20:04, Ian Rogers wrote:
> On Mon, May 2, 2022 at 9:13 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> On 30/04/22 09:23, Ian Rogers wrote:
>>> perf_cpu_map__empty is true for empty and dummy maps. Make is_subset
>>> respect that.
>>
>> I think this might be the opposite of what I am trying to do, which is
>> enable all_cpus to represent all the "cpu" values (3rd parameter of
>> perf_event_open()) to iterate over including -1 so that per-thread and
>> per-cpu events can be mixed.
> 
> Wouldn't you iterate over the cpus of the evsel?

When mmapping perf events, it is necessary to iterate all (user_requested)
cpus / threads in order to conveniently set-output events on the same
cpu / thread.

>                                                  I'm not sure using
> all_cpus in that way makes sense

It does if you want to mix per-cpu and per-thread (cpu == -1) events.
As I wrote previously, the cpus is then seen as a list of values for
parameter 3 of perf_event_open(), and therefore includes -1.

>                                   it also violates the definition of
> empty.

That can be renamed, since it is typically being used to mean
per-thread (i.e. per-task context)

> 
> Thanks,
> Ian
> 
>>>
>>> Signed-off-by: Ian Rogers <irogers@...gle.com>
>>> ---
>>>  tools/lib/perf/cpumap.c   |  4 ++--
>>>  tools/perf/tests/cpumap.c | 10 +++++++++-
>>>  2 files changed, 11 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
>>> index 384d5e076ee4..9c83675788c2 100644
>>> --- a/tools/lib/perf/cpumap.c
>>> +++ b/tools/lib/perf/cpumap.c
>>> @@ -322,9 +322,9 @@ struct perf_cpu perf_cpu_map__max(struct perf_cpu_map *map)
>>>  /** Is 'b' a subset of 'a'. */
>>>  bool perf_cpu_map__is_subset(const struct perf_cpu_map *a, const struct perf_cpu_map *b)
>>>  {
>>> -     if (a == b || !b)
>>> +     if (a == b || perf_cpu_map__empty(b))
>>>               return true;
>>> -     if (!a || b->nr > a->nr)
>>> +     if (perf_cpu_map__empty(a) || b->nr > a->nr)
>>>               return false;
>>>
>>>       for (int i = 0, j = 0; i < a->nr; i++) {
>>> diff --git a/tools/perf/tests/cpumap.c b/tools/perf/tests/cpumap.c
>>> index f94929ebb54b..d52b58395385 100644
>>> --- a/tools/perf/tests/cpumap.c
>>> +++ b/tools/perf/tests/cpumap.c
>>> @@ -128,13 +128,21 @@ static int test__cpu_map_merge(struct test_suite *test __maybe_unused, int subte
>>>       struct perf_cpu_map *a = perf_cpu_map__new("4,2,1");
>>>       struct perf_cpu_map *b = perf_cpu_map__new("4,5,7");
>>>       struct perf_cpu_map *c = perf_cpu_map__merge(a, b);
>>> +     struct perf_cpu_map *d = perf_cpu_map__dummy_new();
>>> +     struct perf_cpu_map *e = perf_cpu_map__merge(b, d);
>>>       char buf[100];
>>>
>>>       TEST_ASSERT_VAL("failed to merge map: bad nr", perf_cpu_map__nr(c) == 5);
>>>       cpu_map__snprint(c, buf, sizeof(buf));
>>>       TEST_ASSERT_VAL("failed to merge map: bad result", !strcmp(buf, "1-2,4-5,7"));
>>> -     perf_cpu_map__put(b);
>>> +
>>> +     TEST_ASSERT_VAL("failed to merge map: bad nr", perf_cpu_map__nr(e) == 3);
>>> +     cpu_map__snprint(e, buf, sizeof(buf));
>>> +     TEST_ASSERT_VAL("failed to merge map: bad result", !strcmp(buf, "4-5,7"));
>>> +
>>>       perf_cpu_map__put(c);
>>> +     perf_cpu_map__put(d);
>>> +     perf_cpu_map__put(e);
>>>       return 0;
>>>  }
>>>
>>