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Date: Wed, 4 May 2022 15:54:17 +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 v5 4/6] perf cpumap: Handle dummy maps as empty in subset
On 3/05/22 17:03, Ian Rogers wrote:
> On Tue, May 3, 2022 at 12:43 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> On 3/05/22 07:17, Ian Rogers wrote:
>>> perf_cpu_map__empty is true for empty and dummy maps. Make is_subset
>>> respect that.
>>
>> As I wrote before, I am not keen on this because it prevents -1, as a
>> valid 3rd parameter to perf_event_open(), from being represented
>> in merged evsel cpu maps.
>>
>> Why do you want this?
>
> Thanks Adrian, could you give me a test case (command line) where the
> differing dummy and empty behavior matters?
perf record --per-thread -e intel_pt// uname
With patchset "perf intel-pt: Better support for perf record --cpu"
the above will have (assuming 8-CPUs):
user_requested_cpus = {-1}
intel_pt evsel->cpus = {-1}
text_poke dummy evsel->cpus = {0-7}
which when merged would result in:
before this patch: all_cpus = {-1-7}
after this patch: all_cpus = {0-7}
The absence of -1 will mean that the intel_pt event does not get
mmapped.
> Normally cpus/own_cpus are
> set to null during parsing. They may get replaced with
> user_requested_cpus:
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/lib/perf/evlist.c?h=perf/core#n44
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/lib/perf/evlist.c?h=perf/core#n45
> (should it be on line 45 that !empty is expected?)
>
> During merge the null/empty all_cpus drops this value, which doesn't
> matter as the behavior with empty is the same as dummy:
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/lib/perf/evsel.c?h=perf/core#n119
>
> What's concerning me is the definition of empty:
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/lib/perf/cpumap.c?h=perf/core#n279
> ```
> return map ? map->map[0].cpu == -1 : true;
> ```
> If the first entry can be -1 and there can be other CPUs merged after
> then that cpu map will be empty by the definition above. Perhaps it
> should be:
> ```
> return map ? (map->nr == 1 && map->map[0].cpu == -1) : true;
> ```
> but it seems you prefer:
> ```
> return (map == NULL) ? true : false;
> ```
>
> You'd asked what the behavior with a dummy is and clearly it is
> somewhat muddy. That is what this patch and unit test is trying to
> clean up.
>
> 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;
>>> }
>>>
>>
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