linux-kernel - Re: [PATCH V3 13/23] perf evlist: Add evlist__add_dummy_on_all

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Date:   Thu, 12 May 2022 07:33:05 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ian Rogers <irogers@...gle.com>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>,
        Leo Yan <leo.yan@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 13/23] perf evlist: Add evlist__add_dummy_on_all_cpus()

On 12/05/22 01:50, Namhyung Kim wrote:
> On Wed, May 11, 2022 at 12:02 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> Add evlist__add_dummy_on_all_cpus() to enable creating a system-wide dummy
>> event that sets up the system-wide maps before map propagation.
>>
>> For convenience, add evlist__add_aux_dummy() so that the logic can be used
>> whether or not the event needs to be system-wide.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>> ---
>>
>> Changes in V3: Amended comment about all CPUs.
>>
>>  tools/perf/util/evlist.c | 45 ++++++++++++++++++++++++++++++++++++++++
>>  tools/perf/util/evlist.h |  5 +++++
>>  2 files changed, 50 insertions(+)
>>
>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>> index 78c47cbafbc2..2b2900434bba 100644
>> --- a/tools/perf/util/evlist.c
>> +++ b/tools/perf/util/evlist.c
>> @@ -264,6 +264,51 @@ int evlist__add_dummy(struct evlist *evlist)
>>         return 0;
>>  }
>>
>> +static void evlist__add_on_all_cpus(struct evlist *evlist, struct evsel *evsel)
>> +{
>> +       evsel->core.system_wide = true;
>> +
>> +       /*
>> +        * All CPUs.
>> +        *
>> +        * Note perf_event_open() does not accept CPUs that are not online, so
>> +        * in fact this CPU list will include only all online CPUs.
>> +        */
>> +       perf_cpu_map__put(evsel->core.own_cpus);
>> +       evsel->core.own_cpus = perf_cpu_map__new(NULL);
>> +       perf_cpu_map__put(evsel->core.cpus);
>> +       evsel->core.cpus = perf_cpu_map__get(evsel->core.own_cpus);
> 
> Maybe I'm missing something.. Wouldn't it be overwritten
> by the user requested cpus during map propagation in
> evlist__add()?

Yes.  That gets changed in patch 22 "perf tools: Allow system-wide
events to keep their own CPUs"

> 
> Thanks,
> Namhyung
> 
> 
>> +
>> +       /* No threads */
>> +       perf_thread_map__put(evsel->core.threads);
>> +       evsel->core.threads = perf_thread_map__new_dummy();
>> +
>> +       evlist__add(evlist, evsel);
>> +}
>> +
>> +struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide)
>> +{
>> +       struct evsel *evsel = evlist__dummy_event(evlist);
>> +
>> +       if (!evsel)
>> +               return NULL;
>> +
>> +       evsel->core.attr.exclude_kernel = 1;
>> +       evsel->core.attr.exclude_guest = 1;
>> +       evsel->core.attr.exclude_hv = 1;
>> +       evsel->core.attr.freq = 0;
>> +       evsel->core.attr.sample_period = 1;
>> +       evsel->no_aux_samples = true;
>> +       evsel->name = strdup("dummy:u");
>> +
>> +       if (system_wide)
>> +               evlist__add_on_all_cpus(evlist, evsel);
>> +       else
>> +               evlist__add(evlist, evsel);
>> +
>> +       return evsel;
>> +}
>> +
>>  static int evlist__add_attrs(struct evlist *evlist, struct perf_event_attr *attrs, size_t nr_attrs)
>>  {
>>         struct evsel *evsel, *n;
>> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
>> index 4062f5aebfc1..1bde9ccf4e7d 100644
>> --- a/tools/perf/util/evlist.h
>> +++ b/tools/perf/util/evlist.h
>> @@ -114,6 +114,11 @@ int arch_evlist__add_default_attrs(struct evlist *evlist);
>>  struct evsel *arch_evlist__leader(struct list_head *list);
>>
>>  int evlist__add_dummy(struct evlist *evlist);
>> +struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide);
>> +static inline struct evsel *evlist__add_dummy_on_all_cpus(struct evlist *evlist)
>> +{
>> +       return evlist__add_aux_dummy(evlist, true);
>> +}
>>
>>  int evlist__add_sb_event(struct evlist *evlist, struct perf_event_attr *attr,
>>                          evsel__sb_cb_t cb, void *data);
>> --
>> 2.25.1
>>