Re: [PATCH V1 13/23] perf evlist: Add evlist__add_system_wide_dummy()

[Adrian Hunter <adrian.hunter@intel.com>]

On 6/05/22 02:56, Ian Rogers wrote:
> On Thu, May 5, 2022 at 9:57 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>
>> Add evlist__add_system_wide_dummy() to enable creating a system-wide dummy
>> event that sets up the system-wide maps before map propagation.
> 
> Perhaps this should be:
> evlist__add_dummy_on_all_online_cpus()

Ok, but offline isn't an option, so I'll drop 'online' from the name.

> my thoughts being that a system wide dummy sounds like the dummy CPU
> map, ie {-1} whilst what happens here is opening on all online CPUs
> {0-35} on a 36 hyperthread system. Note also that the libperf
> cpu_map__read_all_cpu_map code doesn't discover sysfs' mount properly,
> as done in:
> tools/lib/api/fs/fs.h
> Some tech debt.
> 
>> 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@intel.com>
>> ---
>>  tools/perf/util/evlist.c | 40 ++++++++++++++++++++++++++++++++++++++++
>>  tools/perf/util/evlist.h |  5 +++++
>>  2 files changed, 45 insertions(+)
>>
>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>> index 78c47cbafbc2..58ea562ddbd2 100644
>> --- a/tools/perf/util/evlist.c
>> +++ b/tools/perf/util/evlist.c
>> @@ -264,6 +264,46 @@ int evlist__add_dummy(struct evlist *evlist)
>>         return 0;
>>  }
>>
>> +static void evlist__add_system_wide(struct evlist *evlist, struct evsel *evsel)
> 
> This would be:
> evlist__add_on_all_online_cpus(..)
> 
>> +{
>> +       evsel->core.system_wide = true;
>> +
>> +       /* All 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);
>> +
>> +       /* 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_system_wide(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..dd1af114e033 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_system_wide_dummy(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
>>