Re: [PATCH V2 21/23] libperf evsel: Add comments for booleans

Adrian Hunter
2022-05-11T07:04:49Z

On 6/05/22 23:51, Ian Rogers wrote:
> On Fri, May 6, 2022 at 5:26 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>
>> Add comments for 'system_wide' and 'requires_cpu' booleans
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>> ---
>> tools/lib/perf/include/internal/evsel.h | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/tools/lib/perf/include/internal/evsel.h b/tools/lib/perf/include/internal/evsel.h
>> index 77fbb8b97e5c..cc8f1ba790bd 100644
>> --- a/tools/lib/perf/include/internal/evsel.h
>> +++ b/tools/lib/perf/include/internal/evsel.h
>> @@ -49,7 +49,16 @@ struct perf_evsel {
>>
>> /* parse modifier helper */
>> int nr_members;
>> + /*
>> + * system_wide is for events that need to be on every CPU, irrespective
>> + * of user requested CPUs or threads. Map propagation will not override
>> + * this events own_cpus, which will contribute to evlist all_cpus.
>
> So this muddies my understanding of cpus and own_cpus (sigh, again
> undocumented). I believe cpus to be the set of CPUs (or any CPU, aka
> dummy) that perf_event_open happens on. all_cpus in evlist is the
> union of all the evsels cpus (ie not related to own_cpus as described
> here). Own_cpus I believe to be what's computed at parse-event time
> from sysfs. Is this a typo in the comment or quite likely my error?

A 'system_wide' event is not created by the parser, so own_cpus is set
by the code adding the event.

>
> Thanks,
> Ian
>
>> + */
>> bool system_wide;
>> + /*
>> + * Some events, for example uncore events, require a CPU.
>> + * i.e. it cannot be the 'any CPU' value of -1.
>> + */
>> bool requires_cpu;
>> int idx;
>> };
>> --
>> 2.25.1
>>