Messages in this thread | | | From | Ian Rogers <> | Date | Wed, 11 May 2022 22:34:24 -0700 | Subject | Re: [PATCH V2 21/23] libperf evsel: Add comments for booleans |
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On Wed, May 11, 2022 at 12:03 AM Adrian Hunter <adrian.hunter@intel.com> wrote: > > 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.
I think I may be misreading the comment. Perhaps it should read:
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 event's own_cpus and own_cpus don't contribute to the evlist all_cpus.
It would be nice if there were a comment on own_cpus to explain its relationship to cpus and more broadly when it is used. Fwiw, the parse time copy is made here: https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/util/parse-events.c?h=perf/core#n367
I worry that if own_cpus should be used in place of cpus then iterators like evlist__for_each_cpu may need to handle this, and so they'd be broken currently.
Thanks, Ian
> > > > 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 > >> >
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