Messages in this thread | | | From | Namhyung Kim <> | Date | Thu, 29 Sep 2022 13:42:45 -0700 | Subject | Re: [PATCH 2/5] libperf: Propagate maps only if necessary |
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On Wed, Sep 28, 2022 at 10:19 PM Adrian Hunter <adrian.hunter@intel.com> wrote: > > On 29/09/22 08:09, Namhyung Kim wrote: > > On Wed, Sep 28, 2022 at 7:08 PM Ian Rogers <irogers@google.com> wrote: > >> > >> On Wed, Sep 28, 2022 at 4:46 PM Namhyung Kim <namhyung@kernel.org> wrote: > >>> > >>> On Wed, Sep 28, 2022 at 12:54 AM Adrian Hunter <adrian.hunter@intel.com> wrote: > >>>> > >>>> On 27/09/22 20:28, Namhyung Kim wrote: > >>>>> Hi Adrian, > >>>>> > >>>>> On Tue, Sep 27, 2022 at 12:06 AM Adrian Hunter <adrian.hunter@intel.com> wrote: > >>>>>> > >>>>>> On 24/09/22 19:57, Namhyung Kim wrote: > >>>>>>> The current code propagate evsel's cpu map settings to evlist when it's > >>>>>>> added to an evlist. But the evlist->all_cpus and each evsel's cpus will > >>>>>>> be updated in perf_evlist__set_maps() later. No need to do it before > >>>>>>> evlist's cpus are set actually. > >>>>>>> > >>>>>>> Actually we discarded this intermediate all_cpus maps at the beginning > >>>>>>> of perf_evlist__set_maps(). Let's not do this. It's only needed when > >>>>>>> an evsel is added after the evlist cpu maps are set. > >>>>>> > >>>>>> That might not be true. Consider evlist__fix_hybrid_cpus() which fiddles > >>>>>> with evsel->core.cpus and evsel->core.own_cpus after the evsel has been > >>>>>> added to the evlist. It can also remove an evsel from the evlist. > >>>>> > >>>>> Thanks for your review. I think it's fine to change evsel cpus or to remove > >>>>> an evsel from evlist before calling evlist__create_maps(). The function > >>>>> will take care of setting evlist's all_cpus from the evsels in the evlist. > >>>>> So previous changes in evsel/cpus wouldn't be any special. > >>>>> > >>>>> After this point, adding a new evsel needs to update evlist all cpus by > >>>>> propagating cpu maps. So I think hybrid cpus should be fine. > >>>>> Did I miss something? > >>>> > >>>> I wondered how it might play out if evlist__fix_hybrid_cpus() reduced the > >>>> cpus from the target->cpu_list (using perf record -C) , since after this > >>>> patch all_cpus always starts with the target->cpu_list instead of an empty > >>>> list. But then, in the hybrid case, it puts a dummy event that uses the > >>>> target cpu list anyway, so the result is the same. > >>>> > >>>> I don't know if there are any cases where all_cpus would actually need to > >>>> exclude some of the cpus from target->cpu_list. > >>> > >>> I'm not aware of other cases to reduce cpu list. I think it'd be fine > >>> if it has a cpu in the evlist->all_cpus even if it's not used. The evsel > >>> should have a correct list anyway and we mostly use the evsel cpus > >>> to do the real work. > >>> > >>> Thanks, > >>> Namhyung > >> > >> The affinity changes made it so that we use all_cpus probably more > >> often than the evsel CPU maps for real work. The reason being we want > >> to avoid IPIs so we do all the work on 1 CPU and then move to the next > >> CPU in evlist all_cpus. evsel CPU maps are used to make sure the > >> indices are kept accurate - for example, if an uncore event is > >> measured with a CPU event: > >> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/util/evlist.h?h=perf/core#n366 > >> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/util/evlist.c?h=perf/core#n404 > > > > Right, I meant it'd check the evsel cpus eventually even if it iterates > > on the evlist all_cpus. The evlist_cpu_iterator__next() will skip a > > CPU if it's not in the evsel cpus. > > > > Thanks, > > Namhyung > > Perhaps an alternative is to be explicit about deferring map > propagation e.g.
Thanks for your patch. Yeah, we can use this.
But I still think it'd be better doing it unconditionally since any propagation before perf_evlist__set_maps will be discarded anyway. With this change, other than perf record will collect all cpus before _set_maps and then discard it. It seems like a waste, no?
Or else, we can have allow_map_propagation initialized to false and set it to true in perf_evlist__set_maps().
Thanks, Namhyung
> > diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c > index 19eaea99aa4f..5ce19e62397d 100644 > --- a/tools/lib/perf/evlist.c > +++ b/tools/lib/perf/evlist.c > @@ -70,6 +70,7 @@ static void perf_evlist__propagate_maps(struct perf_evlist *evlist) > /* Recomputing all_cpus, so start with a blank slate. */ > perf_cpu_map__put(evlist->all_cpus); > evlist->all_cpus = NULL; > + evlist->defer_map_propagation = false; > > perf_evlist__for_each_evsel(evlist, evsel) > __perf_evlist__propagate_maps(evlist, evsel); > @@ -81,7 +82,8 @@ void perf_evlist__add(struct perf_evlist *evlist, > evsel->idx = evlist->nr_entries; > list_add_tail(&evsel->node, &evlist->entries); > evlist->nr_entries += 1; > - __perf_evlist__propagate_maps(evlist, evsel); > + if (!evlist->defer_map_propagation) > + __perf_evlist__propagate_maps(evlist, evsel); > } > > void perf_evlist__remove(struct perf_evlist *evlist, > @@ -177,9 +179,6 @@ void perf_evlist__set_maps(struct perf_evlist *evlist, > evlist->threads = perf_thread_map__get(threads); > } > > - if (!evlist->all_cpus && cpus) > - evlist->all_cpus = perf_cpu_map__get(cpus); > - > perf_evlist__propagate_maps(evlist); > } > > diff --git a/tools/lib/perf/include/internal/evlist.h b/tools/lib/perf/include/internal/evlist.h > index 6f89aec3e608..dbe0b763f597 100644 > --- a/tools/lib/perf/include/internal/evlist.h > +++ b/tools/lib/perf/include/internal/evlist.h > @@ -19,6 +19,7 @@ struct perf_evlist { > int nr_entries; > int nr_groups; > bool has_user_cpus; > + bool defer_map_propagation; > /** > * The cpus passed from the command line or all online CPUs by > * default. > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > index 52d254b1530c..1c2523d66a14 100644 > --- a/tools/perf/builtin-record.c > +++ b/tools/perf/builtin-record.c > @@ -3975,6 +3975,7 @@ int cmd_record(int argc, const char **argv) > rec->evlist = evlist__new(); > if (rec->evlist == NULL) > return -ENOMEM; > + rec->evlist->core.defer_map_propagation = true; > > err = perf_config(perf_record_config, rec); > if (err) >
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