Messages in this thread | | | From | Ian Rogers <> | Date | Wed, 28 Sep 2022 19:07:43 -0700 | Subject | Re: [PATCH 2/5] libperf: Propagate maps only if necessary |
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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
Thanks, Ian
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