linux-kernel - Re: [PATCH 2/5] perf stat: Add --for-each-cgroup option

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Date:   Wed, 23 Sep 2020 07:51:33 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH 2/5] perf stat: Add --for-each-cgroup option

On Wed, Sep 23, 2020 at 6:40 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Mon, Sep 21, 2020 at 06:46:07PM +0900, Namhyung Kim wrote:
>
> SNIP
>
> > +int evlist__expand_cgroup(struct evlist *evlist, const char *str)
> > +{
> > +     struct evlist *orig_list, *tmp_list;
> > +     struct evsel *pos, *evsel, *leader;
> > +     struct cgroup *cgrp = NULL;
> > +     const char *p, *e, *eos = str + strlen(str);
> > +     int ret = -1;
> > +
> > +     if (evlist->core.nr_entries == 0) {
> > +             fprintf(stderr, "must define events before cgroups\n");
> > +             return -EINVAL;
> > +     }
> > +
> > +     orig_list = evlist__new();
> > +     tmp_list = evlist__new();
> > +     if (orig_list == NULL || tmp_list == NULL) {
> > +             fprintf(stderr, "memory allocation failed\n");
> > +             return -ENOMEM;
> > +     }
> > +
> > +     /* save original events and init evlist */
> > +     perf_evlist__splice_list_tail(orig_list, &evlist->core.entries);
> > +     evlist->core.nr_entries = 0;
> > +
> > +     for (;;) {
> > +             p = strchr(str, ',');
> > +             e = p ? p : eos;
> > +
> > +             /* allow empty cgroups, i.e., skip */
> > +             if (e - str) {
> > +                     /* termination added */
> > +                     char *name = strndup(str, e - str);
> > +                     if (!name)
> > +                             goto out_err;
> > +
> > +                     cgrp = cgroup__new(name);
> > +                     free(name);
> > +                     if (cgrp == NULL)
> > +                             goto out_err;
> > +             } else {
> > +                     cgrp = NULL;
> > +             }
> > +
> > +             leader = NULL;
> > +             evlist__for_each_entry(orig_list, pos) {
> > +                     evsel = evsel__clone(pos);
> > +                     if (evsel == NULL)
> > +                             goto out_err;
> > +
> > +                     cgroup__put(evsel->cgrp);
> > +                     evsel->cgrp = cgroup__get(cgrp);
> > +
> > +                     if (evsel__is_group_leader(pos))
> > +                             leader = evsel;
> > +                     evsel->leader = leader;
>
> hum, will this work if there's standalone event after group? like:
>
>   {cycles,instructions},cache-misses
>
> cache-misses will get cycles as group leader no?

AFAIK non-group events are treated as a leader of its own group.
So evsel__is_group_leader() will return true for cache-misses.

Thanks
Namhyung

>
> > +
> > +                     evlist__add(tmp_list, evsel);
> > +             }
> > +             /* cgroup__new() has a refcount, release it here */
> > +             cgroup__put(cgrp);
> > +             nr_cgroups++;
>
> SNIP
>