linux-kernel - Re: [PATCH] perf evsel: Ignore the non-group case for branch counters

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Message-ID: <CAP-5=fXGavfHvSPs5dRWmS93gspj4uUE6ftd855xFyN-hKRTzg@mail.gmail.com>
Date:   Mon, 13 Nov 2023 07:49:56 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, jolsa@...nel.org, namhyung@...nel.org,
        adrian.hunter@...el.com, tinghao.zhang@...el.com,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH] perf evsel: Ignore the non-group case for branch counters

On Thu, Nov 9, 2023 at 8:41 AM <kan.liang@...ux.intel.com> wrote:
>
> From: Kan Liang <kan.liang@...ux.intel.com>
>
> The perf test 27: Sample parsing fails with the branch counters support
> introduced.
>
> The branch counters feature requires all the events to belong to a
> group. There is no problem with the normal perf usage which usually
> initializes an evlist even for a single evsel.
> But the perf test is special, which may not initialize an evlist. The
> Sample parsing test case is one of the examples. The existing code
> crashes with the !evsel->evlist.
>
> Non-group means the evsel doesn't have branch counters support.

Thanks Kan, do we need to add this condition to
parse_events__sort_events_and_fix_groups?
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/parse-events.c#n2174

Ian

> Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> Closes: https://lore.kernel.org/lkml/ZUv+G+w5EvJgQS45@kernel.org/
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
>  tools/perf/util/evsel.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 58a9b8c82790..7a6a2d1f96db 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2355,6 +2355,10 @@ static inline bool evsel__has_branch_counters(const struct evsel *evsel)
>  {
>         struct evsel *cur, *leader = evsel__leader(evsel);
>
> +       /* The branch counters feature only supports group */
> +       if (!leader || !evsel->evlist)
> +               return false;
> +
>         evlist__for_each_entry(evsel->evlist, cur) {
>                 if ((leader == evsel__leader(cur)) &&
>                     (cur->core.attr.branch_sample_type & PERF_SAMPLE_BRANCH_COUNTERS))
> --
> 2.35.1
>