linux-kernel - Re: [PATCH] perf parse-events: Do not break up AUX event group

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Date:   Fri, 5 May 2023 06:02:41 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf parse-events: Do not break up AUX event group

On Thu, May 4, 2023 at 11:45 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> Assume AUX event group is correct and not do break it up.
>
> Example:
>
>  Before:
>
>     $ perf record --no-bpf-event -c 10 -e '{intel_pt//,tlb_flush.stlb_any/aux-sample-size=8192/pp}:u' -- sleep 0.1

Could we add this, or similar, to the intel_pt tests?

>     WARNING: events were regrouped to match PMUs
>     Cannot add AUX area sampling to a group leader
>
>  After:
>
>     $ perf record --no-bpf-event -c 10 -e '{intel_pt//,tlb_flush.stlb_any/aux-sample-size=8192/pp}:u' -- sleep 0.1
>     [ perf record: Woken up 1 times to write data ]
>     [ perf record: Captured and wrote 0.078 MB perf.data ]
>     $ perf script -F-dso,+addr | grep -C5 tlb_flush.stlb_any | head -11
>     sleep 20444 [003]  7939.510243:  1  branches:uH:  7f5350cc82a2 dl_main+0x9a2 => 7f5350cb38f0 _dl_add_to_namespace_list+0x0
>     sleep 20444 [003]  7939.510243:  1  branches:uH:  7f5350cb3908 _dl_add_to_namespace_list+0x18 => 7f5350cbb080 rtld_mutex_dummy+0x0
>     sleep 20444 [003]  7939.510243:  1  branches:uH:  7f5350cc8350 dl_main+0xa50 => 0 [unknown]
>     sleep 20444 [003]  7939.510244:  1  branches:uH:  7f5350cc83ca dl_main+0xaca => 7f5350caeb60 _dl_process_pt_gnu_property+0x0
>     sleep 20444 [003]  7939.510245:  1  branches:uH:  7f5350caeb60 _dl_process_pt_gnu_property+0x0 => 0 [unknown]
>     sleep 20444  7939.510245:       10 tlb_flush.stlb_any/aux-sample-size=8192/pp: 0 7f5350caeb60 _dl_process_pt_gnu_property+0x0
>     sleep 20444 [003]  7939.510254:  1  branches:uH:  7f5350cc87fe dl_main+0xefe => 7f5350ccd240 strcmp+0x0
>     sleep 20444 [003]  7939.510254:  1  branches:uH:  7f5350cc8862 dl_main+0xf62 => 0 [unknown]
>     sleep 20444 [003]  7939.510255:  1  branches:uH:  7f5350cc9cdc dl_main+0x23dc => 0 [unknown]
>     sleep 20444 [003]  7939.510257:  1  branches:uH:  7f5350cc89f6 dl_main+0x10f6 => 7f5350cb9530 _dl_setup_hash+0x0
>     sleep 20444 [003]  7939.510257:  1  branches:uH:  7f5350cc8a2d dl_main+0x112d => 7f5350cb3990 _dl_new_object+0x0
>
> Fixes: 347c2f0a0988 ("perf parse-events: Sort and group parsed events")
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>

These changes are related:
https://lore.kernel.org/lkml/20230502223851.2234828-5-irogers@google.com/
https://lore.kernel.org/lkml/20230502223851.2234828-20-irogers@google.com/

> ---
>  tools/perf/util/evsel.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 356c07f03be6..a34f61a5271d 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -828,7 +828,11 @@ bool evsel__name_is(struct evsel *evsel, const char *name)
>
>  const char *evsel__group_pmu_name(const struct evsel *evsel)
>  {
> -       const struct evsel *leader;
> +       const struct evsel *leader = evsel__leader(evsel);
> +
> +       /* Never break AUX event groups */
> +       if (evsel__is_aux_event(leader))
> +               return leader->pmu_name;
>
>         /* If the pmu_name is set use it. pmu_name isn't set for CPU and software events. */

I think this comment isn't true, hence this patch. I think we should
just move the check into the return, so:
return evsel->pmu_name ?: "cpu";

Sorry for the breakage!

Thanks,
Ian

>         if (evsel->pmu_name)
> @@ -837,15 +841,9 @@ const char *evsel__group_pmu_name(const struct evsel *evsel)
>          * Software events may be in a group with other uncore PMU events. Use
>          * the pmu_name of the group leader to avoid breaking the software event
>          * out of the group.
> -        *
> -        * Aux event leaders, like intel_pt, expect a group with events from
> -        * other PMUs, so substitute the AUX event's PMU in this case.
>          */
> -       leader  = evsel__leader(evsel);
> -       if ((evsel->core.attr.type == PERF_TYPE_SOFTWARE || evsel__is_aux_event(leader)) &&
> -           leader->pmu_name) {
> +       if (evsel->core.attr.type == PERF_TYPE_SOFTWARE && leader->pmu_name)
>                 return leader->pmu_name;
> -       }
>
>         return "cpu";
>  }
> --
> 2.34.1
>