linux-kernel - Re: [PATCH v2 2/7] perf evlist: Add evlist__findnew_tracking

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Date:   Wed, 19 Jul 2023 09:44:56 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Yang Jihong <yangjihong1@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, namhyung@...nel.org, adrian.hunter@...el.com,
        kan.liang@...ux.intel.com, james.clark@....com,
        tmricht@...ux.ibm.com, ak@...ux.intel.com,
        anshuman.khandual@....com, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 2/7] perf evlist: Add evlist__findnew_tracking_event() helper

On Fri, Jul 14, 2023 at 8:31 PM Yang Jihong <yangjihong1@...wei.com> wrote:
>
> Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
> tracking to the evlist. We may need to search for the dummy event for
> some settings. Therefore, add evlist__findnew_tracking_event() helper.
>
> evlist__findnew_tracking_event() also deal with system_wide maps if
> system_wide is true.

I'm wondering if we can simplify the naming in the API, we have "dummy
event" which makes sense as we literally call the event "dummy",
"sideband" which refers to the kind of samples/events the dummy event
will record but "tracking" I think tends to get used as a verb rather
than a noun. So I think evlist__findnew_tracking_event should be
evlist__findnew_dummy_event.

Thanks,
Ian

> Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
> ---
>  tools/perf/builtin-record.c | 11 +++--------
>  tools/perf/util/evlist.c    | 18 ++++++++++++++++++
>  tools/perf/util/evlist.h    |  1 +
>  3 files changed, 22 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index aec18db7ff23..ca83599cc50c 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1295,14 +1295,9 @@ static int record__open(struct record *rec)
>          */
>         if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
>             perf_pmus__num_core_pmus() > 1) {
> -               pos = evlist__get_tracking_event(evlist);
> -               if (!evsel__is_dummy_event(pos)) {
> -                       /* Set up dummy event. */
> -                       if (evlist__add_dummy(evlist))
> -                               return -ENOMEM;
> -                       pos = evlist__last(evlist);
> -                       evlist__set_tracking_event(evlist, pos);
> -               }
> +               pos = evlist__findnew_tracking_event(evlist, false);
> +               if (!pos)
> +                       return -ENOMEM;
>
>                 /*
>                  * Enable the dummy event when the process is forked for
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 7ef43f72098e..25c3ebe2c2f5 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1694,6 +1694,24 @@ void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_ev
>         tracking_evsel->tracking = true;
>  }
>
> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide)
> +{
> +       struct evsel *evsel;
> +
> +       evsel = evlist__get_tracking_event(evlist);
> +       if (!evsel__is_dummy_event(evsel)) {
> +               evsel = evlist__add_aux_dummy(evlist, system_wide);
> +               if (!evsel)
> +                       return NULL;
> +
> +               evlist__set_tracking_event(evlist, evsel);
> +       } else if (system_wide) {
> +               perf_evlist__go_system_wide(&evlist->core, &evsel->core);
> +       }
> +
> +       return evsel;
> +}
> +
>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str)
>  {
>         struct evsel *evsel;
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 664c6bf7b3e0..98e7ddb2bd30 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -387,6 +387,7 @@ bool evlist_cpu_iterator__end(const struct evlist_cpu_iterator *evlist_cpu_itr);
>
>  struct evsel *evlist__get_tracking_event(struct evlist *evlist);
>  void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_evsel);
> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide);
>
>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str);
>
> --
> 2.30.GIT
>