linux-kernel - Re: [PATCH v6 6/6] perf tools: Flush remaining samples w/o deferred callchains

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Message-ID: <CAP-5=fV5_jxOmZP1q3k88Cs9VXG_d9YW0qk8NoUFKgZgp1x73A@mail.gmail.com>
Date: Tue, 2 Dec 2025 15:15:53 -0800
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, James Clark <james.clark@...aro.org>, 
	Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org, 
	Steven Rostedt <rostedt@...dmis.org>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Indu Bhagat <indu.bhagat@...cle.com>, Jens Remus <jremus@...ux.ibm.com>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, linux-trace-kernel@...r.kernel.org, 
	bpf@...r.kernel.org
Subject: Re: [PATCH v6 6/6] perf tools: Flush remaining samples w/o deferred callchains

On Thu, Nov 20, 2025 at 3:48 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> It's possible that some kernel samples don't have matching deferred
> callchain records when the profiling session was ended before the
> threads came back to userspace.  Let's flush the samples before
> finish the session.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

Reviewed-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  tools/perf/util/session.c | 50 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
>
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index dc570ad47ccc2c63..4236503c8f6c1350 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1295,6 +1295,10 @@ struct deferred_event {
>         union perf_event *event;
>  };
>
> +/*
> + * This is called when a deferred callchain record comes up.  Find all matching
> + * samples, merge the callchains and process them.
> + */
>  static int evlist__deliver_deferred_callchain(struct evlist *evlist,
>                                               const struct perf_tool *tool,
>                                               union  perf_event *event,
> @@ -1345,6 +1349,42 @@ static int evlist__deliver_deferred_callchain(struct evlist *evlist,
>         return ret;
>  }
>
> +/*
> + * This is called at the end of the data processing for the session.  Flush the
> + * remaining samples as there's no hope for matching deferred callchains.
> + */
> +static int session__flush_deferred_samples(struct perf_session *session,
> +                                          const struct perf_tool *tool)
> +{
> +       struct evlist *evlist = session->evlist;
> +       struct machine *machine = &session->machines.host;
> +       struct deferred_event *de, *tmp;
> +       struct evsel *evsel;
> +       int ret = 0;
> +
> +       list_for_each_entry_safe(de, tmp, &evlist->deferred_samples, list) {
> +               struct perf_sample sample;
> +
> +               ret = evlist__parse_sample(evlist, de->event, &sample);
> +               if (ret < 0) {
> +                       pr_err("failed to parse original sample\n");
> +                       break;
> +               }
> +
> +               evsel = evlist__id2evsel(evlist, sample.id);
> +               ret = evlist__deliver_sample(evlist, tool, de->event,
> +                                            &sample, evsel, machine);
> +
> +               list_del(&de->list);
> +               free(de->event);
> +               free(de);
> +
> +               if (ret)
> +                       break;
> +       }
> +       return ret;
> +}
> +
>  static int machines__deliver_event(struct machines *machines,
>                                    struct evlist *evlist,
>                                    union perf_event *event,
> @@ -2038,6 +2078,9 @@ static int __perf_session__process_pipe_events(struct perf_session *session)
>  done:
>         /* do the final flush for ordered samples */
>         err = ordered_events__flush(oe, OE_FLUSH__FINAL);
> +       if (err)
> +               goto out_err;
> +       err = session__flush_deferred_samples(session, tool);
>         if (err)
>                 goto out_err;
>         err = auxtrace__flush_events(session, tool);
> @@ -2384,6 +2427,9 @@ static int __perf_session__process_events(struct perf_session *session)
>         if (err)
>                 goto out_err;
>         err = auxtrace__flush_events(session, tool);
> +       if (err)
> +               goto out_err;
> +       err = session__flush_deferred_samples(session, tool);
>         if (err)
>                 goto out_err;
>         err = perf_session__flush_thread_stacks(session);
> @@ -2506,6 +2552,10 @@ static int __perf_session__process_dir_events(struct perf_session *session)
>         if (ret)
>                 goto out_err;
>
> +       ret = session__flush_deferred_samples(session, tool);
> +       if (ret)
> +               goto out_err;
> +
>         ret = perf_session__flush_thread_stacks(session);
>  out_err:
>         ui_progress__finish();
> --
> 2.52.0.rc2.455.g230fcf2819-goog
>