linux-kernel - Re: [PATCH 2/5] perf evlist: Add evlist__findnew_tracking

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Date:   Tue, 11 Jul 2023 16:13:08 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Yang Jihong <yangjihong1@...wei.com>, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, irogers@...gle.com, kan.liang@...ux.intel.com,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 2/5] perf evlist: Add evlist__findnew_tracking_event()
 helper

On 4/07/23 10:42, Yang Jihong 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.
> 
> Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
> ---
>  tools/perf/builtin-record.c | 11 +++--------
>  tools/perf/util/evlist.c    | 17 +++++++++++++++++
>  tools/perf/util/evlist.h    |  1 +
>  3 files changed, 21 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index aec18db7ff23..8872cd037f2c 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);
> +		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..4621ddaeb8f3 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1694,6 +1694,23 @@ 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)
> +{
> +	struct evsel *evsel;
> +
> +	evsel = evlist__get_tracking_event(evlist);
> +	if (!evsel__is_dummy_event(evsel)) {
> +		/* Set up dummy event. */
> +		if (evlist__add_dummy(evlist))

evlist__add_dummy() does not exclude_kernel so it
will end up relying on evsel__fallback() to work in
cases where the user does not have kernel access.

evlist__add_aux_dummy() is probably better suited.
Consequently perhaps pass system_wide as
a parameter to evlist__findnew_tracking_event() and
deal with that all inside evlist__findnew_tracking_event()

> +			return NULL;
> +
> +		evsel = evlist__last(evlist);
> +		evlist__set_tracking_event(evlist, evsel);
> +	}
> +
> +	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..4d28c50ba842 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);
>  
>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str);
>