linux-kernel - Re: [RFC PATCH v9 5/7] perf stat: Add command line option for enabling tpebs recording

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Date: Fri, 24 May 2024 16:20:47 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: weilin.wang@...el.com
Cc: Ian Rogers <irogers@...gle.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Perry Taylor <perry.taylor@...el.com>, Samantha Alt <samantha.alt@...el.com>, 
	Caleb Biggers <caleb.biggers@...el.com>
Subject: Re: [RFC PATCH v9 5/7] perf stat: Add command line option for
 enabling tpebs recording

On Tue, May 21, 2024 at 10:40 AM <weilin.wang@...el.com> wrote:
>
> From: Weilin Wang <weilin.wang@...el.com>
>
> With this command line option, tpebs recording is turned off in perf stat on
> default. It will only be turned on when this option is given in perf stat
> command.
>
> Signed-off-by: Weilin Wang <weilin.wang@...el.com>
> ---
>  tools/perf/builtin-stat.c | 19 +++++++++++++------
>  tools/perf/util/evsel.c   | 19 ++++++++++++++-----
>  2 files changed, 27 insertions(+), 11 deletions(-)
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index c0e9dfa3b3c2..c27521fb1aee 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -117,6 +117,7 @@ static volatile sig_atomic_t        child_pid                       = -1;
>  static int                     detailed_run                    =  0;
>  static bool                    transaction_run;
>  static bool                    topdown_run                     = false;
> +static bool                    tpebs_recording                 = false;
>  static bool                    smi_cost                        = false;
>  static bool                    smi_reset                       = false;
>  static int                     big_num_opt                     =  -1;
> @@ -677,9 +678,11 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>         int err;
>         bool second_pass = false;
>
> -       err = start_tpebs(&stat_config, evsel_list);
> -       if (err < 0)
> -               return err;
> +       if (tpebs_recording) {
> +               err = start_tpebs(&stat_config, evsel_list);
> +               if (err < 0)
> +                       return err;
> +       }
>
>         if (forks) {
>                 if (evlist__prepare_workload(evsel_list, &target, argv, is_pipe, workload_exec_failed_signal) < 0) {
> @@ -886,9 +889,11 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>
>         t1 = rdclock();
>
> -       err = stop_tpebs();
> -       if (err < 0)
> -               return err;
> +       if (tpebs_recording) {
> +               err = stop_tpebs();
> +               if (err < 0)
> +                       return err;
> +       }
>
>         if (stat_config.walltime_run_table)
>                 stat_config.walltime_run[run_idx] = t1 - t0;
> @@ -1246,6 +1251,8 @@ static struct option stat_options[] = {
>                        "disable adding events for the metric threshold calculation"),
>         OPT_BOOLEAN(0, "topdown", &topdown_run,
>                         "measure top-down statistics"),
> +       OPT_BOOLEAN(0, "enable-tpebs-recording", &tpebs_recording,

Just --tpebs or --tpebs-record?  I just prefer short names. :)


> +                       "enable recording for tpebs when retire_latency required"),
>         OPT_UINTEGER(0, "td-level", &stat_config.topdown_level,
>                         "Set the metrics level for the top-down statistics (0: max level)"),
>         OPT_BOOLEAN(0, "smi-cost", &smi_cost,
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 4d700338fc99..e1f3f63dfb54 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1540,21 +1540,30 @@ static int evsel__set_retire_lat(struct evsel *evsel, int cpu_map_idx, int threa
>                 }
>         }
>
> -       if (!found)
> -               return -1;
> +       /* Set ena and run to non-zero */
> +       count->ena = count->run = 1;
> +       count->lost = 0;
> +
> +       if (!found) {
> +               /*
> +                * Set default value or 0 when retire_latency for this event is
> +                * not found from sampling data (enable_tpebs_recording not set
> +                * or 0 sample recorded).
> +                */
> +               val = 0;
> +               return 0;
> +       }
>
>         /*
>          * Only set retire_latency value to the first CPU and thread.
>          */
>         if (cpu_map_idx == 0 && thread == 0)
> +       /* Lost precision when casting from double to __u64. Any improvement? */

Maybe you can save val * 1000 and then later
convert back to double and divide by 1000?

Thanks,
Namhyung


>                 val = t->val;
>         else
>                 val = 0;
>
>         count->val = val;
> -       /* Set ena and run to non-zero */
> -       count->ena = count->run = 1;
> -       count->lost = 0;
>         return 0;
>  }
>
> --
> 2.43.0
>