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References: <20240529064327.4080674-1-weilin.wang@intel.com> <20240529064327.4080674-4-weilin.wang@intel.com>
In-Reply-To: <20240529064327.4080674-4-weilin.wang@intel.com>
From: Namhyung Kim <namhyung@kernel.org>
Date: Thu, 30 May 2024 23:40:53 -0700
Message-ID: <CAM9d7cgSwZ3PU3H9VNvxQakocEZ_CQEqB9M1o3xTMdJ7F1sufQ@mail.gmail.com>
Subject: Re: [RFC PATCH v10 3/8] perf stat: Fork and launch perf record when
 perf stat needs to get retire latency value for a metric.
To: weilin.wang@intel.com
Cc: Ian Rogers <irogers@google.com>, Arnaldo Carvalho de Melo <acme@kernel.org>, 
	Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, 
	Alexander Shishkin <alexander.shishkin@linux.intel.com>, Jiri Olsa <jolsa@kernel.org>, 
	Adrian Hunter <adrian.hunter@intel.com>, Kan Liang <kan.liang@linux.intel.com>, 
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, 
	Perry Taylor <perry.taylor@intel.com>, Samantha Alt <samantha.alt@intel.com>, 
	Caleb Biggers <caleb.biggers@intel.com>
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On Tue, May 28, 2024 at 11:43=E2=80=AFPM <weilin.wang@intel.com> wrote:
>
> From: Weilin Wang <weilin.wang@intel.com>
>
> When retire_latency value is used in a metric formula, evsel would fork a=
 perf
> record process with "-e" and "-W" options. Perf record will collect requi=
red
> retire_latency values in parallel while perf stat is collecting counting =
values.
>
> At the point of time that perf stat stops counting, evsel would stop perf=
 record
> by sending sigterm signal to perf record process. Sampled data will be pr=
ocess
> to get retire latency value.
>
> Another thread is required to synchronize between perf stat and perf reco=
rd
> when we pass data through pipe.
>
> Signed-off-by: Weilin Wang <weilin.wang@intel.com>
> ---
[SNIP]
> +int tpebs_set_evsel(struct evsel *evsel, int cpu_map_idx, int thread)
> +{
> +       struct perf_counts_values *count;
> +       struct tpebs_retire_lat *t;
> +       bool found =3D false;
> +       __u64 val;
> +       int ret;
> +
> +       /* Non reitre_latency evsel should never enter this function. */
> +       if (!evsel__is_retire_lat(evsel))
> +               return -1;
> +
> +       ret =3D tpebs_stop();
> +       if (ret)
> +               return ret;
> +
> +       count =3D perf_counts(evsel->counts, cpu_map_idx, thread);
> +
> +       list_for_each_entry(t, &tpebs_results, nd) {
> +               if (!strcmp(t->tpebs_name, evsel->name) || !strcmp(t->tpe=
bs_name, evsel->metric_id)) {
> +                       found =3D true;
> +                       break;
> +               }
> +       }
> +
> +       /* Set ena and run to non-zero */
> +       count->ena =3D count->run =3D 1;
> +       count->lost =3D 0;
> +
> +       if (!found) {
> +               /*
> +                * Set default value or 0 when retire_latency for this ev=
ent is
> +                * not found from sampling data (enable_tpebs_recording n=
ot set
> +                * or 0 sample recorded).
> +                */
> +               val =3D 0;
> +               return 0;
> +       }
> +
> +       /*
> +        * Only set retire_latency value to the first CPU and thread.
> +        */
> +       if (cpu_map_idx =3D=3D 0 && thread =3D=3D 0) {
> +       /* Lost precision when casting from double to __u64. Any improvem=
ent? */

As I said before I think you can set t->val * 1000 and then
set the evsel->scale to 1e3 or 1e-3.

Thanks,
Namhyung


> +               val =3D t->val;
> +       } else
> +               val =3D 0;
> +
> +       count->val =3D val;
> +       return 0;
> +}
> +