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From: Namhyung Kim <namhyung@kernel.org>
Date: Tue, 23 Apr 2024 16:05:48 -0700
Message-ID: <CAM9d7chSCQViX=VjgqdVn5un0J5MpGsGDGncUyY-K4=oPvvfQA@mail.gmail.com>
Subject: Re: [RFC PATCH v6 2/5] perf stat: Fork and launch perf record when
 perf stat needs to get retire latency value for a metric.
To: "Wang, Weilin" <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>, 
	"Hunter, Adrian" <adrian.hunter@intel.com>, Kan Liang <kan.liang@linux.intel.com>, 
	"linux-perf-users@vger.kernel.org" <linux-perf-users@vger.kernel.org>, 
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "Taylor, Perry" <perry.taylor@intel.com>, 
	"Alt, Samantha" <samantha.alt@intel.com>, "Biggers, Caleb" <caleb.biggers@intel.com>
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On Tue, Apr 23, 2024 at 3:16=E2=80=AFPM Wang, Weilin <weilin.wang@intel.com=
> wrote:
> > > > > -static int __run_perf_record(void)
> > > > > +static int __run_perf_record(const char **record_argv)
> > > > >  {
> > > > > +       int i =3D 0;
> > > > > +       struct tpebs_event *e;
> > > > > +
> > > > >         pr_debug("Prepare perf record for retire_latency\n");
> > > > > +
> > > > > +       record_argv[i++] =3D "perf";
> > > > > +       record_argv[i++] =3D "record";
> > > > > +       record_argv[i++] =3D "-W";
> > > > > +       record_argv[i++] =3D "--synth=3Dno";
> > > > > +
> > > > > +       if (stat_config.user_requested_cpu_list) {
> > > > > +               record_argv[i++] =3D "-C";
> > > > > +               record_argv[i++] =3D stat_config.user_requested_c=
pu_list;
> > > > > +       }
> > > > > +
> > > > > +       if (stat_config.system_wide)
> > > > > +               record_argv[i++] =3D "-a";
> > > > > +
> > > > > +       if (!stat_config.system_wide
> > && !stat_config.user_requested_cpu_list)
> > > > {
> > > > > +               pr_err("Require -a or -C option to run sampling.\=
n");
> > > > > +               return -ECANCELED;
> > > > > +       }
> > > > > +
> > > > > +       list_for_each_entry(e, &stat_config.tpebs_events, nd) {
> > > > > +               record_argv[i++] =3D "-e";
> > > > > +               record_argv[i++] =3D e->name;
> > > > > +       }
> > > > > +
> > > > > +       record_argv[i++] =3D "-o";
> > > > > +       record_argv[i++] =3D PERF_DATA;
> > > > > +
> > > > >         return 0;
> > > > >  }
> > > >
> > > > Still I think it's weird it has 'perf record' in perf stat (despite=
 the
> > > > 'perf stat record').  If it's only Intel thing and we don't have a =
plan
> > > > to do the same on other arches, we can move it to the arch
> > > > directory and keep the perf stat code simple.
> > >
> > > I'm not sure what is the proper way to solve this. And Ian mentioned
> > > that put code in arch directory could potentially cause other bugs.
> > > So I'm wondering if we could keep this code here for now. I could wor=
k
> > > on it later if we found it's better to be in arch directory.
> >
> > Maybe somewhere in the util/ and keep the main code minimal.
> > IIUC it's only for very recent (or upcoming?) Intel CPUs and we
> > don't have tests (hopefully can run on other arch/CPUs).
> >
> > So I don't think having it here would help fixing potential bugs.
>
> Do you mean by creating a new file in util/ to hold this code?

Yeah, maybe util/intel-tpebs.c (if it's better than arch/x86/...) ?

>
> Yes, this feature is for very recent Intel CPUs. It should only be trigge=
red if
> a metric uses event(s) that has the R modifier in the formula.

Can we have a test with a fake metric so that we can test
the code on non-(or old-)Intel machines?

Thanks,
Namhyung