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Date: Wed, 15 May 2024 17:14:28 +0000
From: "Wang, Weilin" <weilin.wang@...el.com>
To: Ian Rogers <irogers@...gle.com>
CC: Namhyung Kim <namhyung@...nel.org>, 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>, "Hunter, Adrian" <adrian.hunter@...el.com>,
"Kan Liang" <kan.liang@...ux.intel.com>, "linux-perf-users@...r.kernel.org"
<linux-perf-users@...r.kernel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "Taylor, Perry" <perry.taylor@...el.com>,
"Alt, Samantha" <samantha.alt@...el.com>, "Biggers, Caleb"
<caleb.biggers@...el.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.
> -----Original Message-----
> From: Ian Rogers <irogers@...gle.com>
> Sent: Tuesday, May 14, 2024 11:07 PM
> To: Wang, Weilin <weilin.wang@...el.com>
> Cc: Namhyung Kim <namhyung@...nel.org>; 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>; Hunter,
> Adrian <adrian.hunter@...el.com>; Kan Liang <kan.liang@...ux.intel.com>;
> linux-perf-users@...r.kernel.org; linux-kernel@...r.kernel.org; Taylor, Perry
> <perry.taylor@...el.com>; Alt, Samantha <samantha.alt@...el.com>; Biggers,
> Caleb <caleb.biggers@...el.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.
>
> On Tue, May 14, 2024 at 10:57 PM Wang, Weilin <weilin.wang@...el.com>
> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Namhyung Kim <namhyung@...nel.org>
> > > Sent: Wednesday, April 24, 2024 11:50 AM
> > > To: Wang, Weilin <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>; Hunter,
> > > Adrian <adrian.hunter@...el.com>; Kan Liang <kan.liang@...ux.intel.com>;
> > > linux-perf-users@...r.kernel.org; linux-kernel@...r.kernel.org; Taylor,
> Perry
> > > <perry.taylor@...el.com>; Alt, Samantha <samantha.alt@...el.com>;
> Biggers,
> > > Caleb <caleb.biggers@...el.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.
> > >
> > > On Wed, Apr 24, 2024 at 10:08 AM Wang, Weilin
> <weilin.wang@...el.com>
> > > wrote:
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Namhyung Kim <namhyung@...nel.org>
> > > > > Sent: Tuesday, April 23, 2024 4:06 PM
> > > > > To: Wang, Weilin <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>;
> Hunter,
> > > > > Adrian <adrian.hunter@...el.com>; Kan Liang
> <kan.liang@...ux.intel.com>;
> > > > > linux-perf-users@...r.kernel.org; linux-kernel@...r.kernel.org; Taylor,
> > > Perry
> > > > > <perry.taylor@...el.com>; Alt, Samantha <samantha.alt@...el.com>;
> > > Biggers,
> > > > > Caleb <caleb.biggers@...el.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.
> > > > >
> > > > > On Tue, Apr 23, 2024 at 3:16 PM Wang, Weilin
> <weilin.wang@...el.com>
> > > > > wrote:
> > > > > > > > > > -static int __run_perf_record(void)
> > > > > > > > > > +static int __run_perf_record(const char **record_argv)
> > > > > > > > > > {
> > > > > > > > > > + int i = 0;
> > > > > > > > > > + struct tpebs_event *e;
> > > > > > > > > > +
> > > > > > > > > > pr_debug("Prepare perf record for retire_latency\n");
> > > > > > > > > > +
> > > > > > > > > > + record_argv[i++] = "perf";
> > > > > > > > > > + record_argv[i++] = "record";
> > > > > > > > > > + record_argv[i++] = "-W";
> > > > > > > > > > + record_argv[i++] = "--synth=no";
> > > > > > > > > > +
> > > > > > > > > > + if (stat_config.user_requested_cpu_list) {
> > > > > > > > > > + record_argv[i++] = "-C";
> > > > > > > > > > + record_argv[i++] =
> stat_config.user_requested_cpu_list;
> > > > > > > > > > + }
> > > > > > > > > > +
> > > > > > > > > > + if (stat_config.system_wide)
> > > > > > > > > > + record_argv[i++] = "-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++] = "-e";
> > > > > > > > > > + record_argv[i++] = e->name;
> > > > > > > > > > + }
> > > > > > > > > > +
> > > > > > > > > > + record_argv[i++] = "-o";
> > > > > > > > > > + record_argv[i++] = 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
> > > work
> > > > > > > > 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
> triggered 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?
> > > >
> > > > All the existing metrics in non-(or old-)Intel CPUs should work as usual.
> So I
> > > think
> > > > existing metric tests should work for it.
> > > >
> > > > If we want to add a fake metric uses the :R modifier for those platforms,
> the
> > > metric
> > > > should either fail (if the fake metric uses an event not exist on the test
> > > platform) or
> > > > return all 0 retire latency data.
> > > >
> > > > So, I'm not quite sure what we want the fake metric to test for. Maybe we
> > > could
> > > > continue using existing metric tests to ensure all the defined metrics work
> > > correctly
> > > > in each machine under test?
> > >
> > > I think it's ok to return all 0 retire latency for fake tPEBS metrics.
> > > It's just to verify the background record + report logic works ok.
> >
> > Hi Namhyung,
> >
> > After think more about how TPEBS and metrics work, I feel should discuss
> more
> > about defining a fake TPEBS metric in unsupported platforms.
> > If we'd like a add fake metrics, where should we define and store these
> metrics?
> > Should we add this type of metrics for every platform? All the official metrics
> > we publish are defined by architect and stored in JSON files under separate
> > directories for each platform. I think it is not a good idea to place fake metrics
> > together with real metrics. Could you please let me know if there is any other
> > method to define fake metrics for testing?
>
> We do put fake events/metrics in the "test" arch:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-
> next.git/tree/tools/perf/pmu-events/arch/test/test_soc/cpu/metrics.json
>
> It is something of a pain bringing things here over to the
> NO_JEVENTS=1 (ie no python) empty-pmu-events.c file. I agree on not
> wanting to pollute real metrics with test metrics, we currently just
> use the test metrics to fake up some expression parsing tests:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-
> next.git/tree/tools/perf/tests/pmu-events.c#n811
>
Thanks Ian! I will work on this.
Best,
Weilin
> Thanks,
> Ian
>
> > Thanks,
> > Weilin
> >
> > >
> > > Thanks,
> > > Namhyung
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