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Message-ID: <Zv7O_XJZcSIS9I_i@google.com>
Date: Thu, 3 Oct 2024 10:06:05 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Kan Liang <kan.liang@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
linux-perf-users@...r.kernel.org,
Ravi Bangoria <ravi.bangoria@....com>,
Mark Rutland <mark.rutland@....com>,
James Clark <james.clark@....com>, Kajol Jain <kjain@...ux.ibm.com>,
Thomas Richter <tmricht@...ux.ibm.com>,
Atish Patra <atishp@...shpatra.org>,
Palmer Dabbelt <palmer@...osinc.com>,
Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH 7/8] perf tools: Check fallback error and order
On Tue, Oct 01, 2024 at 03:21:50PM -0700, Ian Rogers wrote:
> On Tue, Oct 1, 2024 at 2:36 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > On Tue, Oct 01, 2024 at 11:00:20AM -0700, Ian Rogers wrote:
> > > On Mon, Sep 30, 2024 at 5:20 PM Namhyung Kim <namhyung@...nel.org> wrote:
> > > >
> > > > The perf_event_open might fail due to various reasons, so blindly
> > > > reducing precise_ip level might not be the best way to deal with it.
> > > >
> > > > It seems the kernel return -EOPNOTSUPP when PMU doesn't support the
> > > > given precise level. Let's try again with the correct error code.
> > > >
> > > > This caused a problem on AMD, as it stops on precise_ip of 2 for IBS but
> > > > user events with exclude_kernel=1 cannot make progress. Let's add the
> > > > evsel__handle_error_quirks() to this case specially. I plan to work on
> > > > the kernel side to improve this situation but it'd still need some
> > > > special handling for IBS.
> > > >
> > > > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > > > ---
> > > > tools/perf/util/evsel.c | 27 +++++++++++++++++++++------
> > > > 1 file changed, 21 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > > > index 32e30c293d0c6198..ef8356260eea54cd 100644
> > > > --- a/tools/perf/util/evsel.c
> > > > +++ b/tools/perf/util/evsel.c
> > > > @@ -2419,6 +2419,20 @@ static bool evsel__detect_missing_features(struct evsel *evsel)
> > > > return false;
> > > > }
> > > >
> > > > +static bool evsel__handle_error_quirks(struct evsel *evsel, int error)
> > > > +{
> > > > + /* AMD IBS doesn't support exclude_kernel, forward it to core PMU */
> > >
> > > Should the quirk handling be specific to evsels with the IBS PMU given
> > > the comment above? ie this is a PMU specific workaround rather than an
> > > AMD specific workaround, however, the PMU only exists on AMD :-)
> > >
> > > > + if (error == -EINVAL && evsel->precise_max && evsel->core.attr.precise_ip &&
> > > > + evsel->core.attr.exclude_kernel && x86__is_amd_cpu()) {
> > >
> > > So here rather than x86__is_amd_cpu it would be
> > > !strcmp(evsel->pmu->name, "ibs_...") . But it may be cleaner to move
> > > the logic into pmu.c.
> >
> > I guess the problem is that AMD driver does implicit forwarding to IBS
> > if the legacy hardware events have precise_ip. So it might have just
> > core pmu (or no pmu) in the evsel.
>
> I think the no PMU case should probably have a PMU possibly similar to
> the tool PMU in:
> https://lore.kernel.org/all/20240912190341.919229-1-irogers@google.com/
> But that's not in place yet. You can always use
> perf_pmus__scan_core(NULL) or
> perf_pmus__find_by_type(evsel->core.attr.type or PERF_TYPE_RAW).
> evsel->pmu->is_core && x86__is_amd_cpu() would identify an AMD core
> PMU whereas the code above could fire for IBS or other PMUs.
But IBS is the only PMU on AMD that provides precise_ip IIRC. So I
don't think other events would have it nor have any effect on changing
the value. So maybe we can skip the PMU scanning and just drop to 0?
Thanks,
Namhyung
>
> > >
> > > > + evsel->core.attr.precise_ip = 0;
> > > > + pr_debug2_peo("removing precise_ip on AMD\n");
> > > > + display_attr(&evsel->core.attr);
> > > > + return true;
> > > > + }
> > > > +
> > > > + return false;
> > > > +}
> > > > +
> > > > static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
> > > > struct perf_thread_map *threads,
> > > > int start_cpu_map_idx, int end_cpu_map_idx)
> > > > @@ -2580,9 +2594,6 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
> > > > return 0;
> > > >
> > > > try_fallback:
> > > > - if (evsel__precise_ip_fallback(evsel))
> > > > - goto retry_open;
> > > > -
> > > > if (evsel__ignore_missing_thread(evsel, perf_cpu_map__nr(cpus),
> > > > idx, threads, thread, err)) {
> > > > /* We just removed 1 thread, so lower the upper nthreads limit. */
> > > > @@ -2599,11 +2610,15 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
> > > > if (err == -EMFILE && rlimit__increase_nofile(&set_rlimit))
> > > > goto retry_open;
> > > >
> > > > - if (err != -EINVAL || idx > 0 || thread > 0)
> > > > - goto out_close;
> > > > + if (err == -EOPNOTSUPP && evsel__precise_ip_fallback(evsel))
> > > > + goto retry_open;
> > > >
> > > > - if (evsel__detect_missing_features(evsel))
> > > > + if (err == -EINVAL && evsel__detect_missing_features(evsel))
> > > > goto fallback_missing_features;
> > > > +
> > > > + if (evsel__handle_error_quirks(evsel, err))
> > > > + goto retry_open;
> > > > +
> > > > out_close:
> > > > if (err)
> > > > threads->err_thread = thread;
> > > > --
> > > > 2.46.1.824.gd892dcdcdd-goog
> > > >
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