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From: Namhyung Kim <namhyung@kernel.org>
Date: Thu, 22 Feb 2024 09:02:04 -0800
Message-ID: <CAM9d7cj=tN8ACGFMmkdL_RE5R-4SCd8Zg3trJ15TvOJKpcXABQ@mail.gmail.com>
Subject: Re: [PATCH v2] perf print-events: make is_event_supported() more robust
To: marcan@marcan.st, maz@kernel.org
Cc: Ian Rogers <irogers@google.com>, Mark Rutland <mark.rutland@arm.com>, 
	linux-kernel@vger.kernel.org, acme@redhat.com, james.clark@arm.com, 
	john.g.garry@oracle.com, leo.yan@linaro.org, 
	linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, 
	mike.leach@linaro.org, suzuki.poulose@arm.com, tmricht@linux.ibm.com, 
	will@kernel.org
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Hector and Marc, can you please take a look?

Thanks,
Namhyung


On Wed, Feb 21, 2024 at 12:19=E2=80=AFPM Ian Rogers <irogers@google.com> wr=
ote:
>
> On Fri, Jan 26, 2024 at 6:56=E2=80=AFAM Mark Rutland <mark.rutland@arm.co=
m> wrote:
> >
> > Currently the perf tool doesn't detect support for extended event types
> > on Apple M1/M2 systems, and will not auto-expand plain PERF_EVENT_TYPE
> > hardware events into per-PMU events. This is due to the detection of
> > extended event types not handling mandatory filters required by the
> > M1/M2 PMU driver.
> >
> > PMU drivers and the core perf_events code can require that
> > perf_event_attr::exclude_* filters are configured in a specific way and
> > may reject certain configurations of filters, for example:
> >
> > (a) Many PMUs lack support for any event filtering, and require all
> >     perf_event_attr::exclude_* bits to be clear. This includes Alpha's
> >     CPU PMU, and ARM CPU PMUs prior to the introduction of PMUv2 in
> >     ARMv7,
> >
> > (b) When /proc/sys/kernel/perf_event_paranoid >=3D 2, the perf core
> >     requires that perf_event_attr::exclude_kernel is set.
> >
> > (c) The Apple M1/M2 PMU requires that perf_event_attr::exclude_guest is
> >     set as the hardware PMU does not count while a guest is running (bu=
t
> >     might be extended in future to do so).
> >
> > In is_event_supported(), we try to account for cases (a) and (b), first
> > attempting to open an event without any filters, and if this fails,
> > retrying with perf_event_attr::exclude_kernel set. We do not account fo=
r
> > case (c), or any other filters that drivers could theoretically require
> > to be set.
> >
> > Thus is_event_supported() will fail to detect support for any events
> > targeting an Apple M1/M2 PMU, even where events would be supported with
> > perf_event_attr:::exclude_guest set.
> >
> > Since commit:
> >
> >   82fe2e45cdb00de4 ("perf pmus: Check if we can encode the PMU number i=
n perf_event_attr.type")
> >
> > ... we use is_event_supported() to detect support for extended types,
> > with the PMU ID encoded into the perf_event_attr::type. As above, on an
> > Apple M1/M2 system this will always fail to detect that the event is
> > supported, and consequently we fail to detect support for extended type=
s
> > even when these are supported, as they have been since commit:
> >
> >   5c816728651ae425 ("arm_pmu: Add PERF_PMU_CAP_EXTENDED_HW_TYPE capabil=
ity")
> >
> > Due to this, the perf tool will not automatically expand plain
> > PERF_TYPE_HARDWARE events into per-PMU events, even when all the
> > necessary kernel support is present.
> >
> > This patch updates is_event_supported() to additionally try opening
> > events with perf_event_attr::exclude_guest set, allowing support for
> > events to be detected on Apple M1/M2 systems. I believe that this is
> > sufficient for all contemporary CPU PMU drivers, though in future it ma=
y
> > be necessary to check for other combinations of filter bits.
> >
> > I've deliberately changed the check to not expect a specific error code
> > for missing filters, as today ;the kernel may return a number of
> > different error codes for missing filters (e.g. -EACCESS, -EINVAL, or
> > -EOPNOTSUPP) depending on why and where the filter configuration is
> > rejected, and retrying for any error is more robust.
> >
> > Note that this does not remove the need for commit:
> >
> >   a24d9d9dc096fc0d ("perf parse-events: Make legacy events lower priori=
ty than sysfs/JSON")
> >
> > ... which is still necessary so that named-pmu/event/ events work on
> > kernels without extended type support, even if the event name happens t=
o
> > be the same as a PERF_EVENT_TYPE_HARDWARE event (e.g. as is the case fo=
r
> > the M1/M2 PMU's 'cycles' and 'instructions' events).
> >
> > Fixes: 82fe2e45cdb00de4 ("perf pmus: Check if we can encode the PMU num=
ber in perf_event_attr.type")
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Tested-by: Ian Rogers <irogers@google.com>
> > Tested-by: James Clark <james.clark@arm.com>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Cc: Hector Martin <marcan@marcan.st>
> > Cc: Ian Rogers <irogers@google.com>
> > Cc: James Clark <james.clark@arm.com>
> > Cc: John Garry <john.g.garry@oracle.com>
> > Cc: Leo Yan <leo.yan@linaro.org>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Mike Leach <mike.leach@linaro.org>
> > Cc: Namhyung Kim <namhyung@kernel.org>
> > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Cc: Thomas Richter <tmricht@linux.ibm.com>
> > Cc: Will Deacon <will@kernel.org>
>
> Ping. Could we land this one?
>
> Thanks,
> Ian
>
> > ---
> >  tools/perf/util/print-events.c | 27 +++++++++++++++++++--------
> >  1 file changed, 19 insertions(+), 8 deletions(-)
> >
> > Since v1 [1]:
> > * Fix typos in commit message
> > * Accumulate tags
> >
> > [1] https://lore.kernel.org/lkml/20240116170348.463479-1-mark.rutland@a=
rm.com/
> >
> > Mark.
> >
> > diff --git a/tools/perf/util/print-events.c b/tools/perf/util/print-eve=
nts.c
> > index b0fc48be623f3..4f67e8f00a4d6 100644
> > --- a/tools/perf/util/print-events.c
> > +++ b/tools/perf/util/print-events.c
> > @@ -232,7 +232,6 @@ void print_sdt_events(const struct print_callbacks =
*print_cb, void *print_state)
> >  bool is_event_supported(u8 type, u64 config)
> >  {
> >         bool ret =3D true;
> > -       int open_return;
> >         struct evsel *evsel;
> >         struct perf_event_attr attr =3D {
> >                 .type =3D type,
> > @@ -246,20 +245,32 @@ bool is_event_supported(u8 type, u64 config)
> >
> >         evsel =3D evsel__new(&attr);
> >         if (evsel) {
> > -               open_return =3D evsel__open(evsel, NULL, tmap);
> > -               ret =3D open_return >=3D 0;
> > +               ret =3D evsel__open(evsel, NULL, tmap) >=3D 0;
> >
> > -               if (open_return =3D=3D -EACCES) {
> > +               if (!ret) {
> >                         /*
> > -                        * This happens if the paranoid value
> > +                        * The event may fail to open if the paranoid v=
alue
> >                          * /proc/sys/kernel/perf_event_paranoid is set =
to 2
> > -                        * Re-run with exclude_kernel set; we don't do =
that
> > -                        * by default as some ARM machines do not suppo=
rt it.
> > -                        *
> > +                        * Re-run with exclude_kernel set; we don't do =
that by
> > +                        * default as some ARM machines do not support =
it.
> >                          */
> >                         evsel->core.attr.exclude_kernel =3D 1;
> >                         ret =3D evsel__open(evsel, NULL, tmap) >=3D 0;
> >                 }
> > +
> > +               if (!ret) {
> > +                       /*
> > +                        * The event may fail to open if the PMU requir=
es
> > +                        * exclude_guest to be set (e.g. as the Apple M=
1 PMU
> > +                        * requires).
> > +                        * Re-run with exclude_guest set; we don't do t=
hat by
> > +                        * default as it's equally legitimate for anoth=
er PMU
> > +                        * driver to require that exclude_guest is clea=
r.
> > +                        */
> > +                       evsel->core.attr.exclude_guest =3D 1;
> > +                       ret =3D evsel__open(evsel, NULL, tmap) >=3D 0;
> > +               }
> > +
> >                 evsel__delete(evsel);
> >         }
> >
> > --
> > 2.30.2
> >