Messages in this thread | | | From | Ian Rogers <> | Date | Wed, 21 Feb 2024 12:19:22 -0800 | Subject | Re: [PATCH v2] perf print-events: make is_event_supported() more robust |
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On Fri, Jan 26, 2024 at 6:56 AM Mark Rutland <mark.rutland@arm.com> 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 >= 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 (but > 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 for > 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 in 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 types > even when these are supported, as they have been since commit: > > 5c816728651ae425 ("arm_pmu: Add PERF_PMU_CAP_EXTENDED_HW_TYPE capability") > > 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 may > 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 priority 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 to > be the same as a PERF_EVENT_TYPE_HARDWARE event (e.g. as is the case for > the M1/M2 PMU's 'cycles' and 'instructions' events). > > Fixes: 82fe2e45cdb00de4 ("perf pmus: Check if we can encode the PMU number 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@armcom/ > > Mark. > > diff --git a/tools/perf/util/print-events.c b/tools/perf/util/print-events.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 = true; > - int open_return; > struct evsel *evsel; > struct perf_event_attr attr = { > .type = type, > @@ -246,20 +245,32 @@ bool is_event_supported(u8 type, u64 config) > > evsel = evsel__new(&attr); > if (evsel) { > - open_return = evsel__open(evsel, NULL, tmap); > - ret = open_return >= 0; > + ret = evsel__open(evsel, NULL, tmap) >= 0; > > - if (open_return == -EACCES) { > + if (!ret) { > /* > - * This happens if the paranoid value > + * The event may fail to open if the paranoid value > * /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 support 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 = 1; > ret = evsel__open(evsel, NULL, tmap) >= 0; > } > + > + if (!ret) { > + /* > + * The event may fail to open if the PMU requires > + * exclude_guest to be set (e.g. as the Apple M1 PMU > + * requires). > + * Re-run with exclude_guest set; we don't do that by > + * default as it's equally legitimate for another PMU > + * driver to require that exclude_guest is clear. > + */ > + evsel->core.attr.exclude_guest = 1; > + ret = evsel__open(evsel, NULL, tmap) >= 0; > + } > + > evsel__delete(evsel); > } > > -- > 2.30.2 >
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