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Message-ID: <CAP-5=fURS0OQxHcukS1+NprgyMpAQSr3+BMiYPj5x7=+tcZ8hw@mail.gmail.com>
Date: Wed, 21 Feb 2024 12:19:22 -0800
From: Ian Rogers <irogers@...gle.com>
To: Mark Rutland <mark.rutland@....com>
Cc: linux-kernel@...r.kernel.org, acme@...hat.com, james.clark@....com,
john.g.garry@...cle.com, leo.yan@...aro.org,
linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
marcan@...can.st, maz@...nel.org, mike.leach@...aro.org, namhyung@...nel.org,
suzuki.poulose@....com, tmricht@...ux.ibm.com, will@...nel.org
Subject: Re: [PATCH v2] perf print-events: make is_event_supported() more robust
On Fri, Jan 26, 2024 at 6:56 AM Mark Rutland <mark.rutland@....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@....com>
> Tested-by: Ian Rogers <irogers@...gle.com>
> Tested-by: James Clark <james.clark@....com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Hector Martin <marcan@...can.st>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: James Clark <james.clark@....com>
> Cc: John Garry <john.g.garry@...cle.com>
> Cc: Leo Yan <leo.yan@...aro.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: Thomas Richter <tmricht@...ux.ibm.com>
> Cc: Will Deacon <will@...nel.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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