From: Jiri Olsa <jolsa@redhat.com>
To: Jin Yao <yao.jin@linux.intel.com>
Cc: acme@kernel.org, jolsa@kernel.org, peterz@infradead.org,
mingo@redhat.com, alexander.shishkin@linux.intel.com,
Linux-kernel@vger.kernel.org, ak@linux.intel.com,
kan.liang@intel.com, yao.jin@intel.com, irogers@google.com,
Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH] perf evsel: Don't set sample_regs_intr/sample_regs_user for dummy event
Date: Fri, 3 Jul 2020 13:00:42 +0200 [thread overview]
Message-ID: <20200703110042.GA3282312@krava> (raw)
In-Reply-To: <20200703004215.24418-1-yao.jin@linux.intel.com>
On Fri, Jul 03, 2020 at 08:42:15AM +0800, Jin Yao wrote:
> Since commit 0a892c1c9472 ("perf record: Add dummy event during system wide synthesis"),
> a dummy event is added to capture mmaps.
>
> But if we run perf-record as,
>
> # perf record -e cycles:p -IXMM0 -a -- sleep 1
> Error:
> dummy:HG: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'
>
> The issue is, if we enable the extended regs (-IXMM0), but the
> pmu->capabilities is not set with PERF_PMU_CAP_EXTENDED_REGS, the kernel
> will return -EOPNOTSUPP error.
>
> See following code pieces.
>
> /* in kernel/events/core.c */
> static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
>
> {
> ....
> if (!(pmu->capabilities & PERF_PMU_CAP_EXTENDED_REGS) &&
> has_extended_regs(event))
> ret = -EOPNOTSUPP;
> ....
> }
>
> For software dummy event, the PMU should be not set with
> PERF_PMU_CAP_EXTENDED_REGS. But unfortunately in current code, the dummy
> event has possibility to be set with PERF_REG_EXTENDED_MASK bit.
>
> In evsel__config, /* tools/perf/util/evsel.c */
>
> if (opts->sample_intr_regs) {
> attr->sample_regs_intr = opts->sample_intr_regs;
> }
>
> If we use -IXMM0, the attr>sample_regs_intr will be set with
> PERF_REG_EXTENDED_MASK bit.
>
> It doesn't make sense to set attr->sample_regs_intr for a
> software dummy event.
>
> This patch adds dummy event checking before setting
> attr->sample_regs_intr.
>
> After:
> # ./perf record -e cycles:p -IXMM0 -a -- sleep 1
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.413 MB perf.data (45 samples) ]
LGTM, Adrian (cc-ed) just added another check to the same place,
but it looks like both of them should be there:
https://lore.kernel.org/lkml/20200630133935.11150-2-adrian.hunter@intel.com/
jirka
>
> Fixes: 0a892c1c9472 ("perf record: Add dummy event during system wide synthesis")
> Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
> ---
> tools/perf/util/evsel.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 96e5171dce41..df3315543e86 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1020,12 +1020,12 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
> if (callchain && callchain->enabled && !evsel->no_aux_samples)
> evsel__config_callchain(evsel, opts, callchain);
>
> - if (opts->sample_intr_regs) {
> + if (opts->sample_intr_regs && !is_dummy_event(evsel)) {
> attr->sample_regs_intr = opts->sample_intr_regs;
> evsel__set_sample_bit(evsel, REGS_INTR);
> }
>
> - if (opts->sample_user_regs) {
> + if (opts->sample_user_regs && !is_dummy_event(evsel)) {
> attr->sample_regs_user |= opts->sample_user_regs;
> evsel__set_sample_bit(evsel, REGS_USER);
> }
> --
> 2.17.1
>
next prev parent reply other threads:[~2020-07-03 11:00 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-03 0:42 [PATCH] perf evsel: Don't set sample_regs_intr/sample_regs_user for dummy event Jin Yao
2020-07-03 11:00 ` Jiri Olsa [this message]
2020-07-04 0:31 ` Jin, Yao
2020-07-06 0:47 ` Ian Rogers
2020-07-06 0:55 ` Jin, Yao
2020-07-17 3:33 ` Jin, Yao
2020-07-17 8:24 ` Jiri Olsa
2020-07-17 8:30 ` Jin, Yao
2020-07-17 11:38 ` Arnaldo Carvalho de Melo
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