Messages in this thread | | | Date | Fri, 3 Jul 2020 13:00:42 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf evsel: Don't set sample_regs_intr/sample_regs_user for dummy event |
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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 >
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