c4735d9902
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:
/* 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 not be set with
PERF_PMU_CAP_EXTENDED_REGS. But unfortunately now, 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 and attr->sample_regs_user.
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) ]
Committer notes:
Adrian said this when providing his Acked-by:
"
This is fine. It will not break PT.
no_aux_samples is useful for evsels that have been added by the code rather
than requested by the user. For old kernels PT adds sched_switch tracepoint
to track context switches (before the current context switch event was
added) and having auxiliary sample information unnecessarily uses up space
in the perf buffer.
"
Fixes: 0a892c1c9472 ("perf record: Add dummy event during system wide synthesis")
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200720010013.18238-1-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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