perf evsel: Don't set sample_regs_intr/sample_regs_user for dummy event

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>

1 files changed, 4 insertions, 2 deletions

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 9aa51a65593d..11794d3b7879 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1014,12 +1014,14 @@ 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 && !evsel->no_aux_samples) {
+	if (opts->sample_intr_regs && !evsel->no_aux_samples &&
+	    !evsel__is_dummy_event(evsel)) {
 		attr->sample_regs_intr = opts->sample_intr_regs;
 		evsel__set_sample_bit(evsel, REGS_INTR);
 	}
 
-	if (opts->sample_user_regs && !evsel->no_aux_samples) {
+	if (opts->sample_user_regs && !evsel->no_aux_samples &&
+	    !evsel__is_dummy_event(evsel)) {
 		attr->sample_regs_user |= opts->sample_user_regs;
 		evsel__set_sample_bit(evsel, REGS_USER);
 	}