perf report: Show per-event LOST SAMPLES stat

Display lost samples with --stat (if not zero):

  $ perf report --stat
    Aggregated stats:
             TOTAL events:         64
              COMM events:          2  ( 3.1%)
              EXIT events:          1  ( 1.6%)
            SAMPLE events:         26  (40.6%)
             MMAP2 events:          4  ( 6.2%)
      LOST_SAMPLES events:          1  ( 1.6%)
              ATTR events:          2  ( 3.1%)
    FINISHED_ROUND events:          1  ( 1.6%)
          ID_INDEX events:          1  ( 1.6%)
        THREAD_MAP events:          1  ( 1.6%)
           CPU_MAP events:          1  ( 1.6%)
      EVENT_UPDATE events:          2  ( 3.1%)
         TIME_CONV events:          1  ( 1.6%)
           FEATURE events:         20  (31.2%)
     FINISHED_INIT events:          1  ( 1.6%)
  cycles:uH stats:
            SAMPLE events:         14
      LOST_SAMPLES events:          1
  instructions:uH stats:
            SAMPLE events:         12

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220901195739.668604-6-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-report.c

@@ -752,6 +752,22 @@ static int count_sample_event(struct perf_tool *tool __maybe_unused,
 	return 0;
 }
 
+static int count_lost_samples_event(struct perf_tool *tool,
+				    union perf_event *event,
+				    struct perf_sample *sample,
+				    struct machine *machine __maybe_unused)
+{
+	struct report *rep = container_of(tool, struct report, tool);
+	struct evsel *evsel;
+
+	evsel = evlist__id2evsel(rep->session->evlist, sample->id);
+	if (evsel) {
+		hists__inc_nr_lost_samples(evsel__hists(evsel),
+					   event->lost_samples.lost);
+	}
+	return 0;
+}
+
 static int process_attr(struct perf_tool *tool __maybe_unused,
 			union perf_event *event,
 			struct evlist **pevlist);
@@ -761,6 +777,7 @@ static void stats_setup(struct report *rep)
 	memset(&rep->tool, 0, sizeof(rep->tool));
 	rep->tool.attr = process_attr;
 	rep->tool.sample = count_sample_event;
+	rep->tool.lost_samples = count_lost_samples_event;
 	rep->tool.no_warn = true;
 }
 

tools/perf/util/hist.c

@@ -2683,12 +2683,16 @@ size_t evlist__fprintf_nr_events(struct evlist *evlist, FILE *fp,
 	evlist__for_each_entry(evlist, pos) {
 		struct hists *hists = evsel__hists(pos);
 
-		if (skip_empty && !hists->stats.nr_samples)
+		if (skip_empty && !hists->stats.nr_samples && !hists->stats.nr_lost_samples)
 			continue;
 
 		ret += fprintf(fp, "%s stats:\n", evsel__name(pos));
-		ret += fprintf(fp, "%16s events: %10d\n",
-			       "SAMPLE", hists->stats.nr_samples);
+		if (hists->stats.nr_samples)
+			ret += fprintf(fp, "%16s events: %10d\n",
+				       "SAMPLE", hists->stats.nr_samples);
+		if (hists->stats.nr_lost_samples)
+			ret += fprintf(fp, "%16s events: %10d\n",
+				       "LOST_SAMPLES", hists->stats.nr_lost_samples);
 	}
 
 	return ret;