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 <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-report.c

···
 	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);
···
 	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

···
 	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;