perf report: Add --skip-empty option to suppress 0 event stat

To make the output more readable, I think it's better to remove 0's in
the output.  Also the dummy event has no event stats so it just wasts
the space.  Let's use the --skip-empty option to suppress it.

  $ perf report --stat --skip-empty

  Aggregated stats:
             TOTAL events:      16530
              MMAP events:        226
              COMM events:       1596
              EXIT events:          2
          THROTTLE events:        121
        UNTHROTTLE events:        117
              FORK events:       1595
            SAMPLE events:        719
             MMAP2 events:      12147
            CGROUP events:          2
    FINISHED_ROUND events:          2
        THREAD_MAP events:          1
           CPU_MAP events:          1
         TIME_CONV events:          1
  cycles stats:
            SAMPLE events:        719

Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210427013717.1651674-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-report.txt

@@ -571,6 +571,9 @@ include::itrace.txt[]
 			    sampled cycles
 	'Avg Cycles'      - block average sampled cycles
 
+--skip-empty::
+	Do not print 0 results in the --stat output.
+
 include::callchain-overhead-calculation.txt[]
 
 SEE ALSO

tools/perf/builtin-annotate.c

@@ -404,8 +404,8 @@ static int __cmd_annotate(struct perf_annotate *ann)
 		goto out;
 
 	if (dump_trace) {
-		perf_session__fprintf_nr_events(session, stdout);
+		perf_session__fprintf_nr_events(session, stdout, false);
-		evlist__fprintf_nr_events(session->evlist, stdout);
+		evlist__fprintf_nr_events(session->evlist, stdout, false);
 		goto out;
 	}
 

tools/perf/builtin-report.c

@@ -85,6 +85,7 @@ struct report {
 	bool			group_set;
 	bool			stitch_lbr;
 	bool			disable_order;
+	bool			skip_empty;
 	int			max_stack;
 	struct perf_read_values	show_threads_values;
 	struct annotation_options annotation_opts;
@@ -530,6 +531,9 @@ static int evlist__tty_browse_hists(struct evlist *evlist, struct report *rep, c
 		if (symbol_conf.event_group && !evsel__is_group_leader(pos))
 			continue;
 
+		if (rep->skip_empty && !hists->stats.nr_samples)
+			continue;
+
 		hists__fprintf_nr_sample_events(hists, rep, evname, stdout);
 
 		if (rep->total_cycles_mode) {
@@ -731,8 +735,8 @@ static int stats_print(struct report *rep)
 {
 	struct perf_session *session = rep->session;
 
-	perf_session__fprintf_nr_events(session, stdout);
+	perf_session__fprintf_nr_events(session, stdout, rep->skip_empty);
-	perf_evlist__fprintf_nr_events(session->evlist, stdout);
+	evlist__fprintf_nr_events(session->evlist, stdout, rep->skip_empty);
 	return 0;
 }
 
@@ -944,8 +948,10 @@ static int __cmd_report(struct report *rep)
 			perf_session__fprintf_dsos(session, stdout);
 
 		if (dump_trace) {
-			perf_session__fprintf_nr_events(session, stdout);
+			perf_session__fprintf_nr_events(session, stdout,
-			evlist__fprintf_nr_events(session->evlist, stdout);
+							rep->skip_empty);
+			evlist__fprintf_nr_events(session->evlist, stdout,
+						  rep->skip_empty);
 			return 0;
 		}
 	}
@@ -1313,6 +1319,8 @@ int cmd_report(int argc, const char **argv)
 		    "Sort all blocks by 'Sampled Cycles%'"),
 	OPT_BOOLEAN(0, "disable-order", &report.disable_order,
 		    "Disable raw trace ordering"),
+	OPT_BOOLEAN(0, "skip-empty", &report.skip_empty,
+		    "Do not display empty (or dummy) events in the output"),
 	OPT_END()
 	};
 	struct perf_data data = {

tools/perf/ui/stdio/hist.c

@@ -897,7 +897,8 @@ out:
 	return ret;
 }
 
-size_t events_stats__fprintf(struct events_stats *stats, FILE *fp)
+size_t events_stats__fprintf(struct events_stats *stats, FILE *fp,
+			     bool skip_empty)
 {
 	int i;
 	size_t ret = 0;
@@ -908,6 +909,8 @@ size_t events_stats__fprintf(struct events_stats *stats, FILE *fp)
 		name = perf_event__name(i);
 		if (!strcmp(name, "UNKNOWN"))
 			continue;
+		if (skip_empty && !stats->nr_events[i])
+			continue;
 
 		ret += fprintf(fp, "%16s events: %10d\n", name, stats->nr_events[i]);
 	}

tools/perf/util/events_stats.h

@@ -50,6 +50,7 @@ struct hists_stats {
 
 void events_stats__inc(struct events_stats *stats, u32 type);
 
-size_t events_stats__fprintf(struct events_stats *stats, FILE *fp);
+size_t events_stats__fprintf(struct events_stats *stats, FILE *fp,
+			     bool skip_empty);
 
 #endif /* __PERF_EVENTS_STATS_ */

tools/perf/util/hist.c

@@ -2676,7 +2676,8 @@ void hist__account_cycles(struct branch_stack *bs, struct addr_location *al,
 	}
 }
 
-size_t evlist__fprintf_nr_events(struct evlist *evlist, FILE *fp)
+size_t evlist__fprintf_nr_events(struct evlist *evlist, FILE *fp,
+				 bool skip_empty)
 {
 	struct evsel *pos;
 	size_t ret = 0;
@@ -2684,6 +2685,9 @@ 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)
+			continue;
+
 		ret += fprintf(fp, "%s stats:\n", evsel__name(pos));
 		ret += fprintf(fp, "%16s events: %10d\n",
 			       "SAMPLE", hists->stats.nr_samples);

tools/perf/util/hist.h

@@ -202,7 +202,8 @@ void hists__inc_nr_samples(struct hists *hists, bool filtered);
 size_t hists__fprintf(struct hists *hists, bool show_header, int max_rows,
 		      int max_cols, float min_pcnt, FILE *fp,
 		      bool ignore_callchains);
-size_t evlist__fprintf_nr_events(struct evlist *evlist, FILE *fp);
+size_t evlist__fprintf_nr_events(struct evlist *evlist, FILE *fp,
+				 bool skip_empty);
 
 void hists__filter_by_dso(struct hists *hists);
 void hists__filter_by_thread(struct hists *hists);

tools/perf/util/session.c

@@ -2352,7 +2352,8 @@ size_t perf_session__fprintf_dsos_buildid(struct perf_session *session, FILE *fp
 	return machines__fprintf_dsos_buildid(&session->machines, fp, skip, parm);
 }
 
-size_t perf_session__fprintf_nr_events(struct perf_session *session, FILE *fp)
+size_t perf_session__fprintf_nr_events(struct perf_session *session, FILE *fp,
+				       bool skip_empty)
 {
 	size_t ret;
 	const char *msg = "";
@@ -2362,7 +2363,7 @@ size_t perf_session__fprintf_nr_events(struct perf_session *session, FILE *fp)
 
 	ret = fprintf(fp, "\nAggregated stats:%s\n", msg);
 
-	ret += events_stats__fprintf(&session->evlist->stats, fp);
+	ret += events_stats__fprintf(&session->evlist->stats, fp, skip_empty);
 	return ret;
 }
 

tools/perf/util/session.h

@@ -113,7 +113,8 @@ size_t perf_session__fprintf_dsos(struct perf_session *session, FILE *fp);
 size_t perf_session__fprintf_dsos_buildid(struct perf_session *session, FILE *fp,
 					  bool (fn)(struct dso *dso, int parm), int parm);
 
-size_t perf_session__fprintf_nr_events(struct perf_session *session, FILE *fp);
+size_t perf_session__fprintf_nr_events(struct perf_session *session, FILE *fp,
+				       bool skip_empty);
 
 struct evsel *perf_session__find_first_evtype(struct perf_session *session,
 					    unsigned int type);