perf report: Fix the output for stdio events list

Changing the output header for reporting forced groups via --groups
option on non grouped events, like:

  $ perf record -e 'cycles,instructions'
  $ perf report --stdio --group

Before:

  # Samples: 24  of event 'anon group { cycles:u, instructions:u }'

After:

  # Samples: 24  of events 'cycles:u, instructions:u'

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Fixes: ad52b8c ("perf report: Add support to display group output for non group events")
Link: http://lkml.kernel.org/r/20180307155020.32613-2-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-report.c

@@ -400,8 +400,10 @@ static size_t hists__fprintf_nr_sample_events(struct hists *hists, struct report
 
 	nr_samples = convert_unit(nr_samples, &unit);
 	ret = fprintf(fp, "# Samples: %lu%c", nr_samples, unit);
-	if (evname != NULL)
-		ret += fprintf(fp, " of event '%s'", evname);
+	if (evname != NULL) {
+		ret += fprintf(fp, " of event%s '%s'",
+			       evsel->nr_members > 1 ? "s" : "", evname);
+	}
 
 	if (rep->time_str)
 		ret += fprintf(fp, " (time slices: %s)", rep->time_str);
@@ -1175,8 +1177,17 @@ int cmd_report(int argc, const char **argv)
 	has_br_stack = perf_header__has_feat(&session->header,
 					     HEADER_BRANCH_STACK);
 
-	if (group_set && !session->evlist->nr_groups)
+	/*
+	 * Events in data file are not collect in groups, but we still want
+	 * the group display. Set the artificial group and set the leader's
+	 * forced_leader flag to notify the display code.
+	 */
+	if (group_set && !session->evlist->nr_groups) {
+		struct perf_evsel *leader = perf_evlist__first(session->evlist);
+
 		perf_evlist__set_leader(session->evlist);
+		leader->forced_leader = true;
+	}
 
 	if (itrace_synth_opts.last_branch)
 		has_br_stack = true;

tools/perf/ui/browsers/hists.c

@@ -2261,8 +2261,9 @@ static int perf_evsel_browser_title(struct hist_browser *browser,
 
 	nr_samples = convert_unit(nr_samples, &unit);
 	printed = scnprintf(bf, size,
-			   "Samples: %lu%c of event '%s',%s%sEvent count (approx.): %" PRIu64,
-			   nr_samples, unit, ev_name, sample_freq_str, enable_ref ? ref : " ", nr_events);
+			   "Samples: %lu%c of event%s '%s',%s%sEvent count (approx.): %" PRIu64,
+			   nr_samples, unit, evsel->nr_members > 1 ? "s" : "",
+			   ev_name, sample_freq_str, enable_ref ? ref : " ", nr_events);
 
 
 	if (hists->uid_filter_str)

tools/perf/util/evsel.c

@@ -622,22 +622,34 @@ const char *perf_evsel__group_name(struct perf_evsel *evsel)
 	return evsel->group_name ?: "anon group";
 }
 
+/*
+ * Returns the group details for the specified leader,
+ * with following rules.
+ *
+ *  For record -e '{cycles,instructions}'
+ *    'anon group { cycles:u, instructions:u }'
+ *
+ *  For record -e 'cycles,instructions' and report --group
+ *    'cycles:u, instructions:u'
+ */
 int perf_evsel__group_desc(struct perf_evsel *evsel, char *buf, size_t size)
 {
-	int ret;
+	int ret = 0;
 	struct perf_evsel *pos;
 	const char *group_name = perf_evsel__group_name(evsel);
 
-	ret = scnprintf(buf, size, "%s", group_name);
+	if (!evsel->forced_leader)
+		ret = scnprintf(buf, size, "%s { ", group_name);
 
-	ret += scnprintf(buf + ret, size - ret, " { %s",
+	ret += scnprintf(buf + ret, size - ret, "%s",
 			 perf_evsel__name(evsel));
 
 	for_each_group_member(pos, evsel)
 		ret += scnprintf(buf + ret, size - ret, ", %s",
 				 perf_evsel__name(pos));
 
-	ret += scnprintf(buf + ret, size - ret, " }");
+	if (!evsel->forced_leader)
+		ret += scnprintf(buf + ret, size - ret, " }");
 
 	return ret;
 }

tools/perf/util/evsel.h

@@ -125,6 +125,7 @@ struct perf_evsel {
 	bool			per_pkg;
 	bool			precise_max;
 	bool			ignore_missing_thread;
+	bool			forced_leader;
 	/* parse modifier helper */
 	int			exclude_GH;
 	int			nr_members;