perf stat: Fix summary output in CSV with --metric-only

It should not print "summary" for each event when --metric-only is set.

Before:

  $ sudo perf stat -a --per-socket --summary -x, --metric-only true
   time,socket,cpusGhz,insn per cycle,branch-misses of all branches,
       0.000709079,S0,8,0.893,2.40,0.45,
  S0,8,         summary,         summary,         summary,         summary,         summary,0.893,         summary,2.40,         summary,         summary,0.45,

After:

  $ sudo perf stat -a --per-socket --summary -x, --metric-only true
   time,socket,cpusGHz,insn per cycle,branch-misses of all branches,
       0.000882297,S0,8,0.598,1.64,0.64,
           summary,S0,8,0.598,1.64,0.64,
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20221112032244.1077370-11-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/stat-display.c

@@ -549,7 +549,7 @@ static void printout(struct perf_stat_config *config, struct aggr_cpu_id id, int
 	}
 
 	if (!config->no_csv_summary && config->csv_output &&
-	    config->summary && !config->interval) {
+	    config->summary && !config->interval && !config->metric_only) {
 		fprintf(config->output, "%16s%s", "summary", config->csv_sep);
 	}
 
@@ -732,8 +732,13 @@ static void print_aggr(struct perf_stat_config *config,
 	 * Without each counter has its own line.
 	 */
 	for (s = 0; s < config->aggr_map->nr; s++) {
-		if (prefix && metric_only)
-			fprintf(output, "%s", prefix);
+		if (metric_only) {
+			if (prefix)
+				fprintf(output, "%s", prefix);
+			else if (config->summary && !config->no_csv_summary &&
+				 config->csv_output && !config->interval)
+				fprintf(output, "%16s%s", "summary", config->csv_sep);
+		}
 
 		first = true;
 		evlist__for_each_entry(evlist, counter) {