perf report: Print percentage of each event statistics

It's sometimes useful to see how many samples vs other events in the
data file with percent values.

$ perf report --stat

Aggregated stats:
TOTAL events: 20064
MMAP events: 239 ( 1.2%)
COMM events: 1518 ( 7.6%)
EXIT events: 1 ( 0.0%)
FORK events: 1517 ( 7.6%)
SAMPLE events: 4015 (20.0%)
MMAP2 events: 12769 (63.6%)
FINISHED_ROUND events: 2 ( 0.0%)
THREAD_MAP events: 1 ( 0.0%)
CPU_MAP events: 1 ( 0.0%)
TIME_CONV events: 1 ( 0.0%)
cycles stats:
SAMPLE events: 2475
instructions stats:
SAMPLE events: 1540

Suggested-by: Andi Kleen <[e-mail]>
Reviewed-by: Andi Kleen <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Mark Rutland <[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/ui/stdio/hist.c

···
 {
 	int i;
 	size_t ret = 0;
+	u32 total = stats->nr_events[0];
 
 	for (i = 0; i < PERF_RECORD_HEADER_MAX; ++i) {
 		const char *name;
···
 		if (skip_empty && !stats->nr_events[i])
 			continue;
 
-		ret += fprintf(fp, "%16s events: %10d\n", name, stats->nr_events[i]);
+		if (i && total) {
+			ret += fprintf(fp, "%16s events: %10d  (%4.1f%%)\n",
+				       name, stats->nr_events[i],
+				       100.0 * stats->nr_events[i] / total);
+		} else {
+			ret += fprintf(fp, "%16s events: %10d\n",
+				       name, stats->nr_events[i]);
+		}
 	}
 
 	return ret;