perf stat: Ensure metrics are displayed even with failed events

Currently, `perf stat` skips or hides metrics when the underlying
hardware events cannot be counted (e.g., due to insufficient permissions
or unsupported events).

In `--metric-only` mode, this often results in missing columns or blank
spaces, making the output difficult to parse.

Modify the logic to ensure metrics are consistently displayed by
propagating NAN (Not a Number) through the expression evaluator.
Specifically:

1. Update `prepare_metric()` in stat-shadow.c to treat uncounted events
   (where `run == 0`) as NAN. This leverages the existing math in expr.y
   to propagate NAN through metric expressions.

2. Remove the early return in the display logic's `printout()` function
   that was previously skipping metrics in `--metric-only` mode for
   failed events.
l
3. Simplify `perf_stat__skip_metric_event()` to no longer depend on
   event runtime.

Tested:

1. `perf all metrics test` did not crash while paranoid is 2.

2. Multiple combinations with `CPUs_utilized` while paranoid is 2.

  $ ./perf stat -M CPUs_utilized -a -- sleep 1

   Performance counter stats for 'system wide':

     <not supported> msec cpu-clock:u                      #      nan CPUs  CPUs_utilized
       1,006,356,120      duration_time

         1.004375550 seconds time elapsed

  $ ./perf stat -M CPUs_utilized -a -j -- sleep 1
  {"counter-value" : "<not supported>", "unit" : "msec", "event" : "cpu-clock:u", "event-runtime" : 0, "pcnt-running" : 100.00, "metric-value" : "nan", "metric-unit" : "CPUs  CPUs_utilized"}
  {"counter-value" : "1006642462.000000", "unit" : "", "event" : "duration_time", "event-runtime" : 1, "pcnt-running" : 100.00}

  $ ./perf stat -M CPUs_utilized -a --metric-only -- sleep 1

   Performance counter stats for 'system wide':

    CPUs  CPUs_utilized
                      nan

         1.004424652 seconds time elapsed

  $ ./perf stat -M CPUs_utilized -a --metric-only -j -- sleep 1
  {"CPUs  CPUs_utilized" : "none"}

Reviewed-by: Ian Rogers <[email protected]>
Signed-off-by: Chun-Tse Shao <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Yang Li <[email protected]>
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: Chun-Tse Shao

tools/perf/util/stat-display.c

@@ -820,12 +820,6 @@ static void printout(struct perf_stat_config *config, struct outstate *os,
 	}
 
 	if (run == 0 || ena == 0 || counter->counts->scaled == -1) {
-		if (config->metric_only) {
-			pm(config, os, METRIC_THRESHOLD_UNKNOWN, /*format=*/NULL,
-			   /*unit=*/NULL, /*val=*/0);
-			return;
-		}
-
 		ok = false;
 
 		if (counter->supported) {
@@ -848,33 +842,32 @@ static void printout(struct perf_stat_config *config, struct outstate *os,
 		print_running(config, os, run, ena, /*before_metric=*/true);
 	}
 
-	if (ok) {
-		if (!config->metric_only && counter->default_metricgroup && !counter->default_show_events) {
-			void *from = NULL;
-
-			aggr_printout(config, os, os->evsel, os->id, os->aggr_nr);
-			/* Print out all the metricgroup with the same metric event. */
-			do {
-				int num = 0;
-
-				/* Print out the new line for the next new metricgroup. */
-				if (from) {
-					if (config->json_output)
-						new_line_json(config, (void *)os);
-					else
-						__new_line_std_csv(config, os);
-				}
-
-				print_noise(config, os, counter, noise, /*before_metric=*/true);
-				print_running(config, os, run, ena, /*before_metric=*/true);
-				from = perf_stat__print_shadow_stats_metricgroup(config, counter, aggr_idx,
-										 &num, from, &out);
-			} while (from != NULL);
-		} else {
-			perf_stat__print_shadow_stats(config, counter, aggr_idx, &out);
-		}
+	if (!config->metric_only && counter->default_metricgroup &&
+	    !counter->default_show_events) {
+		void *from = NULL;
+
+		aggr_printout(config, os, os->evsel, os->id, os->aggr_nr);
+		/* Print out all the metricgroup with the same metric event. */
+		do {
+			int num = 0;
+
+			/* Print out the new line for the next new metricgroup. */
+			if (from) {
+				if (config->json_output)
+					new_line_json(config, (void *)os);
+				else
+					__new_line_std_csv(config, os);
+			}
+
+			print_noise(config, os, counter, noise,
+				    /*before_metric=*/true);
+			print_running(config, os, run, ena,
+				      /*before_metric=*/true);
+			from = perf_stat__print_shadow_stats_metricgroup(
+				config, counter, aggr_idx, &num, from, &out);
+		} while (from != NULL);
 	} else {
-		pm(config, os, METRIC_THRESHOLD_UNKNOWN, /*format=*/NULL, /*unit=*/NULL, /*val=*/0);
+		perf_stat__print_shadow_stats(config, counter, aggr_idx, &out);
 	}
 
 	if (!config->metric_only) {
@@ -987,7 +980,7 @@ static void print_counter_aggrdata(struct perf_stat_config *config,
 	ena = aggr->counts.ena;
 	run = aggr->counts.run;
 
-	if (perf_stat__skip_metric_event(counter, ena, run))
+	if (perf_stat__skip_metric_event(counter))
 		return;
 
 	if (val == 0 && should_skip_zero_counter(config, counter, &id))

tools/perf/util/stat-shadow.c

@@ -83,7 +83,7 @@ static int prepare_metric(struct perf_stat_config *config,
 		}
 		/* Time events are always on CPU0, the first aggregation index. */
 		aggr = &ps->aggr[is_tool_time ? tool_aggr_idx : aggr_idx];
-		if (!aggr || !metric_events[i]->supported) {
+		if (!aggr || !metric_events[i]->supported || aggr->counts.run == 0) {
 			/*
 			 * Not supported events will have a count of 0, which
 			 * can be confusing in a metric. Explicitly set the
@@ -335,14 +335,10 @@ void perf_stat__print_shadow_stats(struct perf_stat_config *config,
  * perf_stat__skip_metric_event - Skip the evsel in the Default metricgroup,
  *				  if it's not running or not the metric event.
  */
-bool perf_stat__skip_metric_event(struct evsel *evsel,
-				  u64 ena, u64 run)
+bool perf_stat__skip_metric_event(struct evsel *evsel)
 {
 	if (!evsel->default_metricgroup)
 		return false;
 
-	if (!ena || !run)
-		return true;
-
 	return !metricgroup__lookup(&evsel->evlist->metric_events, evsel, false);
 }

tools/perf/util/stat.h

@@ -163,7 +163,7 @@ void perf_stat__print_shadow_stats(struct perf_stat_config *config,
 				   struct evsel *evsel,
 				   int aggr_idx,
 				   struct perf_stat_output_ctx *out);
-bool perf_stat__skip_metric_event(struct evsel *evsel, u64 ena, u64 run);
+bool perf_stat__skip_metric_event(struct evsel *evsel);
 void *perf_stat__print_shadow_stats_metricgroup(struct perf_stat_config *config,
 						struct evsel *evsel,
 						int aggr_idx,