[PATCH] perf stat: Fix false NMI watchdog warning in aggregation modes

[Chun-Tse Shao]

In aggregation modes (e.g. --per-socket, --per-die, etc.), a
counter might not be scheduled or counted on specific aggregate
groups if it was not assigned to the CPUs belonging to those
groups. However, the printout() check triggers the
"print_free_counters_hint" logic unconditionally for any
supported counter with a missing count. This results in a false
"Some events weren't counted. Try disabling the NMI watchdog"
warning.

This warning was originally introduced in commit 02d492e5dcb7
("perf stat: Issue a HW watchdog disable hint").

To fix this, add the helper evsel__should_run_on_aggr() to
verify if the counter was supposed to run on the aggregate CPU
ID before triggering the hint. Additionally, correctly handle
per-thread/per-process execution (which uses a dummy CPU map
with a single -1 entry) by immediately returning true,
ensuring legitimate warnings are still reported.

Example before/after:

$ perf stat -M lpm_miss_lat --metric-only --per-socket -a -- sleep 1

Before:
 Performance counter stats for 'system wide':

       ns  lpm_miss_lat_rem ns  lpm_miss_lat_loc
S0      126                202.3               207.9
S1      126                231.9               259.3

       1.006029831 seconds time elapsed

Some events weren't counted. Try disabling the NMI watchdog:
        echo 0 > /proc/sys/kernel/nmi_watchdog
        perf stat ...
        echo 1 > /proc/sys/kernel/nmi_watchdog

After:
 Performance counter stats for 'system wide':

       ns  lpm_miss_lat_rem ns  lpm_miss_lat_loc
S0      126                202.3               207.9
S1      126                231.9               259.3

       1.006029831 seconds time elapsed

Assisted-by: Gemini:gemini-next
Signed-off-by: Chun-Tse Shao <ctshao@xxxxxxxxxx>
---
 tools/perf/util/stat-display.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index 2b69d238858c..e50557964916 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -792,6 +792,28 @@ static bool evlist__has_hybrid_pmus(struct evlist *evlist)
 	return false;
 }
 
+static bool evsel__should_run_on_aggr(struct perf_stat_config *config,
+				      struct evsel *counter,
+				      const struct aggr_cpu_id *id)
+{
+	struct perf_cpu cpu;
+	unsigned int idx;
+
+	if (!config->aggr_map || !config->aggr_get_id)
+		return true;
+
+	perf_cpu_map__for_each_cpu(cpu, idx, counter->core.cpus) {
+		struct aggr_cpu_id own_id;
+
+		if (cpu.cpu < 0)
+			return true;
+
+		own_id = config->aggr_get_id(config, cpu);
+		if (aggr_cpu_id__equal(id, &own_id))
+			return true;
+	}
+	return false;
+}
 static void printout(struct perf_stat_config *config, struct outstate *os,
 		     double uval, u64 run, u64 ena, double noise, int aggr_idx)
 {
@@ -822,7 +844,8 @@ static void printout(struct perf_stat_config *config, struct outstate *os,
 
 		if (counter->supported) {
 			if (!evlist__has_hybrid_pmus(counter->evlist)) {
-				config->print_free_counters_hint = 1;
+				if (evsel__should_run_on_aggr(config, counter, &os->id))
+					config->print_free_counters_hint = 1;
 			}
 		}
 	}
-- 
2.54.0.1099.g489fc7bff1-goog