linux-kernel - [PATCH v2 1/5] perf stat: Better hybrid support for the NMI watchdog warning

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Message-ID: <20250402164720.3847573-2-irogers@google.com>
Date: Wed,  2 Apr 2025 09:47:16 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, Howard Chu <howardchu95@...il.com>, 
	Dominique Martinet <asmadeus@...ewreck.org>, Levi Yun <yeoreum.yun@....com>, 
	"Dr. David Alan Gilbert" <linux@...blig.org>, Andi Kleen <ak@...ux.intel.com>, 
	James Clark <james.clark@...aro.org>, Weilin Wang <weilin.wang@...el.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/5] perf stat: Better hybrid support for the NMI watchdog warning

Prior to this patch evlist__has_hybrid would return false if the
processor wasn't hybrid or the evlist didn't contain any core
events. If the only PMU used by events was cpu_core then it would
true even though there are no cpu_atom events. For example:

```
$ perf stat --cputype=cpu_core -e '{cycles,cycles,cycles,cycles,cycles,cycles,cycles,cycles,cycles}' true

 Performance counter stats for 'true':

     <not counted>      cpu_core/cycles/                                                        (0.00%)
     <not counted>      cpu_core/cycles/                                                        (0.00%)
     <not counted>      cpu_core/cycles/                                                        (0.00%)
     <not counted>      cpu_core/cycles/                                                        (0.00%)
     <not counted>      cpu_core/cycles/                                                        (0.00%)
     <not counted>      cpu_core/cycles/                                                        (0.00%)
     <not counted>      cpu_core/cycles/                                                        (0.00%)
     <not counted>      cpu_core/cycles/                                                        (0.00%)
     <not counted>      cpu_core/cycles/                                                        (0.00%)

       0.001981900 seconds time elapsed

       0.002311000 seconds user
       0.000000000 seconds sys
```

This patch changes evlist__has_hybrid to return true only if the
evlist contains events from >1 core PMU. This means the NMI watchdog
warning is shown for the case above.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/stat-display.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index e852ac0d9847..1115efb380fb 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -822,16 +822,28 @@ static bool is_mixed_hw_group(struct evsel *counter)
 	return false;
 }
 
-static bool evlist__has_hybrid(struct evlist *evlist)
+static bool evlist__has_hybrid_pmus(struct evlist *evlist)
 {
 	struct evsel *evsel;
+	struct perf_pmu *last_core_pmu = NULL;
 
 	if (perf_pmus__num_core_pmus() == 1)
 		return false;
 
 	evlist__for_each_entry(evlist, evsel) {
-		if (evsel->core.is_pmu_core)
+		if (evsel->core.is_pmu_core) {
+			struct perf_pmu *pmu = evsel__find_pmu(evsel);
+
+			if (pmu == last_core_pmu)
+				continue;
+
+			if (last_core_pmu == NULL) {
+				last_core_pmu = pmu;
+				continue;
+			}
+			/* A distinct core PMU. */
 			return true;
+		}
 	}
 
 	return false;
@@ -872,7 +884,7 @@ static void printout(struct perf_stat_config *config, struct outstate *os,
 		ok = false;
 
 		if (counter->supported) {
-			if (!evlist__has_hybrid(counter->evlist)) {
+			if (!evlist__has_hybrid_pmus(counter->evlist)) {
 				config->print_free_counters_hint = 1;
 				if (is_mixed_hw_group(counter))
 					config->print_mixed_hw_group_error = 1;
-- 
2.49.0.504.g3bcea36a83-goog