[PATCH v1 1/5] perf stat: Better hybrid support for the NMI watchdog warning

Ian Rogers
2025-03-18T04:14:51Z

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@google.com>
---
tools/perf/util/stat-display.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index e852ac0d9847..f311f1960e29 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -825,13 +825,25 @@ static bool is_mixed_hw_group(struct evsel *counter)
static bool evlist__has_hybrid(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;
--
2.49.0.rc1.451.g8f38331e32-goog