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

Liang, Kan
2025-04-02T15:23:17Z

On 2025-03-18 12:14 a.m., Ian Rogers wrote:
> 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.

Nit:
The function name may still bring confusions.
It may be better to change the function name as well, e.g.,
evlist__has_hybrid_pmus()? It implies more than one PMU.

Thanks,
Kan>
> 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;