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

[Liang, Kan]

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@xxxxxxxxxx>
> ---
>  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;