Re: [PATCH v3 01/18] perf metricgroup: Add care to picking the evsel for displaying a metric

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 11/11/2025 12:04 PM, Ian Rogers wrote:
> Rather than using the first evsel in the matched events, try to find
> the least shared non-tool evsel. The aim is to pick the first evsel
> that typifies the metric within the list of metrics.
>
> This addresses an issue where Default metric group metrics may lose
> their counter value due to how the stat displaying hides counters for
> default event/metric output.
>
> For a metricgroup like TopdownL1 on an Intel Alderlake the change is,
> before there are 4 events with metrics:
> ```
> $ perf stat -M topdownL1 -a sleep 1
>
>  Performance counter stats for 'system wide':
>
>      7,782,334,296      cpu_core/TOPDOWN.SLOTS/          #     10.4 %  tma_bad_speculation
>                                                   #     19.7 %  tma_frontend_bound
>      2,668,927,977      cpu_core/topdown-retiring/       #     35.7 %  tma_backend_bound
>                                                   #     34.1 %  tma_retiring
>        803,623,987      cpu_core/topdown-bad-spec/
>        167,514,386      cpu_core/topdown-heavy-ops/
>      1,555,265,776      cpu_core/topdown-fe-bound/
>      2,792,733,013      cpu_core/topdown-be-bound/
>        279,769,310      cpu_atom/TOPDOWN_RETIRING.ALL/   #     12.2 %  tma_retiring
>                                                   #     15.1 %  tma_bad_speculation
>        457,917,232      cpu_atom/CPU_CLK_UNHALTED.CORE/  #     38.4 %  tma_backend_bound
>                                                   #     34.2 %  tma_frontend_bound
>        783,519,226      cpu_atom/TOPDOWN_FE_BOUND.ALL/
>         10,790,192      cpu_core/INT_MISC.UOP_DROPPING/
>        879,845,633      cpu_atom/TOPDOWN_BE_BOUND.ALL/
> ```
>
> After there are 6 events with metrics:
> ```
> $ perf stat -M topdownL1 -a sleep 1
>
>  Performance counter stats for 'system wide':
>
>      2,377,551,258      cpu_core/TOPDOWN.SLOTS/          #      7.9 %  tma_bad_speculation
>                                                   #     36.4 %  tma_frontend_bound
>        480,791,142      cpu_core/topdown-retiring/       #     35.5 %  tma_backend_bound
>        186,323,991      cpu_core/topdown-bad-spec/
>         65,070,590      cpu_core/topdown-heavy-ops/      #     20.1 %  tma_retiring
>        871,733,444      cpu_core/topdown-fe-bound/
>        848,286,598      cpu_core/topdown-be-bound/
>        260,936,456      cpu_atom/TOPDOWN_RETIRING.ALL/   #     12.4 %  tma_retiring
>                                                   #     17.6 %  tma_bad_speculation
>        419,576,513      cpu_atom/CPU_CLK_UNHALTED.CORE/
>        797,132,597      cpu_atom/TOPDOWN_FE_BOUND.ALL/   #     38.0 %  tma_frontend_bound
>          3,055,447      cpu_core/INT_MISC.UOP_DROPPING/
>        671,014,164      cpu_atom/TOPDOWN_BE_BOUND.ALL/   #     32.0 %  tma_backend_bound
> ```

It looks the output of cpu_core and cpu_atom events are mixed together,
like the "cpu_core/INT_MISC.UOP_DROPPING/". Could we resort the events and
separate the cpu_core and cpu_atom events output? It would make the output
more read-friendly. Thanks.


>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/util/metricgroup.c | 48 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
> index 48936e517803..76092ee26761 100644
> --- a/tools/perf/util/metricgroup.c
> +++ b/tools/perf/util/metricgroup.c
> @@ -1323,6 +1323,51 @@ static int parse_ids(bool metric_no_merge, bool fake_pmu,
>  	return ret;
>  }
>  
> +/* How many times will a given evsel be used in a set of metrics? */
> +static int count_uses(struct list_head *metric_list, struct evsel *evsel)
> +{
> +	const char *metric_id = evsel__metric_id(evsel);
> +	struct metric *m;
> +	int uses = 0;
> +
> +	list_for_each_entry(m, metric_list, nd) {
> +		if (hashmap__find(m->pctx->ids, metric_id, NULL))
> +			uses++;
> +	}
> +	return uses;
> +}
> +
> +/*
> + * Select the evsel that stat-display will use to trigger shadow/metric
> + * printing. Pick the least shared non-tool evsel, encouraging metrics to be
> + * with a hardware counter that is specific to them.
> + */
> +static struct evsel *pick_display_evsel(struct list_head *metric_list,
> +					struct evsel **metric_events)
> +{
> +	struct evsel *selected = metric_events[0];
> +	size_t selected_uses;
> +	bool selected_is_tool;
> +
> +	if (!selected)
> +		return NULL;
> +
> +	selected_uses = count_uses(metric_list, selected);
> +	selected_is_tool = evsel__is_tool(selected);
> +	for (int i = 1; metric_events[i]; i++) {
> +		struct evsel *candidate = metric_events[i];
> +		size_t candidate_uses = count_uses(metric_list, candidate);
> +
> +		if ((selected_is_tool && !evsel__is_tool(candidate)) ||
> +		    (candidate_uses < selected_uses)) {
> +			selected = candidate;
> +			selected_uses = candidate_uses;
> +			selected_is_tool = evsel__is_tool(selected);
> +		}
> +	}
> +	return selected;
> +}
> +
>  static int parse_groups(struct evlist *perf_evlist,
>  			const char *pmu, const char *str,
>  			bool metric_no_group,
> @@ -1430,7 +1475,8 @@ static int parse_groups(struct evlist *perf_evlist,
>  			goto out;
>  		}
>  
> -		me = metricgroup__lookup(&perf_evlist->metric_events, metric_events[0],
> +		me = metricgroup__lookup(&perf_evlist->metric_events,
> +					 pick_display_evsel(&metric_list, metric_events),
>  					 /*create=*/true);
>  
>  		expr = malloc(sizeof(struct metric_expr));