[PATCH v1 05/22] perf metricgroup: Add care to picking the evsel for displaying a metric

[Ian Rogers]

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.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 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));
-- 
2.51.1.821.gb6fe4d2222-goog