[PATCH] perf metrics: Ensure at least 1 id per metric

[Ian Rogers]

We may have no events for a metric evaluated to a constant. In such a
case ensure a tool event is at least evaluated for metric parsing and
displaying.

Fixes: 8586d2744ff3 ("perf metrics: Don't add all tool events for sharing")
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/metricgroup.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
index ee8fcfa115e5..8f7baeabc5cf 100644
--- a/tools/perf/util/metricgroup.c
+++ b/tools/perf/util/metricgroup.c
@@ -1372,6 +1372,7 @@ static int parse_ids(bool metric_no_merge, struct perf_pmu *fake_pmu,
 
 	*out_evlist = NULL;
 	if (!metric_no_merge || hashmap__size(ids->ids) == 0) {
+		bool added_event = false;
 		int i;
 		/*
 		 * We may fail to share events between metrics because a tool
@@ -1393,8 +1394,16 @@ static int parse_ids(bool metric_no_merge, struct perf_pmu *fake_pmu,
 				if (!tmp)
 					return -ENOMEM;
 				ids__insert(ids->ids, tmp);
+				added_event = true;
 			}
 		}
+		if (!added_event && hashmap__size(ids->ids) == 0) {
+			char *tmp = strdup("duration_time");
+
+			if (!tmp)
+				return -ENOMEM;
+			ids__insert(ids->ids, tmp);
+		}
 	}
 	ret = metricgroup__build_event_string(&events, ids, modifier,
 					      has_constraint);
-- 
2.37.0.rc0.104.g0611611a94-goog