[RFC PATCH 6/7] perf metricgroup: order event groups by size

[Ian Rogers <irogers@google.com>]

When adding event groups to the group list, insert them in size order.
This performs an insertion sort on the group list. By placing the
largest groups at the front of the group list it is possible to see if a
larger group contains the same events as a later group. This can make
the later group redundant - it can reuse the events from the large group.
A later patch will add this sharing.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/metricgroup.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
index 0a00c0f87872..25e3e8df6b45 100644
--- a/tools/perf/util/metricgroup.c
+++ b/tools/perf/util/metricgroup.c
@@ -519,7 +519,21 @@ static int __metricgroup__add_metric(struct list_head *group_list,
 		return -EINVAL;
 	}
 
-	list_add_tail(&eg->nd, group_list);
+	if (list_empty(group_list))
+		list_add(&eg->nd, group_list);
+	else {
+		struct list_head *pos;
+
+		/* Place the largest groups at the front. */
+		list_for_each_prev(pos, group_list) {
+			struct egroup *old = list_entry(pos, struct egroup, nd);
+
+			if (hashmap__size(&eg->pctx.ids) <=
+			    hashmap__size(&old->pctx.ids))
+				break;
+		}
+		list_add(&eg->nd, pos);
+	}
 
 	return 0;
 }
-- 
2.26.2.526.g744177e7f7-goog