linux-kernel - [PATCH v2] perf parse-events: Make X modifier more respectful of groups

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Message-ID: <20251017230357.15663-1-irogers@google.com>
Date: Fri, 17 Oct 2025 16:03:57 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Thomas Falcon <thomas.falcon@...el.com>, Dapeng Mi <dapeng1.mi@...ux.intel.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] perf parse-events: Make X modifier more respectful of groups

Events with an X modifier were reordered within a group, for example
slots was made the leader in:
```
$ perf record -e '{cpu/mem-stores/ppu,cpu/slots/uX}' -- sleep 1
```

Fix by making `dont_regroup` evsels always use their index for
sorting. Make the cur_leader, when fixing the groups, be that of
`dont_regroup` evsel so that the `dont_regroup` evsel doesn't become a
leader.

On a tigerlake this patch corrects this and meets expectations in:
```
$ perf stat -e '{cpu/mem-stores/,cpu/slots/uX}' -a -- sleep 0.1

 Performance counter stats for 'system wide':

        83,458,652      cpu/mem-stores/
     2,720,854,880      cpu/slots/uX

       0.103780587 seconds time elapsed

$ perf stat -e 'slots,slots:X' -a -- sleep 0.1

 Performance counter stats for 'system wide':

       732,042,247      slots                (48.96%)
       643,288,155      slots:X              (51.04%)

       0.102731018 seconds time elapsed
```

Closes: https://lore.kernel.org/lkml/18f20d38-070c-4e17-bc90-cf7102e1e53d@linux.intel.com/
Fixes: 035c17893082 ("perf parse-events: Add 'X' modifier to exclude an event from being regrouped")
Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/parse-events.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 3aec86aebdc6..0c0dc20b1c13 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1973,14 +1973,18 @@ static int evlist__cmp(void *_fg_idx, const struct list_head *l, const struct li
 	 * event's index is used. An index may be forced for events that
 	 * must be in the same group, namely Intel topdown events.
 	 */
-	if (*force_grouped_idx != -1 && arch_evsel__must_be_in_group(lhs)) {
+	if (lhs->dont_regroup) {
+		lhs_sort_idx = lhs_core->idx;
+	} else if (*force_grouped_idx != -1 && arch_evsel__must_be_in_group(lhs)) {
 		lhs_sort_idx = *force_grouped_idx;
 	} else {
 		bool lhs_has_group = lhs_core->leader != lhs_core || lhs_core->nr_members > 1;
 
 		lhs_sort_idx = lhs_has_group ? lhs_core->leader->idx : lhs_core->idx;
 	}
-	if (*force_grouped_idx != -1 && arch_evsel__must_be_in_group(rhs)) {
+	if (rhs->dont_regroup) {
+		rhs_sort_idx = rhs_core->idx;
+	} else if (*force_grouped_idx != -1 && arch_evsel__must_be_in_group(rhs)) {
 		rhs_sort_idx = *force_grouped_idx;
 	} else {
 		bool rhs_has_group = rhs_core->leader != rhs_core || rhs_core->nr_members > 1;
@@ -2078,10 +2082,10 @@ static int parse_events__sort_events_and_fix_groups(struct list_head *list)
 	 */
 	idx = 0;
 	list_for_each_entry(pos, list, core.node) {
-		const struct evsel *pos_leader = evsel__leader(pos);
+		struct evsel *pos_leader = evsel__leader(pos);
 		const char *pos_pmu_name = pos->group_pmu_name;
 		const char *cur_leader_pmu_name;
-		bool pos_force_grouped = force_grouped_idx != -1 &&
+		bool pos_force_grouped = force_grouped_idx != -1 && !pos->dont_regroup &&
 			arch_evsel__must_be_in_group(pos);
 
 		/* Reset index and nr_members. */
@@ -2095,8 +2099,8 @@ static int parse_events__sort_events_and_fix_groups(struct list_head *list)
 		 * groups can't span PMUs.
 		 */
 		if (!cur_leader || pos->dont_regroup) {
-			cur_leader = pos;
-			cur_leaders_grp = &pos->core;
+			cur_leader = pos->dont_regroup ? pos_leader : pos;
+			cur_leaders_grp = &cur_leader->core;
 			if (pos_force_grouped)
 				force_grouped_leader = pos;
 		}
-- 
2.51.0.858.gf9c4a03a3a-goog