[PATCH v2 2/2] perf parse-events: Architecture specific leader override

[Ian Rogers]

Currently topdown events must appear after a slots event:

$ perf stat -e '{slots,topdown-fe-bound}' /bin/true

 Performance counter stats for '/bin/true':

         3,183,090      slots
           986,133      topdown-fe-bound

Reversing the events yields:

$ perf stat -e '{topdown-fe-bound,slots}' /bin/true
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (topdown-fe-bound).

For metrics the order of events is determined by iterating over a
hashmap, and so slots isn't guaranteed to be first which can yield this
error.

Change the set_leader in parse-events, called when a group is closed, so
that rather than always making the first event the leader, if the slots
event exists then it is made the leader. It is then moved to the head of
the evlist otherwise it won't be opened in the correct order.

The result is:

$ perf stat -e '{topdown-fe-bound,slots}' /bin/true

 Performance counter stats for '/bin/true':

         3,274,795      slots
         1,001,702      topdown-fe-bound

A problem with this approach is the slots event is identified by name,
names can be overwritten like 'cpu/slots,name=foo/' and this causes the
leader change to fail.

The change also modifies and fixes mixed groups like, with the change:

$ perf stat -e '{instructions,slots,topdown-fe-bound}' -a -- sleep 2

 Performance counter stats for 'system wide':

        5574985410      slots
         971981616      instructions
        1348461887      topdown-fe-bound

       2.001263120 seconds time elapsed

Without the change:

$ perf stat -e '{instructions,slots,topdown-fe-bound}' -a -- sleep 2

 Performance counter stats for 'system wide':

     <not counted>      instructions
     <not counted>      slots
   <not supported>      topdown-fe-bound

       2.006247990 seconds time elapsed

Something that may be undesirable here is that the events are reordered
in the output.

v2. Move the list_move operation into parse_events__set_leader as
    suggested by Jiri Olsa <jolsa@xxxxxxxxxx>.

Reviewed-by: Kajol Jain<kjain@xxxxxxxxxxxxx>
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/arch/x86/util/evlist.c | 17 +++++++++++++++++
 tools/perf/util/evlist.h          |  1 +
 tools/perf/util/parse-events.c    |  8 +++++++-
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/tools/perf/arch/x86/util/evlist.c b/tools/perf/arch/x86/util/evlist.c
index 0b0951030a2f..1624372b2da2 100644
--- a/tools/perf/arch/x86/util/evlist.c
+++ b/tools/perf/arch/x86/util/evlist.c
@@ -17,3 +17,20 @@ int arch_evlist__add_default_attrs(struct evlist *evlist)
 	else
 		return parse_events(evlist, TOPDOWN_L1_EVENTS, NULL);
 }
+
+struct evsel *arch_evlist__leader(struct list_head *list)
+{
+	struct evsel *evsel, *first;
+
+	first = list_entry(list->next, struct evsel, core.node);
+
+	if (!pmu_have_event("cpu", "slots"))
+		return first;
+
+	__evlist__for_each_entry(list, evsel) {
+		if (evsel->pmu_name && !strcmp(evsel->pmu_name, "cpu") &&
+			evsel->name && strstr(evsel->name, "slots"))
+			return evsel;
+	}
+	return first;
+}
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 97bfb8d0be4f..993437ffe429 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -110,6 +110,7 @@ int __evlist__add_default_attrs(struct evlist *evlist,
 	__evlist__add_default_attrs(evlist, array, ARRAY_SIZE(array))
 
 int arch_evlist__add_default_attrs(struct evlist *evlist);
+struct evsel *arch_evlist__leader(struct list_head *list);
 
 int evlist__add_dummy(struct evlist *evlist);
 
diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 6308ba739d19..774c163eae9c 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1821,6 +1821,11 @@ parse_events__set_leader_for_uncore_aliase(char *name, struct list_head *list,
 	return ret;
 }
 
+__weak struct evsel *arch_evlist__leader(struct list_head *list)
+{
+	return list_entry(list->next, struct evsel, core.node);
+}
+
 void parse_events__set_leader(char *name, struct list_head *list,
 			      struct parse_events_state *parse_state)
 {
@@ -1834,9 +1839,10 @@ void parse_events__set_leader(char *name, struct list_head *list,
 	if (parse_events__set_leader_for_uncore_aliase(name, list, parse_state))
 		return;
 
-	leader = list_entry(list->next, struct evsel, core.node);
+	leader = arch_evlist__leader(list);
 	__perf_evlist__set_leader(list, &leader->core);
 	leader->group_name = name ? strdup(name) : NULL;
+	list_move(&leader->core.node, list);
 }
 
 /* list_event is assumed to point to malloc'ed memory */
-- 
2.34.0.rc2.393.gf8c9666880-goog