[RFC PATCH v1] perf pmu: Assume sysfs events are always lowercase

[Ian Rogers]

Perf event names aren't case sensitive. For sysfs events the entire
directory of events is read then iterated comparing names in a case
insensitive way, most often to see if an event is present.

Consider:
$ perf stat -e inst_retired.any true

The event inst_retired.any may be present in any PMU, so every PMU's
sysfs events are loaded and then searched with strcasecmp to see if
any match. This event is only present on the cpu PMU as a json event
so a lot of events were loaded from sysfs unnecessarily just to prove
an event didn't exist there.

This change avoids loading all the events by assuming sysfs event
names are always lowercase. It then uses file exists and only loads
the events when the desired event is present.

For the example above, the number of openat calls measured by perf
trace on a tigerlake laptop goes from 325 down to 255. The reduction
will be larger for machines with many PMUs, particularly replicated
uncore PMUs.

Make pmu_aliases_parse early return when aliases are loaded, ensure
the function is called before all uses of the aliases list.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/pmu.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index ab30f22eaf10..ce72c99e4f61 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -425,9 +425,16 @@ static struct perf_pmu_alias *perf_pmu__find_alias(struct perf_pmu *pmu,
 {
 	struct perf_pmu_alias *alias;
 
-	if (load && !pmu->sysfs_aliases_loaded)
-		pmu_aliases_parse(pmu);
+	if (load && !pmu->sysfs_aliases_loaded) {
+		char event_file_name[FILENAME_MAX + 8];
 
+		scnprintf(event_file_name, sizeof(event_file_name), "events/%s", name);
+		for (size_t i = 7, n = 7 + strlen(name); i < n; i++)
+			event_file_name[i] = tolower(event_file_name[i]);
+
+		if (perf_pmu__file_exists(pmu, event_file_name))
+			pmu_aliases_parse(pmu);
+	}
 	list_for_each_entry(alias, &pmu->aliases, list) {
 		if (!strcasecmp(alias->name, name))
 			return alias;
@@ -605,6 +612,9 @@ static int pmu_aliases_parse(struct perf_pmu *pmu)
 	size_t len;
 	int fd, dir_fd;
 
+	if (pmu->sysfs_aliases_loaded)
+		return 0;
+
 	len = perf_pmu__event_source_devices_scnprintf(path, sizeof(path));
 	if (!len)
 		return 0;
@@ -1689,9 +1699,7 @@ size_t perf_pmu__num_events(struct perf_pmu *pmu)
 {
 	size_t nr;
 
-	if (!pmu->sysfs_aliases_loaded)
-		pmu_aliases_parse(pmu);
-
+	pmu_aliases_parse(pmu);
 	nr = pmu->sysfs_aliases;
 
 	if (pmu->cpu_aliases_added)
@@ -1750,6 +1758,7 @@ int perf_pmu__for_each_event(struct perf_pmu *pmu, bool skip_duplicate_pmus,
 	struct strbuf sb;
 
 	strbuf_init(&sb, /*hint=*/ 0);
+	pmu_aliases_parse(pmu);
 	pmu_add_cpu_aliases(pmu);
 	list_for_each_entry(event, &pmu->aliases, list) {
 		size_t buf_used;
@@ -2154,6 +2163,7 @@ const char *perf_pmu__name_from_config(struct perf_pmu *pmu, u64 config)
 	if (!pmu)
 		return NULL;
 
+	pmu_aliases_parse(pmu);
 	pmu_add_cpu_aliases(pmu);
 	list_for_each_entry(event, &pmu->aliases, list) {
 		struct perf_event_attr attr = {.config = 0,};
-- 
2.44.0.683.g7961c838ac-goog