[PATCH v4 31/35] perf pmus: Avoid repeated sysfs scanning

[Ian Rogers]

perf_pmus__scan will process every directory in sysfs to see if it is
a PMU, attempting to add it if not already in the pmus list. Add two
booleans to record whether this scanning has been done for core or all
PMUs. Skip scanning in the event that scanning has already occurred.

Signed-off-by: Ian Rogers <irogers at google.com>
Reviewed-by: Kan Liang <kan.liang at linux.intel.com>
---
 tools/perf/util/pmus.c | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
index de7fc36519c9..2c512345191d 100644
--- a/tools/perf/util/pmus.c
+++ b/tools/perf/util/pmus.c
@@ -14,6 +14,8 @@
 
 static LIST_HEAD(core_pmus);
 static LIST_HEAD(other_pmus);
+static bool read_sysfs_core_pmus;
+static bool read_sysfs_all_pmus;
 
 void perf_pmus__destroy(void)
 {
@@ -29,6 +31,8 @@ void perf_pmus__destroy(void)
 
 		perf_pmu__delete(pmu);
 	}
+	read_sysfs_core_pmus = false;
+	read_sysfs_all_pmus = false;
 }
 
 static struct perf_pmu *pmu_find(const char *name)
@@ -53,6 +57,7 @@ struct perf_pmu *perf_pmus__find(const char *name)
 {
 	struct perf_pmu *pmu;
 	int dirfd;
+	bool core_pmu;
 
 	/*
 	 * Once PMU is loaded it stays in the list,
@@ -63,8 +68,15 @@ struct perf_pmu *perf_pmus__find(const char *name)
 	if (pmu)
 		return pmu;
 
+	if (read_sysfs_all_pmus)
+		return NULL;
+
+	core_pmu = is_pmu_core(name);
+	if (core_pmu && read_sysfs_core_pmus)
+		return NULL;
+
 	dirfd = perf_pmu__event_source_devices_fd();
-	pmu = perf_pmu__lookup(is_pmu_core(name) ? &core_pmus : &other_pmus, dirfd, name);
+	pmu = perf_pmu__lookup(core_pmu ? &core_pmus : &other_pmus, dirfd, name);
 	close(dirfd);
 
 	return pmu;
@@ -73,6 +85,7 @@ struct perf_pmu *perf_pmus__find(const char *name)
 static struct perf_pmu *perf_pmu__find2(int dirfd, const char *name)
 {
 	struct perf_pmu *pmu;
+	bool core_pmu;
 
 	/*
 	 * Once PMU is loaded it stays in the list,
@@ -83,7 +96,14 @@ static struct perf_pmu *perf_pmu__find2(int dirfd, const char *name)
 	if (pmu)
 		return pmu;
 
-	return perf_pmu__lookup(is_pmu_core(name) ? &core_pmus : &other_pmus, dirfd, name);
+	if (read_sysfs_all_pmus)
+		return NULL;
+
+	core_pmu = is_pmu_core(name);
+	if (core_pmu && read_sysfs_core_pmus)
+		return NULL;
+
+	return perf_pmu__lookup(core_pmu ? &core_pmus : &other_pmus, dirfd, name);
 }
 
 /* Add all pmus in sysfs to pmu list: */
@@ -93,6 +113,9 @@ static void pmu_read_sysfs(bool core_only)
 	DIR *dir;
 	struct dirent *dent;
 
+	if (read_sysfs_all_pmus || (core_only && read_sysfs_core_pmus))
+		return;
+
 	fd = perf_pmu__event_source_devices_fd();
 	if (fd < 0)
 		return;
@@ -111,6 +134,12 @@ static void pmu_read_sysfs(bool core_only)
 	}
 
 	closedir(dir);
+	if (core_only) {
+		read_sysfs_core_pmus = true;
+	} else {
+		read_sysfs_core_pmus = true;
+		read_sysfs_all_pmus = true;
+	}
 }
 
 struct perf_pmu *perf_pmus__find_by_type(unsigned int type)
-- 
2.41.0.rc0.172.g3f132b7071-goog