perf pmu: Parse pmu caps sysfs only once

In addition to returning nr_caps, cache it locally in struct perf_pmu.

Similarly, cache status of whether caps sysfs has already been parsed
or not. These will help to avoid parsing sysfs every time the function
gets called.

Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ananth Narayan <ananth.narayan@amd.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kim Phillips <kim.phillips@amd.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <rrichter@amd.com>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Santosh Shukla <santosh.shukla@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: like.xu.linux@gmail.com
Cc: x86@kernel.org
Link: https://lore.kernel.org/r/20220604044519.594-3-ravi.bangoria@amd.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/pmu.c

@@ -1890,7 +1890,11 @@ int perf_pmu__caps_parse(struct perf_pmu *pmu)
 	const char *sysfs = sysfs__mountpoint();
 	DIR *caps_dir;
 	struct dirent *evt_ent;
-	int nr_caps = 0;
+
+	if (pmu->caps_initialized)
+		return pmu->nr_caps;
+
+	pmu->nr_caps = 0;
 
 	if (!sysfs)
 		return -1;
@@ -1898,8 +1902,10 @@ int perf_pmu__caps_parse(struct perf_pmu *pmu)
 	snprintf(caps_path, PATH_MAX,
 		 "%s" EVENT_SOURCE_DEVICE_PATH "%s/caps", sysfs, pmu->name);
 
-	if (stat(caps_path, &st) < 0)
+	if (stat(caps_path, &st) < 0) {
+		pmu->caps_initialized = true;
 		return 0;	/* no error if caps does not exist */
+	}
 
 	caps_dir = opendir(caps_path);
 	if (!caps_dir)
@@ -1926,13 +1932,14 @@ int perf_pmu__caps_parse(struct perf_pmu *pmu)
 			continue;
 		}
 
-		nr_caps++;
+		pmu->nr_caps++;
 		fclose(file);
 	}
 
 	closedir(caps_dir);
 
-	return nr_caps;
+	pmu->caps_initialized = true;
+	return pmu->nr_caps;
 }
 
 void perf_pmu__warn_invalid_config(struct perf_pmu *pmu, __u64 config,

tools/perf/util/pmu.h

@@ -46,6 +46,8 @@ struct perf_pmu {
 	struct perf_cpu_map *cpus;
 	struct list_head format;  /* HEAD struct perf_pmu_format -> list */
 	struct list_head aliases; /* HEAD struct perf_pmu_alias -> list */
+	bool caps_initialized;
+	u32 nr_caps;
 	struct list_head caps;    /* HEAD struct perf_pmu_caps -> list */
 	struct list_head list;    /* ELEM */
 	struct list_head hybrid_list;