linux-kernel - [PATCH v5 2/8] perf tool: Parse pmu caps sysfs only once

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Date:   Wed, 1 Jun 2022 08:56:02 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     <acme@...nel.org>, <kan.liang@...ux.intel.com>
CC:     <ravi.bangoria@....com>, <jolsa@...nel.org>, <irogers@...gle.com>,
        <peterz@...radead.org>, <rrichter@....com>, <mingo@...hat.com>,
        <mark.rutland@....com>, <namhyung@...nel.org>,
        <tglx@...utronix.de>, <bp@...en8.de>, <james.clark@....com>,
        <leo.yan@...aro.org>, <ak@...ux.intel.com>, <eranian@...gle.com>,
        <like.xu.linux@...il.com>, <x86@...nel.org>,
        <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <sandipan.das@....com>, <ananth.narayan@....com>,
        <kim.phillips@....com>, <santosh.shukla@....com>
Subject: [PATCH v5 2/8] perf tool: 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.

Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
---
 tools/perf/util/pmu.c | 15 +++++++++++----
 tools/perf/util/pmu.h |  2 ++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 9a1c7e63e663..0112e1c36418 100644
--- a/tools/perf/util/pmu.c
+++ b/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,
diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
index 541889fa9f9c..4b45fd8da5a3 100644
--- a/tools/perf/util/pmu.h
+++ b/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;
-- 
2.31.1