perf pmus: Make PMU alias name loading lazy

PMU alias names were computed when the first perf_pmu is created,
scanning all PMUs in event sources for a file called alias that
generally doesn't exist. Switch to trying to load the file when all
PMU related files are loaded in lookup. This would cause a PMU name
lookup of an alias name to fail if no PMUs were loaded, so in that
case all PMUs are loaded and the find repeated. The overhead is
similar but in the (very) general case not all PMUs are scanned for
the alias file.

As the overhead occurs once per invocation it doesn't show in perf
bench internals pmu-scan. On a tigerlake machine, the number of openat
system calls for an event of cpu/cycles/ with perf stat reduces from
94 to 69 (ie 25 fewer openat calls).
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: James Clark <james.clark@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/r/20230925062323.840799-1-irogers@google.comSigned-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/arch/x86/util/pmu.c

@@ -17,15 +17,6 @@
 #include "../../../util/pmus.h"
 #include "env.h"
 
-struct pmu_alias {
-	char *name;
-	char *alias;
-	struct list_head list;
-};
-
-static LIST_HEAD(pmu_alias_name_list);
-static bool cached_list;
-
 struct perf_event_attr *perf_pmu__get_default_config(struct perf_pmu *pmu __maybe_unused)
 {
 #ifdef HAVE_AUXTRACE_SUPPORT
@@ -41,136 +32,6 @@ struct perf_event_attr *perf_pmu__get_default_config(struct perf_pmu *pmu __mayb
 	return NULL;
 }
 
-static void pmu_alias__delete(struct pmu_alias *pmu_alias)
-{
-	if (!pmu_alias)
-		return;
-
-	zfree(&pmu_alias->name);
-	zfree(&pmu_alias->alias);
-	free(pmu_alias);
-}
-
-static struct pmu_alias *pmu_alias__new(char *name, char *alias)
-{
-	struct pmu_alias *pmu_alias = zalloc(sizeof(*pmu_alias));
-
-	if (pmu_alias) {
-		pmu_alias->name = strdup(name);
-		if (!pmu_alias->name)
-			goto out_delete;
-
-		pmu_alias->alias = strdup(alias);
-		if (!pmu_alias->alias)
-			goto out_delete;
-	}
-	return pmu_alias;
-
-out_delete:
-	pmu_alias__delete(pmu_alias);
-	return NULL;
-}
-
-static int setup_pmu_alias_list(void)
-{
-	int fd, dirfd;
-	DIR *dir;
-	struct dirent *dent;
-	struct pmu_alias *pmu_alias;
-	char buf[MAX_PMU_NAME_LEN];
-	FILE *file;
-	int ret = -ENOMEM;
-
-	dirfd = perf_pmu__event_source_devices_fd();
-	if (dirfd < 0)
-		return -1;
-
-	dir = fdopendir(dirfd);
-	if (!dir)
-		return -errno;
-
-	while ((dent = readdir(dir))) {
-		if (!strcmp(dent->d_name, ".") ||
-		    !strcmp(dent->d_name, ".."))
-			continue;
-
-		fd = perf_pmu__pathname_fd(dirfd, dent->d_name, "alias", O_RDONLY);
-		if (fd < 0)
-			continue;
-
-		file = fdopen(fd, "r");
-		if (!file)
-			continue;
-
-		if (!fgets(buf, sizeof(buf), file)) {
-			fclose(file);
-			continue;
-		}
-
-		fclose(file);
-
-		/* Remove the last '\n' */
-		buf[strlen(buf) - 1] = 0;
-
-		pmu_alias = pmu_alias__new(dent->d_name, buf);
-		if (!pmu_alias)
-			goto close_dir;
-
-		list_add_tail(&pmu_alias->list, &pmu_alias_name_list);
-	}
-
-	ret = 0;
-
-close_dir:
-	closedir(dir);
-	return ret;
-}
-
-static const char *__pmu_find_real_name(const char *name)
-{
-	struct pmu_alias *pmu_alias;
-
-	list_for_each_entry(pmu_alias, &pmu_alias_name_list, list) {
-		if (!strcmp(name, pmu_alias->alias))
-			return pmu_alias->name;
-	}
-
-	return name;
-}
-
-const char *pmu_find_real_name(const char *name)
-{
-	if (cached_list)
-		return __pmu_find_real_name(name);
-
-	setup_pmu_alias_list();
-	cached_list = true;
-
-	return __pmu_find_real_name(name);
-}
-
-static const char *__pmu_find_alias_name(const char *name)
-{
-	struct pmu_alias *pmu_alias;
-
-	list_for_each_entry(pmu_alias, &pmu_alias_name_list, list) {
-		if (!strcmp(name, pmu_alias->name))
-			return pmu_alias->alias;
-	}
-	return NULL;
-}
-
-const char *pmu_find_alias_name(const char *name)
-{
-	if (cached_list)
-		return __pmu_find_alias_name(name);
-
-	setup_pmu_alias_list();
-	cached_list = true;
-
-	return __pmu_find_alias_name(name);
-}
-
 int perf_pmus__num_mem_pmus(void)
 {
 	/* AMD uses IBS OP pmu and not a core PMU for perf mem/c2c */

tools/perf/util/pmu.c

@@ -960,16 +960,27 @@ perf_pmu__get_default_config(struct perf_pmu *pmu __maybe_unused)
 	return NULL;
 }
 
-const char * __weak
-pmu_find_real_name(const char *name)
+static char *pmu_find_alias_name(struct perf_pmu *pmu, int dirfd)
 {
-	return name;
-}
+	FILE *file = perf_pmu__open_file_at(pmu, dirfd, "alias");
+	char *line = NULL;
+	size_t line_len = 0;
+	ssize_t ret;
 
-const char * __weak
-pmu_find_alias_name(const char *name __maybe_unused)
-{
-	return NULL;
+	if (!file)
+		return NULL;
+
+	ret = getline(&line, &line_len, file);
+	if (ret < 0) {
+		fclose(file);
+		return NULL;
+	}
+	/* Remove trailing newline. */
+	if (ret > 0 && line[ret - 1] == '\n')
+		line[--ret] = '\0';
+
+	fclose(file);
+	return line;
 }
 
 static int pmu_max_precise(int dirfd, struct perf_pmu *pmu)
@@ -980,12 +991,10 @@ static int pmu_max_precise(int dirfd, struct perf_pmu *pmu)
 	return max_precise;
 }
 
-struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char *lookup_name)
+struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char *name)
 {
 	struct perf_pmu *pmu;
 	__u32 type;
-	const char *name = pmu_find_real_name(lookup_name);
-	const char *alias_name;
 
 	pmu = zalloc(sizeof(*pmu));
 	if (!pmu)
@@ -1018,18 +1027,12 @@ struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char
 	pmu->is_core = is_pmu_core(name);
 	pmu->cpus = pmu_cpumask(dirfd, name, pmu->is_core);
 
-	alias_name = pmu_find_alias_name(name);
-	if (alias_name) {
-		pmu->alias_name = strdup(alias_name);
-		if (!pmu->alias_name)
-			goto err;
-	}
-
 	pmu->type = type;
 	pmu->is_uncore = pmu_is_uncore(dirfd, name);
 	if (pmu->is_uncore)
 		pmu->id = pmu_id(name);
 	pmu->max_precise = pmu_max_precise(dirfd, pmu);
+	pmu->alias_name = pmu_find_alias_name(pmu, dirfd);
 	pmu->events_table = perf_pmu__find_events_table(pmu);
 	pmu_add_sys_aliases(pmu);
 	list_add_tail(&pmu->list, pmus);

tools/perf/util/pmu.h

@@ -252,8 +252,6 @@ void perf_pmu__warn_invalid_formats(struct perf_pmu *pmu);
 
 int perf_pmu__match(const char *pattern, const char *name, const char *tok);
 
-const char *pmu_find_real_name(const char *name);
-const char *pmu_find_alias_name(const char *name);
 double perf_pmu__cpu_slots_per_cycle(void);
 int perf_pmu__event_source_devices_scnprintf(char *pathname, size_t size);
 int perf_pmu__pathname_scnprintf(char *buf, size_t size,

tools/perf/util/pmus.c

@@ -37,6 +37,8 @@ static LIST_HEAD(other_pmus);
 static bool read_sysfs_core_pmus;
 static bool read_sysfs_all_pmus;
 
+static void pmu_read_sysfs(bool core_only);
+
 int pmu_name_len_no_suffix(const char *str, unsigned long *num)
 {
 	int orig_len, len;
@@ -124,6 +126,14 @@ struct perf_pmu *perf_pmus__find(const char *name)
 	pmu = perf_pmu__lookup(core_pmu ? &core_pmus : &other_pmus, dirfd, name);
 	close(dirfd);
 
+	if (!pmu) {
+		/*
+		 * Looking up an inidividual PMU failed. This may mean name is
+		 * an alias, so read the PMUs from sysfs and try to find again.
+		 */
+		pmu_read_sysfs(core_pmu);
+		pmu = pmu_find(name);
+	}
 	return pmu;
 }