[PATCH v5 01/13] perf pmu: Use file system cache to optimize sysfs access

Andi Kleen
2019-11-07T18:17:23Z

From: Andi Kleen <ak@linux.intel.com>

pmu.c does a lot of redundant /sys accesses while parsing aliases
and probing for PMUs. On large systems with a lot of PMUs this
can get expensive (>2s):

% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
27.25 1.227847 8 160888 16976 openat
26.42 1.190481 7 164224 164077 stat

Add a cache to remember if specific file names exist or don't
exist, which eliminates most of this overhead.

Also optimize some stat() calls to be slightly cheaper access()

Resulting in:

0.18 0.004166 2 1851 305 open
0.08 0.001970 2 829 622 access

Signed-off-by: Andi Kleen <ak@linux.intel.com>

---

v2: Use single lookup function as API (Jiri)
---
tools/perf/util/Build | 1 +
tools/perf/util/fncache.c | 63 +++++++++++++++++++++++++++++++++++++++
tools/perf/util/fncache.h | 7 +++++
tools/perf/util/pmu.c | 34 +++++++--------------
tools/perf/util/srccode.c | 9 +-----
5 files changed, 83 insertions(+), 31 deletions(-)
create mode 100644 tools/perf/util/fncache.c
create mode 100644 tools/perf/util/fncache.h

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 39814b1806a6..2c1504fe924c 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -48,6 +48,7 @@ perf-y += header.o
perf-y += callchain.o
perf-y += values.o
perf-y += debug.o
+perf-y += fncache.o
perf-y += machine.o
perf-y += map.o
perf-y += pstack.o
diff --git a/tools/perf/util/fncache.c b/tools/perf/util/fncache.c
new file mode 100644
index 000000000000..5afcd7edbe7a
--- /dev/null
+++ b/tools/perf/util/fncache.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Manage a cache of file names' existence */
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <linux/list.h>
+#include "fncache.h"
+
+struct fncache {
+ struct hlist_node nd;
+ bool res;
+ char name[];
+};
+
+#define FNHSIZE 61
+
+static struct hlist_head fncache_hash[FNHSIZE];
+
+unsigned shash(const unsigned char *s)
+{
+ unsigned h = 0;
+ while (*s)
+ h = 65599 * h + *s++;
+ return h ^ (h >> 16);
+}
+
+static bool lookup_fncache(const char *name, bool *res)
+{
+ int h = shash((const unsigned char *)name) % FNHSIZE;
+ struct fncache *n;
+
+ hlist_for_each_entry (n, &fncache_hash[h], nd) {
+ if (!strcmp(n->name, name)) {
+ *res = n->res;
+ return true;
+ }
+ }
+ return false;
+}
+
+static void update_fncache(const char *name, bool res)
+{
+ struct fncache *n = malloc(sizeof(struct fncache) + strlen(name) + 1);
+ int h = shash((const unsigned char *)name) % FNHSIZE;
+
+ if (!n)
+ return;
+ strcpy(n->name, name);
+ n->res = res;
+ hlist_add_head(&n->nd, &fncache_hash[h]);
+}
+
+/* No LRU, only use when bounded in some other way. */
+bool file_available(const char *name)
+{
+ bool res;
+
+ if (lookup_fncache(name, &res))
+ return res;
+ res = access(name, R_OK) == 0;
+ update_fncache(name, res);
+ return res;
+}
diff --git a/tools/perf/util/fncache.h b/tools/perf/util/fncache.h
new file mode 100644
index 000000000000..fe020beaefb1
--- /dev/null
+++ b/tools/perf/util/fncache.h
@@ -0,0 +1,7 @@
+#ifndef _FCACHE_H
+#define _FCACHE_H 1
+
+unsigned shash(const unsigned char *s);
+bool file_available(const char *name);
+
+#endif
diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index adbe97e941dd..81357cc3d59a 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -24,6 +24,7 @@
#include "pmu-events/pmu-events.h"
#include "string2.h"
#include "strbuf.h"
+#include "fncache.h"

struct perf_pmu_format {
char *name;
@@ -82,7 +83,6 @@ int perf_pmu__format_parse(char *dir, struct list_head *head)
*/
static int pmu_format(const char *name, struct list_head *format)
{
- struct stat st;
char path[PATH_MAX];
const char *sysfs = sysfs__mountpoint();

@@ -92,8 +92,8 @@ static int pmu_format(const char *name, struct list_head *format)
snprintf(path, PATH_MAX,
"%s" EVENT_SOURCE_DEVICE_PATH "%s/format", sysfs, name);

- if (stat(path, &st) < 0)
- return 0; /* no error if format does not exist */
+ if (!file_available(path))
+ return 0;

if (perf_pmu__format_parse(path, format))
return -1;
@@ -475,7 +475,6 @@ static int pmu_aliases_parse(char *dir, struct list_head *head)
*/
static int pmu_aliases(const char *name, struct list_head *head)
{
- struct stat st;
char path[PATH_MAX];
const char *sysfs = sysfs__mountpoint();

@@ -485,8 +484,8 @@ static int pmu_aliases(const char *name, struct list_head *head)
snprintf(path, PATH_MAX,
"%s/bus/event_source/devices/%s/events", sysfs, name);

- if (stat(path, &st) < 0)
- return 0; /* no error if 'events' does not exist */
+ if (!file_available(path))
+ return 0;

if (pmu_aliases_parse(path, head))
return -1;
@@ -525,7 +524,6 @@ static int pmu_alias_terms(struct perf_pmu_alias *alias,
*/
static int pmu_type(const char *name, __u32 *type)
{
- struct stat st;
char path[PATH_MAX];
FILE *file;
int ret = 0;
@@ -537,7 +535,7 @@ static int pmu_type(const char *name, __u32 *type)
snprintf(path, PATH_MAX,
"%s" EVENT_SOURCE_DEVICE_PATH "%s/type", sysfs, name);

- if (stat(path, &st) < 0)
+ if (access(path, R_OK) < 0)
return -1;

file = fopen(path, "r");
@@ -628,14 +626,11 @@ static struct perf_cpu_map *pmu_cpumask(const char *name)
static bool pmu_is_uncore(const char *name)
{
char path[PATH_MAX];
- struct perf_cpu_map *cpus;
- const char *sysfs = sysfs__mountpoint();
+ const char *sysfs;

+ sysfs = sysfs__mountpoint();
snprintf(path, PATH_MAX, CPUS_TEMPLATE_UNCORE, sysfs, name);
- cpus = __pmu_cpumask(path);
- perf_cpu_map__put(cpus);
-
- return !!cpus;
+ return file_available(path);
}

/*
@@ -645,7 +640,6 @@ static bool pmu_is_uncore(const char *name)
*/
static int is_arm_pmu_core(const char *name)
{
- struct stat st;
char path[PATH_MAX];
const char *sysfs = sysfs__mountpoint();

@@ -655,10 +649,7 @@ static int is_arm_pmu_core(const char *name)
/* Look for cpu sysfs (specific to arm) */
scnprintf(path, PATH_MAX, "%s/bus/event_source/devices/%s/cpus",
sysfs, name);
- if (stat(path, &st) == 0)
- return 1;
-
- return 0;
+ return file_available(path);
}

static char *perf_pmu__getcpuid(struct perf_pmu *pmu)
@@ -1528,7 +1519,6 @@ bool pmu_have_event(const char *pname, const char *name)

static FILE *perf_pmu__open_file(struct perf_pmu *pmu, const char *name)
{
- struct stat st;
char path[PATH_MAX];
const char *sysfs;

@@ -1538,10 +1528,8 @@ static FILE *perf_pmu__open_file(struct perf_pmu *pmu, const char *name)

snprintf(path, PATH_MAX,
"%s" EVENT_SOURCE_DEVICE_PATH "%s/%s", sysfs, pmu->name, name);
-
- if (stat(path, &st) < 0)
+ if (!file_available(path))
return NULL;
-
return fopen(path, "r");
}

diff --git a/tools/perf/util/srccode.c b/tools/perf/util/srccode.c
index d84ed8b6caaa..c29edaaca863 100644
--- a/tools/perf/util/srccode.c
+++ b/tools/perf/util/srccode.c
@@ -16,6 +16,7 @@
#include "srccode.h"
#include "debug.h"
#include <internal/lib.h> // page_size
+#include "fncache.h"

#define MAXSRCCACHE (32*1024*1024)
#define MAXSRCFILES 64
@@ -36,14 +37,6 @@ static LIST_HEAD(srcfile_list);
static long map_total_sz;
static int num_srcfiles;

-static unsigned shash(unsigned char *s)
-{
- unsigned h = 0;
- while (*s)
- h = 65599 * h + *s++;
- return h ^ (h >> 16);
-}
-
static int countlines(char *map, int maplen)
{
int numl;
--
2.23.0