perf pmu: Use file system cache to optimize sysfs access

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>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20191121001522.180827-2-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index b8e05a147b2b81711bfe937b8b86d2d3ce2b0c47..aab05e2c01a52349aa5d8f1af8d1c1c6783eb2af 100644 (file)
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -49,6 +49,7 @@ 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 (file)
index 0000000..6225cbc
--- /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 (file)
index 0000000..fe020be
--- /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 e8d34898802607e26ccd930a7fb8bea5af65587a..8b99fd312aae642ed3ca9a422ca3bef8473e47ad 100644 (file)
--- 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)
@@ -1544,7 +1535,6 @@ 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;
 
@@ -1554,10 +1544,8 @@ 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 d84ed8b6caaa21bd5c32b937b099cb53e3007cec..c29edaaca8633e5539511abb457e5592ee7fbbf1 100644 (file)
--- 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;