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

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