Commit d9664582 authored by Andi Kleen's avatar Andi Kleen Committed by Arnaldo Carvalho de Melo
Browse files

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: default avatarAndi Kleen <ak@linux.intel.com>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20191121001522.180827-2-andi@firstfloor.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 5b596e0f

tools/perf/util/Build

+1 −0
Original line number Diff line number Diff line
@@ -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

tools/perf/util/fncache.c

0 → 100644
+63 −0
Original line number Diff line number Diff line 
// 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;

}

tools/perf/util/fncache.h

0 → 100644
+7 −0
Original line number Diff line number Diff line 
#ifndef _FCACHE_H

#define _FCACHE_H 1



unsigned shash(const unsigned char *s);

bool file_available(const char *name);



#endif

tools/perf/util/pmu.c

+11 −23
Original line number Diff line number Diff line
@@ -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");

}

tools/perf/util/srccode.c

+1 −8
Original line number Diff line number Diff line
@@ -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;

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