mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-05 10:29:37 +00:00
d96645821e
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>
63 lines
1.2 KiB
C
63 lines
1.2 KiB
C
// 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;
|
|
}
|