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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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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>
64 lines
1.2 KiB
C
64 lines
1.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Manage a cache of file names' existence */
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#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <linux/list.h>
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#include "fncache.h"
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struct fncache {
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struct hlist_node nd;
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bool res;
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char name[];
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};
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#define FNHSIZE 61
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static struct hlist_head fncache_hash[FNHSIZE];
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unsigned shash(const unsigned char *s)
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{
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unsigned h = 0;
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while (*s)
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h = 65599 * h + *s++;
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return h ^ (h >> 16);
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}
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static bool lookup_fncache(const char *name, bool *res)
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{
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int h = shash((const unsigned char *)name) % FNHSIZE;
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struct fncache *n;
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hlist_for_each_entry(n, &fncache_hash[h], nd) {
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if (!strcmp(n->name, name)) {
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*res = n->res;
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return true;
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}
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}
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return false;
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}
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static void update_fncache(const char *name, bool res)
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{
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struct fncache *n = malloc(sizeof(struct fncache) + strlen(name) + 1);
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int h = shash((const unsigned char *)name) % FNHSIZE;
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if (!n)
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return;
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strcpy(n->name, name);
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n->res = res;
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hlist_add_head(&n->nd, &fncache_hash[h]);
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}
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/* No LRU, only use when bounded in some other way. */
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bool file_available(const char *name)
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{
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bool res;
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if (lookup_fncache(name, &res))
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return res;
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res = access(name, R_OK) == 0;
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update_fncache(name, res);
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return res;
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}
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