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SubjectRe: stat benchmark
On Thu, Apr 24, 2008 at 10:59:10PM +0200, Soeren Sandmann wrote:
>
> Under the theory that disk seeks are killing us, one idea is to add a
> 'multistat' system call that would allow statting of many files at a
> time, which would give the disk scheduler more to work with.

Why don't you try this version of your stat-benchmark first? If you
give it the -s option, it will sort the files by inode number first.
I think you will find this should make a significant difference.

If it works, something that would be really great if someone were to
make a generic library which could be used instead of readdir(). I
have something which works as an LD_PRELOAD, but apparently it's been
blowing up on 64-bit systems, and I haven't had time to debug it.
It's probably better to do it as a library which userspace
applications linked against, anyway. Would you or someone you know be
interesed in maybe taking this idea and running with it?

Regards,

- Ted

#include <sys/time.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <dirent.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <getopt.h>

struct dirent_s {
unsigned long long d_ino;
long long d_off;
unsigned short int d_reclen;
unsigned char d_type;
char *d_name;
};

static void
disaster (const char *what)
{
fprintf (stderr, "%s failed: %s\n", what, strerror (errno));
exit (1);
}
static void
dump_caches (void)
{
int fd = open ("/proc/sys/vm/drop_caches", O_RDWR);
if (fd < 0)
disaster ("opening drop_caches");
if (write (fd, "3", strlen ("3")) < 0)
disaster ("writing drop_caches");
if (close (fd) < 0)
disaster ("closing drop_caches");
}
static int ino_cmp(const void *a, const void *b)
{
const struct dirent_s *ds_a = (const struct dirent_s *) a;
const struct dirent_s *ds_b = (const struct dirent_s *) b;
unsigned int i_a, i_b;
i_a = ds_a->d_ino;
i_b = ds_b->d_ino;

return (i_a - i_b);
}
static double
tv_to_sec (const struct timeval *tv)
{
return tv->tv_sec + tv->tv_usec / 1000000.0;
}
static double
time_diff (const struct timeval *before,
const struct timeval *after)
{
return tv_to_sec (after) - tv_to_sec (before);
}
static int
pot (int n)
{
int p = 1;
while (p <= n)
p *= 2;
return p;
}
int
main (int argc, char **argv)
{
DIR *dir = opendir (".");
struct dirent *ent;
struct timeval before;
struct timeval after;
struct dirent_s *ds = NULL;
int n_files;
int do_sort = 0;
int drop_caches = 1;
int i, c;
while ((c = getopt (argc, argv, "sc")) != EOF) {
switch (c) {
case 's':
do_sort++;
break;
case 'c':
drop_caches = 0;
break;
default:
printf("Usage: %s [-s]\n", argv[0]);
}
}
/* Dump caches */
if (drop_caches)
dump_caches();
sleep (1);

/* Read directory */
errno = 0;
gettimeofday (&before, NULL);

n_files = 0;
while ((ent = readdir (dir)))
{
ds = realloc (ds, sizeof (struct dirent_s) * pot (n_files));
if (!ds)
disaster ("realloc");
ds[n_files].d_name = strdup (ent->d_name);
ds[n_files].d_ino = ent->d_ino;
n_files++;
}
if (errno != 0)
disaster ("readdir");
gettimeofday (&after, NULL);

printf ("Time to readdir(): %f s\n", time_diff (&before, &after));

if (do_sort)
qsort(ds, n_files, sizeof(struct dirent_s), ino_cmp);
/* Stat all the files */
gettimeofday (&before, NULL);

for (i = 0; i < n_files; ++i)
{
struct stat statbuf;
stat (ds[i].d_name, &statbuf);
}
gettimeofday (&after, NULL);

printf ("Time to stat %d files: %f s\n",
n_files, time_diff (&before, &after));

return 0;
}/*
* readdir accelerator
*
* (C) Copyright 2003, 2004 by Theodore Ts'o.
*
* Compile using the command:
*
* gcc -o spd_readdir.so -shared spd_readdir.c -ldl
*
* Use it by setting the LD_PRELOAD environment variable:
*
* export LD_PRELOAD=/usr/local/sbin/spd_readdir.so
*
* %Begin-Header%
* This file may be redistributed under the terms of the GNU Public
* License.
* %End-Header%
*
*/
#define ALLOC_STEPSIZE 100
#define MAX_DIRSIZE 0

#define DEBUG

#ifdef DEBUG
#define DEBUG_DIR(x) {if (do_debug) { x; }}
#else
#define DEBUG_DIR(x)
#endif
#define _GNU_SOURCE
#define __USE_LARGEFILE64

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <errno.h>
#include <dlfcn.h>

struct dirent_s {
unsigned long long d_ino;
long long d_off;
unsigned short int d_reclen;
unsigned char d_type;
char *d_name;
};
struct dir_s {
DIR *dir;
int num;
int max;
struct dirent_s *dp;
int pos;
int fd;
struct dirent ret_dir;
struct dirent64 ret_dir64;
};
static int (*real_closedir)(DIR *dir) = 0;
static DIR *(*real_opendir)(const char *name) = 0;
static struct dirent *(*real_readdir)(DIR *dir) = 0;
static struct dirent64 *(*real_readdir64)(DIR *dir) = 0;
static off_t (*real_telldir)(DIR *dir) = 0;
static void (*real_seekdir)(DIR *dir, off_t offset) = 0;
static int (*real_dirfd)(DIR *dir) = 0;
static unsigned long max_dirsize = MAX_DIRSIZE;
static num_open = 0;
#ifdef DEBUG
static int do_debug = 0;
#endif

static void setup_ptr()
{
char *cp;
real_opendir = dlsym(RTLD_NEXT, "opendir");
real_closedir = dlsym(RTLD_NEXT, "closedir");
real_readdir = dlsym(RTLD_NEXT, "readdir");
real_readdir64 = dlsym(RTLD_NEXT, "readdir64");
real_telldir = dlsym(RTLD_NEXT, "telldir");
real_seekdir = dlsym(RTLD_NEXT, "seekdir");
real_dirfd = dlsym(RTLD_NEXT, "dirfd");
if ((cp = getenv("SPD_READDIR_MAX_SIZE")) != NULL) {
max_dirsize = atol(cp);
}
#ifdef DEBUG
if (getenv("SPD_READDIR_DEBUG"))
do_debug++;
#endif
}
static void free_cached_dir(struct dir_s *dirstruct)
{
int i;
if (!dirstruct->dp)
return;
for (i=0; i < dirstruct->num; i++) {
free(dirstruct->dp[i].d_name);
}
free(dirstruct->dp);
dirstruct->dp = 0;
}
static int ino_cmp(const void *a, const void *b)
{
const struct dirent_s *ds_a = (const struct dirent_s *) a;
const struct dirent_s *ds_b = (const struct dirent_s *) b;
ino_t i_a, i_b;
i_a = ds_a->d_ino;
i_b = ds_b->d_ino;

if (ds_a->d_name[0] == '.') {
if (ds_a->d_name[1] == 0)
i_a = 0;
else if ((ds_a->d_name[1] == '.') && (ds_a->d_name[2] == 0))
i_a = 1;
}
if (ds_b->d_name[0] == '.') {
if (ds_b->d_name[1] == 0)
i_b = 0;
else if ((ds_b->d_name[1] == '.') && (ds_b->d_name[2] == 0))
i_b = 1;
}
return (i_a - i_b);
}

DIR *opendir(const char *name)
{
DIR *dir;
struct dir_s *dirstruct;
struct dirent_s *ds, *dnew;
struct dirent64 *d;
struct stat st;
if (!real_opendir)
setup_ptr();
DEBUG_DIR(printf("Opendir(%s) (%d open)\n", name, num_open++));
dir = (*real_opendir)(name);
if (!dir)
return NULL;
dirstruct = malloc(sizeof(struct dir_s));
if (!dirstruct) {
(*real_closedir)(dir);
errno = -ENOMEM;
return NULL;
}
dirstruct->num = 0;
dirstruct->max = 0;
dirstruct->dp = 0;
dirstruct->pos = 0;
dirstruct->dir = 0;
if (max_dirsize && (stat(name, &st) == 0) &&
(st.st_size > max_dirsize)) {
DEBUG_DIR(printf("Directory size %ld, using direct readdir\n",
st.st_size));
dirstruct->dir = dir;
return (DIR *) dirstruct;
}
while ((d = (*real_readdir64)(dir)) != NULL) {
if (dirstruct->num >= dirstruct->max) {
dirstruct->max += ALLOC_STEPSIZE;
DEBUG_DIR(printf("Reallocating to size %d\n",
dirstruct->max));
dnew = realloc(dirstruct->dp,
dirstruct->max * sizeof(struct dir_s));
if (!dnew)
goto nomem;
dirstruct->dp = dnew;
}
ds = &dirstruct->dp[dirstruct->num++];
ds->d_ino = d->d_ino;
ds->d_off = d->d_off;
ds->d_reclen = d->d_reclen;
ds->d_type = d->d_type;
if ((ds->d_name = malloc(strlen(d->d_name)+1)) == NULL) {
dirstruct->num--;
goto nomem;
}
strcpy(ds->d_name, d->d_name);
DEBUG_DIR(printf("readdir: %lu %s\n",
(unsigned long) d->d_ino, d->d_name));
}
dirstruct->fd = dup((*real_dirfd)(dir));
(*real_closedir)(dir);
qsort(dirstruct->dp, dirstruct->num, sizeof(struct dirent_s), ino_cmp);
return ((DIR *) dirstruct);
nomem:
DEBUG_DIR(printf("No memory, backing off to direct readdir\n"));
free_cached_dir(dirstruct);
dirstruct->dir = dir;
return ((DIR *) dirstruct);
}
int closedir(DIR *dir)
{
struct dir_s *dirstruct = (struct dir_s *) dir;
DEBUG_DIR(printf("Closedir (%d open)\n", --num_open));
if (dirstruct->dir)
(*real_closedir)(dirstruct->dir);
if (dirstruct->fd >= 0)
close(dirstruct->fd);
free_cached_dir(dirstruct);
free(dirstruct);
return 0;
}
struct dirent *readdir(DIR *dir)
{
struct dir_s *dirstruct = (struct dir_s *) dir;
struct dirent_s *ds;
if (dirstruct->dir)
return (*real_readdir)(dirstruct->dir);
if (dirstruct->pos >= dirstruct->num)
return NULL;
ds = &dirstruct->dp[dirstruct->pos++];
dirstruct->ret_dir.d_ino = ds->d_ino;
dirstruct->ret_dir.d_off = ds->d_off;
dirstruct->ret_dir.d_reclen = ds->d_reclen;
dirstruct->ret_dir.d_type = ds->d_type;
strncpy(dirstruct->ret_dir.d_name, ds->d_name,
sizeof(dirstruct->ret_dir.d_name));

return (&dirstruct->ret_dir);
}
struct dirent64 *readdir64(DIR *dir)
{
struct dir_s *dirstruct = (struct dir_s *) dir;
struct dirent_s *ds;
if (dirstruct->dir)
return (*real_readdir64)(dirstruct->dir);
if (dirstruct->pos >= dirstruct->num)
return NULL;
ds = &dirstruct->dp[dirstruct->pos++];
dirstruct->ret_dir64.d_ino = ds->d_ino;
dirstruct->ret_dir64.d_off = ds->d_off;
dirstruct->ret_dir64.d_reclen = ds->d_reclen;
dirstruct->ret_dir64.d_type = ds->d_type;
strncpy(dirstruct->ret_dir64.d_name, ds->d_name,
sizeof(dirstruct->ret_dir64.d_name));

return (&dirstruct->ret_dir64);
}
off_t telldir(DIR *dir)
{
struct dir_s *dirstruct = (struct dir_s *) dir;
if (dirstruct->dir)
return (*real_telldir)(dirstruct->dir);
return ((off_t) dirstruct->pos);
}
void seekdir(DIR *dir, off_t offset)
{
struct dir_s *dirstruct = (struct dir_s *) dir;
if (dirstruct->dir) {
(*real_seekdir)(dirstruct->dir, offset);
return;
}
dirstruct->pos = offset;
}
int dirfd(DIR *dir)
{
struct dir_s *dirstruct = (struct dir_s *) dir;
if (dirstruct->dir)
return (*real_dirfd)(dirstruct->dir);
return (dirstruct->fd);
}
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