Dipankar Sarma a écrit :
On Thu, Sep 15, 2005 at 12:42:03AM +0200, Eric Dumazet wrote:
Dipankar Sarma a écrit :
Not just embedded fdtable, but also the embedded fdsets. I would expect
count, fdt, fdtab and the fdsets to fit into one cache line in
some archs.
But I wonder if 'next_fd' really has to be in 'struct fdtable', maybe it
could be moved to 'struct files_struct' close to file_lock ?
next_fd has to be in struct fdtable. It needs to be consistent
with whichever fdtable a lock-free reader sees.
I may be wrong, but I think a reader never look at next_fd.
next_fd is only used (read/written) by a 'writer', with file_lock hold, in
locate_fd(), copy_fdtable() and get_unused_fd(), __put_unused_fd()
If yes, the whole embedded struct fdtable is readonly.
But not close_on_exec_init or open_fds_init. We would update them
on open/close.
Yes, sure, but those fields are not part of the embedded struct fdtable
Some benchmarking would be useful here.
This simple bench can be used, I got good results on a dual opteron machine.
As Opterons have prety good NUMA links (Hypertransport), I suspect older
hardware should obtain even better results.
$ gcc -O2 -o bench bench.c -lpthread
$ ./bench -t 2 -l 10 # run the bench with 2 threads for 10 seconds.
2 threads, 10 seconds, work_done=1721627
To run it with a small fdset (no more than 3 + (nbthreads) files opened)
$ ./bench -s -t 2 -l 10
2 threads, 10 seconds, work_done=1709716
Unfortunatly I cannot boot the dual opterons at the moment to try to move
next_fd close to file_lock
Eric
/*
* Bench program to exercice multi threads using open()/close()/read()/lseek() calls.
* Usage :
* bench [-t XX] [-l len]
* XX : number of threads
* len : bench time in seconds
* -s : small fdset : try to use embedded sruct fdtable
*/
#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
char *file = "/etc/passwd";
int sflag; /* small fdset */
int end_prog;
unsigned long work_done;
void *perform_work(void *arg)
{
int fd, i;
unsigned long units = 0;
char c;
/* force this program to open more than 64 fds */
if (!sflag)
for (i = 0 ; i < 64 ; i++)
open("/dev/null", O_RDONLY);
while (!end_prog) {
fd = open(file, O_RDONLY);
read(fd, &c, 1);
lseek(fd, 10, SEEK_SET);
read(fd, &c, 1);
lseek(fd, 20, SEEK_SET);
read(fd, &c, 1);
lseek(fd, 30, SEEK_SET);
read(fd, &c, 1);
lseek(fd, 40, SEEK_SET);
read(fd, &c, 1);
close(fd);
units++;
}
pthread_mutex_lock(&mut);
work_done += units;
pthread_mutex_unlock(&mut);
return 0;
}
void usage(int code)
{
fprintf(stderr, "Usage : bench [-s] [-t threads] [-l duration]\n");
exit(code);
}
int main(int argc, char *argv[])
{
int i, c;
int nbthreads = 2;
unsigned int length = 10;
pthread_t *tid;
while ((c = getopt(argc, argv, "st:l:")) != -1) {
if (c == 't')
nbthreads = atoi(optarg);
else if (c == 'l')
length = atoi(optarg);
else if (c == 's')
sflag = 1;
else usage(1);
}
tid = malloc(nbthreads*sizeof(pthread_t));
for (i = 0 ; i < nbthreads; i++)
pthread_create(tid + i, NULL, perform_work, NULL);
sleep(length);
end_prog = 1;
for (i = 0 ; i < nbthreads; i++)
pthread_join(tid[i], NULL);
pthread_mutex_lock(&mut);
printf("%d threads, %u seconds, work_done=%lu\n", nbthreads, length, work_done);
pthread_mutex_unlock(&mut);
return 0;
}
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