Re: ext2 performance in 2.5.25 versus 2.4.19pre8aa2

[Lincoln Dale]

At 11:49 AM 15/07/2002 +0200, Andrea Arcangeli wrote:
> > my test app uses pthreads (one thread per disk-worker) and
> > pthread_cond_wait in the master task to wait for all workers to finish.
> > i'll switch the app to use clone() and sys_futex instead.
>
>unless you call pthread routines during the workload, pthreads cannot be
>the reason for a slowdown.

the test app does:

(parent)
         for (i=0; i < num_devices; i++) {
                 err = pthread_create(&(device[i]->thread), NULL,  (void 
*)run_tests, (void *) i);
                 ..
         }

         /* wait for all threads to exit */
         while (active_threads != 0) {
                 pthread_mutex_lock(&sync_thread_mutex);

                 gettimeofday(&now, NULL);
                 timeout.tv_sec = now.tv_sec + 5;
                 timeout.tv_nsec = now.tv_usec * 1000;
                 retcode = 0;

                 while ((active_threads != 0) && (retcode != ETIMEDOUT)) {
                         retcode = 
pthread_cond_timedwait(&sync_thread_cond, &sync_thread_mutex, &timeout);
                 }

                 if (retcode == ETIMEDOUT) {
                         print_status_update();
                 }
                 pthread_mutex_unlock(&sync_thread_mutex);
         }

(each worker, when it finishes)
         pthread_mutex_lock(&sync_thread_mutex);
         active_threads--;
         pthread_cond_broadcast(&sync_thread_cond);
         pthread_mutex_unlock(&sync_thread_mutex);
         pthread_exit(0);

no idea what the pthread_cond_timedwait does under the covers, but i bet 
its bad..

>BTW, Lincol, I still have a pending answer for you, about the mmap
>slowdown, that's because of reduced readahead mostly, you can tune it
>with page-cluster sysctl, it's not only because of the expensive page
>faults that mmap I/O implies. I've some revolutionary idea about
>replacing readahead, not that it matters for your workload that is
>reading physically contigous though.

i only added the mmap() for interests-sake; the intent of my benchmarking 
was less-so to stress linux, more-so to stress some storage-networking 
plumbing (iSCSI & FC stuff), but its been an interesting series of 
experiments nontheless.

cheers,

lincoln.