On 09/19/2013 12:37 PM, Nathan Zimmer wrote: > On 09/18/2013 02:09 PM, Jason Baron wrote: >> On 09/13/2013 11:54 AM, Nathan Zimmer wrote: >>> We noticed some scaling issue in the SPECjbb benchmark. Running perf >>> we found that the it was spending lots of time in SYS_epoll_ctl. >>> In particular it is holding the epmutex. >>> This patch helps by moving out the kmem_cache_alloc and kmem_cache_free out >>> from under the lock. It improves throughput by around 15% on 16 sockets. >>> >>> While this patch should be fine as it is there are probably is more things >>> that can be done out side the lock, like wakeup_source_unregister, but I am >>> not familar with the area and I don't know of many tests. I did find the >>> one posted by Jason Baron at https://lkml.org/lkml/2011/2/25/297. >>> >>> Any thoughts? >>> >> Hi, >> >> Intersting - I think its also possible to completely drop taking the >> 'epmutex' for EPOLL_CTL_DEL by using rcu, and restricting it on add >> to more 'complex' topologies. That is when we have an epoll descriptor >> that doesn't nest with other epoll descriptors, we don't need the >> global 'epmutex' either. Any chance you can re-run with this? Its a bit >> hacky, but we can clean it up if it makes sense. >> >> Thanks, >> >> -Jason >> > That is working GREAT. It is scaling to 16 jobs quite well. > I will have to grab a larger machine( to see what the new scaling curve > will be. > Cool. Any specific numbers would be helpful for the changelog in support of these changes. Also, I think the move the alloc/free out of from under the locks still might be nice, since we are still taking the per-ep lock in most cases. If you want I can roll those too into a patch series for this when I resubmit. Also, if you're still testing I have a small additional optimization on top of the prior patch: diff --git a/fs/eventpoll.c b/fs/eventpoll.c index d98105d..d967fd7 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -857,7 +857,7 @@ static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait) struct eventpoll *ep = file->private_data; struct readyevents_params params; - params.locked = ((wait->_qproc == ep_ptable_queue_proc) ? 1 : 0); + params.locked = ((wait && (wait->_qproc == ep_ptable_queue_proc)) ? 1 : 0); params.ep = ep; /* Insert inside our poll wait queue */ @@ -1907,7 +1907,6 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, } else list_add(&tf.file->f_tfile_llink, &tfile_check_list); mutex_lock_nested(&ep->mtx, 0); - ep->type = EVENTPOLL_COMPLEX; if (is_file_epoll(tf.file)) { mutex_lock_nested(&(((struct eventpoll *)tf.file->private_data)->mtx), 1); ((struct eventpoll *)tf.file->private_data)->type = EVENTPOLL_COMPLEX; Thanks, -Jason -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
