On Mon, Sep 23, 2013 at 11:17:39AM -0400, Jason Baron wrote: > 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 > > > I just finished up run some tests over the weekend. The specjbb benchmark went from only scaling 10-12 sockets to scaling to over 32 sockets. I don't have an exact point where it stops scaling but it is under 64 sockets, the size of the machine I had handy. perf seems to indicate the problems are elsewhere, but I will have to rerun and grap some more data. Nate -- 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
