Arve Hjønnevåg <arve@xxxxxxxxxxx> wrote: > On Mon, Mar 11, 2013 at 5:17 PM, Eric Wong <normalperson@xxxxxxxx> wrote: > > Arve Hjønnevåg <arve@xxxxxxxxxxx> wrote: > >> On Fri, Mar 8, 2013 at 11:10 PM, Eric Wong <normalperson@xxxxxxxx> wrote: > >> > Arve Hjønnevåg <arve@xxxxxxxxxxx> wrote: > >> >> On Fri, Mar 8, 2013 at 12:49 PM, Eric Wong <normalperson@xxxxxxxx> wrote: > >> >> > What happens if ep_modify calls ep_destroy_wakeup_source > >> >> > while __pm_stay_awake is running on the same epi->ws? > >> >> > >> >> Yes, that looks like a problem. I think calling > >> >> ep_destroy_wakeup_source with ep->lock held should fix that. It is not > >> >> clear how useful changing EPOLLWAKEUP in ep_modify is, so > >> >> alternatively we could remove that feature and instead only allow it > >> >> to be set in ep_insert. > >> > > >> > ep->lock would work, but ep->lock is already a source of heavy > >> > contention in my multithreaded+epoll webservers. > >> > >> This should not have any significant impact on that since you would be > >> adding a lock to a code path that is, as far as I know, unused. > >> > >> > Perhaps RCU can be used? I've no experience with RCU, but I've been > >> > meaning to get acquainted with RCU. > >> > >> That adds code to the common path however. The wakeup_source is not > >> touch without holding one of the locks so holding both locks before > >> deleting it seems like a simpler solution. > > > > True. However, I've been looking into eliminating ep->lock in more > > places (maybe entirely)[1]. > > > > I don't think the current overhead of RCU in epoll is significant, > > either. > > > > > > [1] I'll be testing Mathieu's wait-free concurrent queue soon: > > http://mid.gmane.org/20130311213602.GB9829@Krystal > > OK, but is there any way you could use the same locking scheme for the > wakeup_source and the queue? Probably, yes. I think I can just use ep->mtx and ignore the mutex included with wfcq_head, need to protect the rbtree while dequeueing. -- 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
