Arve Hjønnevåg <arve@xxxxxxxxxxx> wrote: > On Thu, Mar 21, 2013 at 4:52 AM, Eric Wong <normalperson@xxxxxxxx> wrote: > > Changes since v2: > > * epi->state is no longer atomic, we only cmpxchg in ep_poll_callback > > now and rely on implicit barriers in other places for reading. > > * intermediate EP_STATE_DEQUEUE removed, this (with xchg) caused too > > much overhead in the ep_send_events loop and could not eliminate > > starvation dangers from improper EPOLLET usage (the original code > > had this problem, too, the window is just a few cycles larger, now). > > * minor code cleanups > > /* > > * Activate ep->ws before deactivating epi->ws to prevent > > Does anything deactivate ep->ws now? Oops, I left that out when I killed ep_scan_ready_list. But I think we need a different approach to wakeup sources in this series... > > + /* > > + * reset item state for EPOLLONESHOT and EPOLLET > > + * no barrier here, rely on ep->mtx release for write barrier > > + */ > > What happens if ep_poll_callback runs before you set epi->state below? > It used to queue on ep->ovflist and call __pm_stay_awake on ep->ws, > but now it does not appear to do anything. > > > + epi->state = EP_STATE_IDLE; > > } > > > > return eventcnt; > > } > > With EPOLLET and improper usage (not hitting EAGAIN), the event now has a larger window to be lost (as mentioned in my changelog). As far as correct __pm_stay_awake/__pm_relax handling, perhaps adding an atomic counter to struct eventpoll (or each epitem) will work? If we go with atomic counter in struct eventpoll, is per-epitem wakeup_source still necessary? We have space in epitem now, but maybe one day we will might need it. Thanks for looking at this patch. Btw, I'm curious; which applications use EPOLLWAKEUP? My epoll work is focused on network servers with thousands of clients, and I don't think any of them use (or have use for) EPOLLWAKEUP. But I will keep EPOLLWAKEUP users in mind when working on epoll :) -- 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
