Arve Hjønnevåg <arve@xxxxxxxxxxx> wrote: > On Thu, Mar 21, 2013 at 8:24 PM, Eric Wong <normalperson@xxxxxxxx> wrote: > > > > With EPOLLET and improper usage (not hitting EAGAIN), the event now > > has a larger window to be lost (as mentioned in my changelog). > > > > What about the case where EPOLLET is not set? The old code did not > drop events in that case. Nothing is dropped, if the event wasn't on the ready list before, ep_poll_callback may still append the ready list while __put_user is running. If the event was on the ready list: 1) It does not matter for EPOLLONESHOT, it'll get masked out and discarded in the next ep_send_events call until ep_modify reenables it. Since ep_modify and ep_send_events both take ep->mtx, there's no conflict. 2) Level Trigger - event stays ready, so nothing is dropped. > > As far as correct __pm_stay_awake/__pm_relax handling, perhaps adding > > an atomic counter to struct eventpoll (or each epitem) will work? > > The wakeup_source should stay in sync with the epoll state. I don't > think any additional state is needed. The problem is epi->state is not set atomically in ep_send_events, Having atomic operations in the loop hurts performance (early versions of this patch did that, and hurt the single-threaded case). Maybe I'll only set epi->state atomically if epi->ws is used... > > 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. > > > > The wakeup_source per epitem is useful for accounting reasons. If > suspend fails, it is useful to know which device caused it. OK. I'll keep epitem->ws -- 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
