On 2019-10-09 08:05, hev wrote:
From: Heiher <[email protected]>Take the case where we have: t0 | (ew) e0 | (et) e1 | (lt) s0 t0: thread 0 e0: epoll fd 0 e1: epoll fd 1 s0: socket fd 0 ew: epoll_wait et: edge-trigger lt: level-triggerWe remove unnecessary wakeups to prevent the nested epoll that working in edge-triggered mode to waking up continuously. Test code: #include <unistd.h> #include <sys/epoll.h> #include <sys/socket.h> int main(int argc, char *argv[]) { int sfd[2]; int efd[2]; struct epoll_event e; if (socketpair(AF_UNIX, SOCK_STREAM, 0, sfd) < 0) goto out; efd[0] = epoll_create(1); if (efd[0] < 0) goto out; efd[1] = epoll_create(1); if (efd[1] < 0) goto out; e.events = EPOLLIN; if (epoll_ctl(efd[1], EPOLL_CTL_ADD, sfd[0], &e) < 0) goto out; e.events = EPOLLIN | EPOLLET; if (epoll_ctl(efd[0], EPOLL_CTL_ADD, efd[1], &e) < 0) goto out; if (write(sfd[1], "w", 1) != 1) goto out; if (epoll_wait(efd[0], &e, 1, 0) != 1) goto out; if (epoll_wait(efd[0], &e, 1, 0) != 0) goto out; close(efd[0]); close(efd[1]); close(sfd[0]); close(sfd[1]); return 0; out: return -1; } More tests: https://github.com/heiher/epoll-wakeup Cc: Al Viro <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Davide Libenzi <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: Dominik Brodowski <[email protected]> Cc: Eric Wong <[email protected]> Cc: Jason Baron <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Roman Penyaev <[email protected]> Cc: Sridhar Samudrala <[email protected]> Cc: [email protected] Cc: [email protected] Signed-off-by: hev <[email protected]> --- fs/eventpoll.c | 16 ---------------- 1 file changed, 16 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index c4159bcc05d9..75fccae100b5 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c@@ -671,7 +671,6 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,void *priv, int depth, bool ep_locked) { __poll_t res; - int pwake = 0; struct epitem *epi, *nepi; LIST_HEAD(txlist);@@ -738,26 +737,11 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,*/ list_splice(&txlist, &ep->rdllist); __pm_relax(ep->ws); - - if (!list_empty(&ep->rdllist)) { - /* - * Wake up (if active) both the eventpoll wait list and - * the ->poll() wait list (delayed after we release the lock). - */ - if (waitqueue_active(&ep->wq)) - wake_up(&ep->wq); - if (waitqueue_active(&ep->poll_wait)) - pwake++; - } write_unlock_irq(&ep->lock); if (!ep_locked) mutex_unlock(&ep->mtx); - /* We have to call this outside the lock */ - if (pwake) - ep_poll_safewake(&ep->poll_wait); - return res; }
This looks good to me. Heiher, mind to make kselftest out of your test suite?
Reviewed-by: Roman Penyaev <[email protected]> -- Roman
