Messages in this thread Patch in this message | | | From | hev <> | Subject | [PATCH RESEND v5] fs/epoll: Remove unnecessary wakeups of nested epoll | Date | Wed, 9 Oct 2019 14:05:16 +0800 |
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From: Heiher <r@hev.cc>
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-trigger
We 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 <viro@ZenIV.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Davide Libenzi <davidel@xmailserver.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Dominik Brodowski <linux@dominikbrodowski.net> Cc: Eric Wong <e@80x24.org> Cc: Jason Baron <jbaron@akamai.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Roman Penyaev <rpenyaev@suse.de> Cc: Sridhar Samudrala <sridhar.samudrala@intel.com> Cc: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Signed-off-by: hev <r@hev.cc> --- 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; } -- 2.23.0
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