lkml.org 
[lkml]   [2019]   [Oct]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RESEND v5] fs/epoll: Remove unnecessary wakeups of nested epoll
On 2019-10-09 08:05, hev wrote:
> 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;
> }

This looks good to me. Heiher, mind to make kselftest out of your test
suite?

Reviewed-by: Roman Penyaev <rpenyaev@suse.de>

--
Roman



\
 
 \ /
  Last update: 2019-10-09 11:21    [W:0.041 / U:0.872 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site