| Message ID | 20191009060516.3577-1-r@hev.cc (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RESEND,v5] fs/epoll: Remove unnecessary wakeups of nested epoll | expand |
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
Hi, On Wed, Oct 9, 2019 at 5:21 PM Roman Penyaev <rpenyaev@suse.de> wrote: > > 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 > > > Need to back port this patch to stable branches?
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; }