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-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 <[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;
}
--
2.23.0
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-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 <[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
Hi,
On Wed, Oct 9, 2019 at 5:21 PM Roman Penyaev <[email protected]> wrote:
>
> 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-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 <[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
>
>
>
Need to back port this patch to stable branches?
--
Best regards!
Hev
https://hev.cc