* [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode
@ 2019-09-19 9:24 hev
2019-09-20 16:00 ` Jason Baron
0 siblings, 1 reply; 6+ messages in thread
From: hev @ 2019-09-19 9:24 UTC (permalink / raw)
To: linux-fsdevel
Cc: Heiher, Al Viro, Andrew Morton, Davide Libenzi, Davidlohr Bueso,
Dominik Brodowski, Eric Wong, Jason Baron, Linus Torvalds,
Roman Penyaev, Sridhar Samudrala, linux-kernel
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
When s0 fires an event, e1 catches the event, and then e0 catches an event from
e1. After this, There is a thread t0 do epoll_wait() many times on e0, it should
only get one event in total, because e1 is a dded to e0 in edge-triggered mode.
This patch only allows the wakeup(&ep->poll_wait) in ep_scan_ready_list under
two conditions:
1. depth == 0.
2. There have event is added to ep->ovflist during processing.
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 | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index c4159bcc05d9..fa71468dbd51 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -685,6 +685,9 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
if (!ep_locked)
mutex_lock_nested(&ep->mtx, depth);
+ if (!depth || list_empty_careful(&ep->rdllist))
+ pwake++;
+
/*
* Steal the ready list, and re-init the original one to the
* empty list. Also, set ep->ovflist to NULL so that events
@@ -755,7 +758,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
mutex_unlock(&ep->mtx);
/* We have to call this outside the lock */
- if (pwake)
+ if (pwake == 2)
ep_poll_safewake(&ep->poll_wait);
return res;
--
2.23.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode
2019-09-19 9:24 [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode hev
@ 2019-09-20 16:00 ` Jason Baron
2019-09-23 15:33 ` Jason Baron
0 siblings, 1 reply; 6+ messages in thread
From: Jason Baron @ 2019-09-20 16:00 UTC (permalink / raw)
To: hev, linux-fsdevel
Cc: Al Viro, Andrew Morton, Davide Libenzi, Davidlohr Bueso,
Dominik Brodowski, Eric Wong, Linus Torvalds, Roman Penyaev,
Sridhar Samudrala, linux-kernel
On 9/19/19 5:24 AM, 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
>
> When s0 fires an event, e1 catches the event, and then e0 catches an event from
> e1. After this, There is a thread t0 do epoll_wait() many times on e0, it should
> only get one event in total, because e1 is a dded to e0 in edge-triggered mode.
>
> This patch only allows the wakeup(&ep->poll_wait) in ep_scan_ready_list under
> two conditions:
>
> 1. depth == 0.
> 2. There have event is added to ep->ovflist during processing.
>
> 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 | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index c4159bcc05d9..fa71468dbd51 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -685,6 +685,9 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
> if (!ep_locked)
> mutex_lock_nested(&ep->mtx, depth);
>
> + if (!depth || list_empty_careful(&ep->rdllist))
> + pwake++;
> +
> /*
> * Steal the ready list, and re-init the original one to the
> * empty list. Also, set ep->ovflist to NULL so that events
> @@ -755,7 +758,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
> mutex_unlock(&ep->mtx);
>
> /* We have to call this outside the lock */
> - if (pwake)
> + if (pwake == 2)
> ep_poll_safewake(&ep->poll_wait);
>
> return res;
>
Hi,
I was thinking more like the following. I tried it using your test-suite
and it seems to work. What do you think?
Thanks,
-Jason
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index d7f1f50..662136b 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -712,6 +712,15 @@ static __poll_t ep_scan_ready_list(struct eventpoll
*ep,
for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
/*
+ * We only need to wakeup nested epoll fds if
+ * if something has been queued to the overflow list,
+ * since the ep_poll() traverses the rdllist during
+ * recursive poll and thus events on the overflow list
+ * may not be visible yet.
+ */
+ if (!pwake)
+ pwake++;
+ /*
* We need to check if the item is already in the list.
* During the "sproc" callback execution time, items are
* queued into ->ovflist but the "txlist" might already
@@ -755,7 +764,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
mutex_unlock(&ep->mtx);
/* We have to call this outside the lock */
- if (pwake)
+ if (pwake == 2)
ep_poll_safewake(&ep->poll_wait);
return res;
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode
2019-09-20 16:00 ` Jason Baron
@ 2019-09-23 15:33 ` Jason Baron
2019-09-24 14:06 ` Heiher
0 siblings, 1 reply; 6+ messages in thread
From: Jason Baron @ 2019-09-23 15:33 UTC (permalink / raw)
To: hev, linux-fsdevel
Cc: Al Viro, Andrew Morton, Davide Libenzi, Davidlohr Bueso,
Dominik Brodowski, Eric Wong, Linus Torvalds, Roman Penyaev,
Sridhar Samudrala, linux-kernel
On 9/20/19 12:00 PM, Jason Baron wrote:
> On 9/19/19 5:24 AM, 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
>>
>> When s0 fires an event, e1 catches the event, and then e0 catches an event from
>> e1. After this, There is a thread t0 do epoll_wait() many times on e0, it should
>> only get one event in total, because e1 is a dded to e0 in edge-triggered mode.
>>
>> This patch only allows the wakeup(&ep->poll_wait) in ep_scan_ready_list under
>> two conditions:
>>
>> 1. depth == 0.
>> 2. There have event is added to ep->ovflist during processing.
>>
>> 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 | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
>> index c4159bcc05d9..fa71468dbd51 100644
>> --- a/fs/eventpoll.c
>> +++ b/fs/eventpoll.c
>> @@ -685,6 +685,9 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
>> if (!ep_locked)
>> mutex_lock_nested(&ep->mtx, depth);
>>
>> + if (!depth || list_empty_careful(&ep->rdllist))
>> + pwake++;
>> +
>> /*
>> * Steal the ready list, and re-init the original one to the
>> * empty list. Also, set ep->ovflist to NULL so that events
>> @@ -755,7 +758,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
>> mutex_unlock(&ep->mtx);
>>
>> /* We have to call this outside the lock */
>> - if (pwake)
>> + if (pwake == 2)
>> ep_poll_safewake(&ep->poll_wait);
>>
>> return res;
>>
>
>
> Hi,
>
> I was thinking more like the following. I tried it using your test-suite
> and it seems to work. What do you think?
>
> Thanks,
>
> -Jason
>
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index d7f1f50..662136b 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -712,6 +712,15 @@ static __poll_t ep_scan_ready_list(struct eventpoll
> *ep,
> for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
> nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
> /*
> + * We only need to wakeup nested epoll fds if
> + * if something has been queued to the overflow list,
> + * since the ep_poll() traverses the rdllist during
> + * recursive poll and thus events on the overflow list
> + * may not be visible yet.
> + */
> + if (!pwake)
> + pwake++;
> + /*
> * We need to check if the item is already in the list.
> * During the "sproc" callback execution time, items are
> * queued into ->ovflist but the "txlist" might already
> @@ -755,7 +764,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
> mutex_unlock(&ep->mtx);
>
> /* We have to call this outside the lock */
> - if (pwake)
> + if (pwake == 2)
> ep_poll_safewake(&ep->poll_wait);
>
> return res;
>
>
Also, probably better to not have that 'if' in the loop, so how about
the following?
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index d7f1f50..ed0d8da 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -704,12 +704,21 @@ static __poll_t ep_scan_ready_list(struct
eventpoll *ep,
res = (*sproc)(ep, &txlist, priv);
write_lock_irq(&ep->lock);
+ nepi = READ_ONCE(ep->ovflist);
+ /*
+ * We only need to wakeup nested epoll fds if something has been
queued
+ * to the overflow list, since the ep_poll() traverses the rdllist
+ * during recursive poll and thus events on the overflow list
may not be
+ * visible yet.
+ */
+ if (nepi != NULL)
+ pwake++;
/*
* During the time we spent inside the "sproc" callback, some
* other events might have been queued by the poll callback.
* We re-insert them inside the main ready-list here.
*/
- for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
+ for (; (epi = nepi) != NULL;
nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
/*
* We need to check if the item is already in the list.
@@ -755,7 +764,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
mutex_unlock(&ep->mtx);
/* We have to call this outside the lock */
- if (pwake)
+ if (pwake == 2)
ep_poll_safewake(&ep->poll_wait);
return res;
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode
2019-09-23 15:33 ` Jason Baron
@ 2019-09-24 14:06 ` Heiher
2019-09-24 15:18 ` Jason Baron
0 siblings, 1 reply; 6+ messages in thread
From: Heiher @ 2019-09-24 14:06 UTC (permalink / raw)
To: Jason Baron
Cc: linux-fsdevel, Al Viro, Andrew Morton, Davide Libenzi,
Davidlohr Bueso, Dominik Brodowski, Eric Wong, Linus Torvalds,
Roman Penyaev, Sridhar Samudrala, linux-kernel
Hi,
On Mon, Sep 23, 2019 at 11:34 PM Jason Baron <jbaron@akamai.com> wrote:
>
>
>
> On 9/20/19 12:00 PM, Jason Baron wrote:
> > On 9/19/19 5:24 AM, 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
> >>
> >> When s0 fires an event, e1 catches the event, and then e0 catches an event from
> >> e1. After this, There is a thread t0 do epoll_wait() many times on e0, it should
> >> only get one event in total, because e1 is a dded to e0 in edge-triggered mode.
> >>
> >> This patch only allows the wakeup(&ep->poll_wait) in ep_scan_ready_list under
> >> two conditions:
> >>
> >> 1. depth == 0.
> >> 2. There have event is added to ep->ovflist during processing.
> >>
> >> 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 | 5 ++++-
> >> 1 file changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> >> index c4159bcc05d9..fa71468dbd51 100644
> >> --- a/fs/eventpoll.c
> >> +++ b/fs/eventpoll.c
> >> @@ -685,6 +685,9 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
> >> if (!ep_locked)
> >> mutex_lock_nested(&ep->mtx, depth);
> >>
> >> + if (!depth || list_empty_careful(&ep->rdllist))
> >> + pwake++;
> >> +
> >> /*
> >> * Steal the ready list, and re-init the original one to the
> >> * empty list. Also, set ep->ovflist to NULL so that events
> >> @@ -755,7 +758,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
> >> mutex_unlock(&ep->mtx);
> >>
> >> /* We have to call this outside the lock */
> >> - if (pwake)
> >> + if (pwake == 2)
> >> ep_poll_safewake(&ep->poll_wait);
> >>
> >> return res;
> >>
> >
> >
> > Hi,
> >
> > I was thinking more like the following. I tried it using your test-suite
> > and it seems to work. What do you think?
> >
> > Thanks,
> >
> > -Jason
> >
> >
> > diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> > index d7f1f50..662136b 100644
> > --- a/fs/eventpoll.c
> > +++ b/fs/eventpoll.c
> > @@ -712,6 +712,15 @@ static __poll_t ep_scan_ready_list(struct eventpoll
> > *ep,
> > for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
> > nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
> > /*
> > + * We only need to wakeup nested epoll fds if
> > + * if something has been queued to the overflow list,
> > + * since the ep_poll() traverses the rdllist during
> > + * recursive poll and thus events on the overflow list
> > + * may not be visible yet.
> > + */
> > + if (!pwake)
> > + pwake++;
> > + /*
> > * We need to check if the item is already in the list.
> > * During the "sproc" callback execution time, items are
> > * queued into ->ovflist but the "txlist" might already
> > @@ -755,7 +764,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
> > mutex_unlock(&ep->mtx);
> >
> > /* We have to call this outside the lock */
> > - if (pwake)
> > + if (pwake == 2)
> > ep_poll_safewake(&ep->poll_wait);
> >
> > return res;
> >
> >
>
>
> Also, probably better to not have that 'if' in the loop, so how about
> the following?
Hmm. I think this is more accurate.
Thank you.
>
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index d7f1f50..ed0d8da 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -704,12 +704,21 @@ static __poll_t ep_scan_ready_list(struct
> eventpoll *ep,
> res = (*sproc)(ep, &txlist, priv);
>
> write_lock_irq(&ep->lock);
> + nepi = READ_ONCE(ep->ovflist);
> + /*
> + * We only need to wakeup nested epoll fds if something has been
> queued
> + * to the overflow list, since the ep_poll() traverses the rdllist
> + * during recursive poll and thus events on the overflow list
> may not be
> + * visible yet.
> + */
> + if (nepi != NULL)
> + pwake++;
> /*
> * During the time we spent inside the "sproc" callback, some
> * other events might have been queued by the poll callback.
> * We re-insert them inside the main ready-list here.
> */
> - for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
> + for (; (epi = nepi) != NULL;
> nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
> /*
> * We need to check if the item is already in the list.
> @@ -755,7 +764,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
> mutex_unlock(&ep->mtx);
>
> /* We have to call this outside the lock */
> - if (pwake)
> + if (pwake == 2)
> ep_poll_safewake(&ep->poll_wait);
>
> return res;
>
--
Best regards!
Hev
https://hev.cc
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode
2019-09-24 14:06 ` Heiher
@ 2019-09-24 15:18 ` Jason Baron
2019-09-25 1:55 ` Heiher
0 siblings, 1 reply; 6+ messages in thread
From: Jason Baron @ 2019-09-24 15:18 UTC (permalink / raw)
To: Heiher
Cc: linux-fsdevel, Al Viro, Andrew Morton, Davide Libenzi,
Davidlohr Bueso, Dominik Brodowski, Eric Wong, Linus Torvalds,
Roman Penyaev, Sridhar Samudrala, linux-kernel
On 9/24/19 10:06 AM, Heiher wrote:
> Hi,
>
> On Mon, Sep 23, 2019 at 11:34 PM Jason Baron <jbaron@akamai.com> wrote:
>>
>>
>>
>> On 9/20/19 12:00 PM, Jason Baron wrote:
>>> On 9/19/19 5:24 AM, 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
>>>>
>>>> When s0 fires an event, e1 catches the event, and then e0 catches an event from
>>>> e1. After this, There is a thread t0 do epoll_wait() many times on e0, it should
>>>> only get one event in total, because e1 is a dded to e0 in edge-triggered mode.
>>>>
>>>> This patch only allows the wakeup(&ep->poll_wait) in ep_scan_ready_list under
>>>> two conditions:
>>>>
>>>> 1. depth == 0.
What is the point of this condition again? I was thinking we only need
to do #2.
>>>> 2. There have event is added to ep->ovflist during processing.
>>>>
>>>> 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 | 5 ++++-
>>>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
>>>> index c4159bcc05d9..fa71468dbd51 100644
>>>> --- a/fs/eventpoll.c
>>>> +++ b/fs/eventpoll.c
>>>> @@ -685,6 +685,9 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
>>>> if (!ep_locked)
>>>> mutex_lock_nested(&ep->mtx, depth);
>>>>
>>>> + if (!depth || list_empty_careful(&ep->rdllist))
>>>> + pwake++;
>>>> +
This is the check I'm wondering why it's needed?
Thanks,
-Jason
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode
2019-09-24 15:18 ` Jason Baron
@ 2019-09-25 1:55 ` Heiher
0 siblings, 0 replies; 6+ messages in thread
From: Heiher @ 2019-09-25 1:55 UTC (permalink / raw)
To: Jason Baron
Cc: linux-fsdevel, Al Viro, Andrew Morton, Davide Libenzi,
Davidlohr Bueso, Dominik Brodowski, Eric Wong, Linus Torvalds,
Roman Penyaev, Sridhar Samudrala, linux-kernel
Hi,
On Tue, Sep 24, 2019 at 11:19 PM Jason Baron <jbaron@akamai.com> wrote:
>
>
>
> On 9/24/19 10:06 AM, Heiher wrote:
> > Hi,
> >
> > On Mon, Sep 23, 2019 at 11:34 PM Jason Baron <jbaron@akamai.com> wrote:
> >>
> >>
> >>
> >> On 9/20/19 12:00 PM, Jason Baron wrote:
> >>> On 9/19/19 5:24 AM, 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
> >>>>
> >>>> When s0 fires an event, e1 catches the event, and then e0 catches an event from
> >>>> e1. After this, There is a thread t0 do epoll_wait() many times on e0, it should
> >>>> only get one event in total, because e1 is a dded to e0 in edge-triggered mode.
> >>>>
> >>>> This patch only allows the wakeup(&ep->poll_wait) in ep_scan_ready_list under
> >>>> two conditions:
> >>>>
> >>>> 1. depth == 0.
>
>
> What is the point of this condition again? I was thinking we only need
> to do #2.
>
> >>>> 2. There have event is added to ep->ovflist during processing.
> >>>>
> >>>> 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 | 5 ++++-
> >>>> 1 file changed, 4 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> >>>> index c4159bcc05d9..fa71468dbd51 100644
> >>>> --- a/fs/eventpoll.c
> >>>> +++ b/fs/eventpoll.c
> >>>> @@ -685,6 +685,9 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
> >>>> if (!ep_locked)
> >>>> mutex_lock_nested(&ep->mtx, depth);
> >>>>
> >>>> + if (!depth || list_empty_careful(&ep->rdllist))
> >>>> + pwake++;
> >>>> +
>
> This is the check I'm wondering why it's needed?
You are right. This is not needed. Initially, I want to keep the
original behavior of depth 0 for direct poll() in multi-threads.
>
> Thanks,
>
>
> -Jason
>
--
Best regards!
Hev
https://hev.cc
^ permalink raw reply [flat|nested] 6+ messages in thread
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2019-09-19 9:24 [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode hev
2019-09-20 16:00 ` Jason Baron
2019-09-23 15:33 ` Jason Baron
2019-09-24 14:06 ` Heiher
2019-09-24 15:18 ` Jason Baron
2019-09-25 1:55 ` Heiher
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