epoll: optimize setting task running after blocking

Davidlohr Bueso · torvalds · commit 4d5755b14766 · 2015-02-13T21:21:40.000-08:00
After waking up a task waiting for an event, we explicitly mark it as
TASK_RUNNING (which is necessary as we do the checks for wakeups as
TASK_INTERRUPTIBLE).  Once running and dealing with actually delivering
the events, we're obviously not planning on calling schedule, thus we can
relax the implied barrier and simply update the state with
__set_current_state().

Signed-off-by: Davidlohr Bueso &lt;dbueso@suse.de&gt;
Cc: Alexander Viro &lt;viro@zeniv.linux.org.uk&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
@@ -1639,9 +1639,9 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
 
 			spin_lock_irqsave(&ep->lock, flags);
 		}
-		__remove_wait_queue(&ep->wq, &wait);
 
-		set_current_state(TASK_RUNNING);
+		__remove_wait_queue(&ep->wq, &wait);
+		__set_current_state(TASK_RUNNING);
 	}
 check_events:
 	/* Is it worth to try to dig for events ? */

Original file line number	Diff line number	Diff line change
`@@ -1639,9 +1639,9 @@ static int ep_poll(struct eventpoll ep, struct epoll_event __user events,`
`1639`	`1639`
`1640`	`1640`	`spin_lock_irqsave(&ep->lock, flags);`
`1641`	`1641`	`}`
`1642`		`- __remove_wait_queue(&ep->wq, &wait);`
`1643`	`1642`
`1644`		`- set_current_state(TASK_RUNNING);`
	`1643`	`+ __remove_wait_queue(&ep->wq, &wait);`
	`1644`	`+ __set_current_state(TASK_RUNNING);`
`1645`	`1645`	`}`
`1646`	`1646`	`check_events:`
`1647`	`1647`	`/* Is it worth to try to dig for events ? */`