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authorDavidlohr Bueso <dave@stgolabs.net>2019-01-03 23:27:26 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2019-01-04 21:13:46 (GMT)
commit86c051793b4c941ee4481725d57cf2a27f6b3aaf (patch)
treef971e2b0f3dd64fd2fb6f46707c10cdf549de09d /fs
parent35cff1a6e0236500584a8ae227fe08120d9b5ee2 (diff)
fs/epoll: deal with wait_queue only once
There is no reason why we rearm the waitiqueue upon every fetch_events retry (for when events are found yet send_events() fails). If nothing else, this saves four lock operations per retry, and furthermore reduces the scope of the lock even further. [akpm@linux-foundation.org: restore code to original position, fix and reflow comment] Link: http://lkml.kernel.org/r/20181114182532.27981-2-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Jason Baron <jbaron@akamai.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/eventpoll.c29
1 files changed, 18 insertions, 11 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 752dbc4..2329f96 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1749,6 +1749,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
{
int res = 0, eavail, timed_out = 0;
u64 slack = 0;
+ bool waiter = false;
wait_queue_entry_t wait;
ktime_t expires, *to = NULL;
@@ -1794,14 +1795,18 @@ fetch_events:
ep_reset_busy_poll_napi_id(ep);
/*
- * We don't have any available event to return to the caller.
- * We need to sleep here, and we will be wake up by
- * ep_poll_callback() when events will become available.
+ * We don't have any available event to return to the caller. We need
+ * to sleep here, and we will be woken by ep_poll_callback() when events
+ * become available.
*/
- init_waitqueue_entry(&wait, current);
- spin_lock_irq(&ep->wq.lock);
- __add_wait_queue_exclusive(&ep->wq, &wait);
- spin_unlock_irq(&ep->wq.lock);
+ if (!waiter) {
+ waiter = true;
+ init_waitqueue_entry(&wait, current);
+
+ spin_lock_irq(&ep->wq.lock);
+ __add_wait_queue_exclusive(&ep->wq, &wait);
+ spin_unlock_irq(&ep->wq.lock);
+ }
for (;;) {
/*
@@ -1837,10 +1842,6 @@ fetch_events:
__set_current_state(TASK_RUNNING);
- spin_lock_irq(&ep->wq.lock);
- __remove_wait_queue(&ep->wq, &wait);
- spin_unlock_irq(&ep->wq.lock);
-
send_events:
/*
* Try to transfer events to user space. In case we get 0 events and
@@ -1851,6 +1852,12 @@ send_events:
!(res = ep_send_events(ep, events, maxevents)) && !timed_out)
goto fetch_events;
+ if (waiter) {
+ spin_lock_irq(&ep->wq.lock);
+ __remove_wait_queue(&ep->wq, &wait);
+ spin_unlock_irq(&ep->wq.lock);
+ }
+
return res;
}

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