Hi,
If multiple threads are parked on epoll_wait (on a single epoll fd) and
events become available, epoll performs a wake up of all threads of the
poll wait list, causing a thundering herd of processes trying to grab
the eventpoll lock.
This patch addresses this by using exclusive waiters (wake one). Once
the exclusive thread finishes transferring it's events, a new thread
is woken if there are more events available.
Makes sense?
Signed-off-by: Davi E. M. Arnaut <[EMAIL PROTECTED]>
---
fs/eventpoll.c | 7 +++++++
1 file changed, 7 insertions(+)
Index: linux-2.6/fs/eventpoll.c
===================================================================
--- linux-2.6.orig/fs/eventpoll.c
+++ linux-2.6/fs/eventpoll.c
@@ -1491,6 +1491,12 @@ static void ep_reinject_items(struct eve
}
}
+ /*
+ * If there is events available, wake up the next waiter, if any.
+ */
+ if (!ricnt)
+ ricnt = !list_empty(&ep->rdllist);
+
if (ricnt) {
/*
* Wake up ( if active ) both the eventpoll wait list and the
->poll()
@@ -1570,6 +1576,7 @@ retry:
* ep_poll_callback() when events will become available.
*/
init_waitqueue_entry(&wait, current);
+ wait.flags |= WQ_FLAG_EXCLUSIVE;
__add_wait_queue(&ep->wq, &wait);
for (;;) {
--
-
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