[patch 5/7] epoll keyed wakeups - teach epoll about hints coming with the wakeup key

From: Davide Libenzi
Date: Fri Jan 30 2009 - 22:27:15 EST


The follwing patch uses the events hint now sent by some devices, to
avoid unnecessary wakeups for events that are of no interest for the
caller. This code handles both devices that are sending keyed events,
and the ones that are not (and event the ones that sometimes send events,
and sometimes don't).



Signed-off-by: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>


- Davide


---
fs/eventpoll.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

Index: linux-2.6.mod/fs/eventpoll.c
===================================================================
--- linux-2.6.mod.orig/fs/eventpoll.c 2009-01-30 12:11:39.000000000 -0800
+++ linux-2.6.mod/fs/eventpoll.c 2009-01-30 12:11:47.000000000 -0800
@@ -785,6 +785,15 @@ static int ep_poll_callback(wait_queue_t
if (!(epi->event.events & ~EP_PRIVATE_BITS))
goto out_unlock;

+ /*
+ * Check the events coming with the callback. At this stage, not
+ * every device reports the events in the "key" parameter of the
+ * callback. We need to be able to handle both cases here, hence the
+ * test for "key" != NULL before the event match test.
+ */
+ if (key && !((unsigned long) key & epi->event.events))
+ goto out_unlock;
+
/*
* If we are trasfering events to userspace, we can hold no locks
* (because we're accessing user memory, and because of linux f_op->poll()
@@ -1260,7 +1269,6 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, in
case EPOLL_CTL_ADD:
if (!epi) {
epds.events |= POLLERR | POLLHUP;
-
error = ep_insert(ep, &epds, tfile, fd);
} else
error = -EEXIST;

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