Sophie

Sophie

distrib > Scientific%20Linux > 5x > x86_64 > by-pkgid > 27922b4260f65d317aabda37e42bbbff > files > 3196

kernel-2.6.18-238.el5.src.rpm

From: Herbert Xu <herbert.xu@redhat.com>
Date: Thu, 4 Jun 2009 14:51:06 +1000
Subject: [net] tun: only wake up writers
Message-id: 20090604045106.GA24975@gondor.apana.org.au
O-Subject: [RHEL5.4 PATCH] tun: Only wake up writers
Bugzilla: 503191
RH-Acked-by: David Miller <davem@redhat.com>
RH-Acked-by: Rik van Riel <riel@redhat.com>

Hi:

RHEL5 bugzilla 503191

tun: Only wake up writers

When I added socket accounting to tun I inadvertently introduced
spurious wake-up events that kills qemu performance.  The problem
occurs when qemu polls on the tun fd for read, and then transmits
packets.  For each packet transmitted, we will wake up qemu even
if it only cares about read events.

Now this affects all sockets, but it is only a new problem for
tun.  So this patch tries to fix it for tun first and we can then
look at the problem in general.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 3a4afe0..6e66894 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -641,12 +641,12 @@ static void tun_sock_write_space(struct sock *sk)
 	if (!sock_writeable(sk))
 		return;
 
-	if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
-		wake_up_interruptible_sync(sk->sk_sleep);
-
 	if (!test_and_clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags))
 		return;
 
+	if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
+		wake_up_interruptible_sync(sk->sk_sleep);
+
 	tun = container_of(sk, struct tun_sock, sk)->tun;
 	kill_fasync(&tun->fasync, SIGIO, POLL_OUT);
 }