Commit c722c625 authored Jun 03, 2009 by Herbert Xu Committed by David S. Miller Jun 03, 2009

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent a8c617ea

drivers/net/tun.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -844,12 +844,12 @@ 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);
		}