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>
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 4cda69b..3f0cdc1 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -844,12 +844,12 @@
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);
}