[PATCH] unix: use wq_has_sleeper in unix_dgram_recvmsg

Rainer Weikusat
2015-11-26T19:23:30Z

The current unix_dgram_recvmsg does a wake up for every received
datagram. This seems wasteful as only SOCK_DGRAM client sockets in an
n:1 association with a server socket will ever wait because of the
associated condition. The patch below changes the function such that the
wake up only happens if wq_has_sleeper indicates that someone actually
wants to be notified. Testing with SOCK_SEQPACKET and SOCK_DGRAM socket
seems to confirm that this is an improvment.

Signed-Off-By: Rainer Weikusat <rweikusat@mobileactivedefense.com>
---
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 4e95bdf..7aba73e 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2057,8 +2057,10 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
goto out_unlock;
}

- wake_up_interruptible_sync_poll(&u->peer_wait,
- POLLOUT | POLLWRNORM | POLLWRBAND);
+ if (wq_has_sleeper(&u->peer_wq))
+ wake_up_interruptible_sync_poll(&u->peer_wait,
+ POLLOUT | POLLWRNORM |
+ POLLWRBAND);

if (msg->msg_name)
unix_copy_addr(msg, skb->sk);