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unix: use wq_has_sleeper in unix_dgram_recvmsg 

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>

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Rainer Weikusat 2015-11-26 19:23:15 +00:00 committed by David S. Miller
parent 75c4a57ca9
commit 77b75f4d8c
1 changed files with 4 additions and 2 deletions
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6
net/unix/af_unix.c
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@ -1914,8 +1914,10 @@ 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_wait))
wake_up_interruptible_sync_poll(&u->peer_wait,
POLLOUT | POLLWRNORM |
POLLWRBAND);
if (msg->msg_name)
unix_copy_addr(msg, skb->sk);