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Commit 830a1e5c authored by Benjamin LaHaise's avatar Benjamin LaHaise Committed by David S. Miller
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[AF_UNIX]: Remove superfluous reference counting in unix_stream_sendmsg 



AF_UNIX stream socket performance on P4 CPUs tends to suffer due to a
lot of pipeline flushes from atomic operations.  The patch below
removes the sock_hold() and sock_put() in unix_stream_sendmsg().  This
should be safe as the socket still holds a reference to its peer which
is only released after the file descriptor's final user invokes
unix_release_sock().  The only consideration is that we must add a
memory barrier before setting the peer initially.

Signed-off-by: default avatarBenjamin LaHaise <benjamin.c.lahaise@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c1cbe4b7

net/unix/af_unix.c

+5 −6
Original line number Original line Diff line number Diff line
@@ -1063,10 +1063,12 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr, 
	/* Set credentials */

	/* Set credentials */

	sk->sk_peercred = other->sk_peercred;

	sk->sk_peercred = other->sk_peercred;





	sock_hold(newsk);

	unix_peer(sk)	= newsk;

	sock->state	= SS_CONNECTED;

	sock->state	= SS_CONNECTED;

	sk->sk_state	= TCP_ESTABLISHED;

	sk->sk_state	= TCP_ESTABLISHED;

	sock_hold(newsk);



	smp_mb__after_atomic_inc();	/* sock_hold() does an atomic_inc() */

	unix_peer(sk)	= newsk;





	unix_state_wunlock(sk);

	unix_state_wunlock(sk);
@@ -1414,7 +1416,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock, 
	} else {

	} else {

		sunaddr = NULL;

		sunaddr = NULL;

		err = -ENOTCONN;

		err = -ENOTCONN;

		other = unix_peer_get(sk);

		other = unix_peer(sk);

		if (!other)

		if (!other)

			goto out_err;

			goto out_err;

	}

	}
@@ -1476,7 +1478,6 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock, 
		other->sk_data_ready(other, size);

		other->sk_data_ready(other, size);

		sent+=size;

		sent+=size;

	}

	}

	sock_put(other);





	scm_destroy(siocb->scm);

	scm_destroy(siocb->scm);

	siocb->scm = NULL;

	siocb->scm = NULL;
@@ -1491,8 +1492,6 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock, 
		send_sig(SIGPIPE,current,0);

		send_sig(SIGPIPE,current,0);

	err = -EPIPE;

	err = -EPIPE;

out_err:

out_err:

        if (other)

		sock_put(other);

	scm_destroy(siocb->scm);

	scm_destroy(siocb->scm);

	siocb->scm = NULL;

	siocb->scm = NULL;

	return sent ? : err;

	return sent ? : err;