[AF_UNIX]: Remove superfluous reference counting in unix_stream_sendmsg (830a1e5c) · Commits · 戴 / test

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:

Benjamin LaHaise <benjamin.c.lahaise@intel.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/unix/af_unix.c

+5 −6

Original line number	Diff line number	Diff line
		@@ -1063,10 +1063,12 @@ restart:
		/* Set credentials */
		sk->sk_peercred = other->sk_peercred;

		sock_hold(newsk);
		unix_peer(sk) = newsk;
		sock->state = SS_CONNECTED;
		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);

		@@ -1414,7 +1416,7 @@ static int unix_stream_sendmsg(struct kiocb kiocb, struct socket sock,
		} else {
		sunaddr = NULL;
		err = -ENOTCONN;
		other = unix_peer_get(sk);
		other = unix_peer(sk);
		if (!other)
		goto out_err;
		}
		@@ -1476,7 +1478,6 @@ static int unix_stream_sendmsg(struct kiocb kiocb, struct socket sock,
		other->sk_data_ready(other, size);
		sent+=size;
		}
		sock_put(other);

		scm_destroy(siocb->scm);
		siocb->scm = NULL;
		@@ -1491,8 +1492,6 @@ pipe_err:
		send_sig(SIGPIPE,current,0);
		err = -EPIPE;
		out_err:
		if (other)
		sock_put(other);
		scm_destroy(siocb->scm);
		siocb->scm = NULL;
		return sent ? : err;

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