af_unix: optimize unix_dgram_poll()
unix_dgram_poll() is pretty expensive to check POLLOUT status, because
it has to lock the socket to get its peer, take a reference on the peer
to check its receive queue status, and queue another poll_wait on
peer_wait. This all can be avoided if the process calling
unix_dgram_poll() is not interested in POLLOUT status. It makes
unix_dgram_recvmsg() faster by not queueing irrelevant pollers in
peer_wait.
On a test program provided by Alan Crequy :
Before:
real 0m0.211s
user 0m0.000s
sys 0m0.208s
After:
real 0m0.044s
user 0m0.000s
sys 0m0.040s
Suggested-by: Davide Libenzi <davidel@xmailserver.org>
Reported-by: Alban Crequy <alban.crequy@collabora.co.uk>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e889875..7ff31c6 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2091,6 +2091,10 @@
return mask;
}
+ /* No write status requested, avoid expensive OUT tests. */
+ if (wait && !(wait->key & (POLLWRBAND | POLLWRNORM | POLLOUT)))
+ return mask;
+
writable = unix_writable(sk);
other = unix_peer_get(sk);
if (other) {