[Qemu-devel] [PATCH 1/7] net: use socket_set_nodelay() for -netdev socket

[Stefan Hajnoczi <stefanha@redhat.com>]

Reduce -netdev socket latency by disabling the Nagle algorithm on
SOCK_STREAM sockets in net/socket.c.  Since we are tunelling Ethernet
over TCP we shouldn't artificially delay outgoing packets, let the guest
decide packet scheduling.

I already get sub-millisecond -netdev socket ping times on localhost, so
there was no measurable difference in my testing.  This won't hurt
though and may improve remote socket performance.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
---
 net/socket.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/socket.c b/net/socket.c
index d8b35a2..b0c83e0 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -438,6 +438,9 @@ static NetSocketState *net_socket_fd_init_stream(NetClientState *peer,
     s->fd = fd;
     s->listen_fd = -1;
 
+    /* Disable Nagle algorithm on TCP sockets to reduce latency */
+    socket_set_nodelay(fd);
+
     if (is_connected) {
         net_socket_connect(s);
     } else {
-- 
1.8.1.4