netlink-socket: Increase Netlink socket receive buffer size.

Open vSwitch userspace can set up flows at a high rate, but it is somewhat
"bursty" in opportunities to set up flows, by which I mean that OVS sets up
a batch of flows, then goes off and does some other work for a while, then
sets up another batch of flows, and so on.  The result is that, if a large
number of packets that need flow setups come in all at once, then some of
them can overflow the relatively small kernel-to-user buffers.

This commit increases the kernel-to-user buffers from the default of
approximately 120 kB each to 1 MB each.  In one somewhat synthetic test
case that I ran based on an "hping3" that generated a load of about 20,000
new flows per second (including both requests and replies), this reduced
the packets dropped at the kernel-to-user interface from about 30% to none.
I expect that it will similarly improve packet loss in workloads where
flow arrival is not easily predictable.

(This has little effect on workloads generated by "ovs-benchmark rate"
because that benchmark is effectively "self-clocking", that is, a new flow
is triggered only by a reply to a request made earlier, which means that
the number of buffered packets at any given has a known, constant upper
limit.)

Bug #10210.
Signed-off-by: Ben Pfaff <blp@nicira.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/lib/netlink-socket.c b/lib/netlink-socket.c
index bc462353..df6f1d8b 100644
--- a/lib/netlink-socket.c
+++ b/lib/netlink-socket.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -89,6 +89,7 @@ nl_sock_create(int protocol, struct nl_sock **sockp)
     struct nl_sock *sock;
     struct sockaddr_nl local, remote;
     socklen_t local_size;
+    int rcvbuf;
     int retval = 0;
 
     if (!max_iovs) {
@@ -122,6 +123,13 @@ nl_sock_create(int protocol, struct nl_sock **sockp)
     sock->protocol = protocol;
     sock->dump = NULL;
 
+    rcvbuf = 1024 * 1024;
+    if (setsockopt(sock->fd, SOL_SOCKET, SO_RCVBUFFORCE,
+                   &rcvbuf, sizeof rcvbuf)) {
+        VLOG_WARN_RL(&rl, "setting %d-byte socket receive buffer failed (%s)",
+                     rcvbuf, strerror(errno));
+    }
+
     retval = get_socket_rcvbuf(sock->fd);
     if (retval < 0) {
         retval = -retval;