[PATCH] fix ip_gre lockless xmits
From: Willem de Bruijn <willemb@google.com>
Date: 2012-01-26 20:34:42
Tunnel devices set NETIF_F_LLTX to bypass HARD_TX_LOCK. Sit and ipip set this unconditionally in ops->setup, but gre enables it conditionally after parameter passing in ops->newlink. This is not called during tunnel setup as below, however, so GRE tunnels are still taking the lock. modprobe ip_gre ip tunnel add test0 mode gre remote 10.5.1.1 dev lo ip link set test0 up ip addr add 10.6.0.1 dev test0 # cat /sys/class/net/test0/features # $DIR/test_tunnel_xmit 10 10.5.2.1 ip route add 10.5.2.0/24 dev test0 ip tunnel del test0 The newlink callback is only called in rtnl_netlink, and only if the device is new, as it calls register_netdevice internally. Gre tunnels are created at 'ip tunnel add' with ioctl SIOCADDTUNNEL, which calls ipgre_tunnel_locate, which calls register_netdev. rtnl_newlink is called at 'ip link set', but skips ops->newlink and the device is up with locking still enabled. The equivalent ipip tunnel works fine, btw (just substitute 'method gre' for 'method ipip'). On kernels before /sys/class/net/*/features was removed [1], the first commented out line returns 0x6000 with method gre, which indicates that NETIF_F_LLTX (0x1000) is not set. With ipip, it reports 0x7000. This test cannot be used on recent kernels where the sysfs file is removed (and ETHTOOL_GFEATURES does not currently work for tunnel devices, because they lack dev->ethtool_ops). The second commented out line calls a simple transmission test [2] that sends on 24 cores at maximum rate. Results of a single run: ipip: 19,372,306 gre before patch: 4,839,753 gre after patch: 19,133,873 This patch replicates the condition check in ipgre_newlink to ipgre_tunnel_locate. It works for me, both with oseq on and off. This is the first time I looked at rtnetlink and iproute2 code, though, so someone more knowledgeable should probably check the patch. Thanks. The tail of both functions is now identical, by the way. To avoid code duplication, I'll be happy to rework this and merge the two. [1] http://patchwork.ozlabs.org/patch/104610/ [2] http://kernel.googlecode.com/files/xmit_udp_parallel.c Signed-off-by: Willem de Bruijn <willemb@google.com> --- net/ipv4/ip_gre.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 2b53a1f..6b3ca5b 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c@@ -422,6 +422,10 @@ static struct ip_tunnel *ipgre_tunnel_locate(struct net *net, if (register_netdevice(dev) < 0) goto failed_free; + /* Can use a lockless transmit, unless we generate output sequences */ + if (!(nt->parms.o_flags & GRE_SEQ)) + dev->features |= NETIF_F_LLTX; + dev_hold(dev); ipgre_tunnel_link(ign, nt); return nt;
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1.7.7.3