ipv4: Cache local output routes

Commit caacf05e5ad1abf causes big drop of UDP loop back performance.
The cause of the regression is that we do not cache the local output
routes. Each time we send a datagram from unconnected UDP socket,
the kernel allocates a dst_entry and adds it to the rt_uncached_list.
It creates lock contention on the rt_uncached_lock.

Reported-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index e4ba974f143c5dab196bf8671b64be5b155d55cf..fd9ecb52c66bf8815c09e678c452017e9a7e2122 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2028,7 +2028,6 @@ struct rtable *__ip_route_output_key(struct net *net, struct flowi4 *fl4)
                }
                dev_out = net->loopback_dev;
                fl4->flowi4_oif = dev_out->ifindex;
-               res.fi = NULL;
                flags |= RTCF_LOCAL;
                goto make_route;
        }