From: Eric Dumazet <edumazet@google.com>
Date: Fri, 24 Aug 2012 05:40:47 +0000 (+0000)
Subject: ipv4: take rt_uncached_lock only if needed
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=78df76a065ae3b5dbcb9a29912adc02f697de498;p=openwrt%2Fstaging%2Fblogic.git

ipv4: take rt_uncached_lock only if needed

Multicast traffic allocates dst with DST_NOCACHE, but dst is
not inserted into rt_uncached_list.

This slowdown multicast workloads on SMP because rt_uncached_lock is
contended.

Change the test before taking the lock to actually check the dst
was inserted into rt_uncached_list.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 8c8c748ebb28..24fd4c596643 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1263,7 +1263,7 @@ static void ipv4_dst_destroy(struct dst_entry *dst)
 {
 	struct rtable *rt = (struct rtable *) dst;
 
-	if (dst->flags & DST_NOCACHE) {
+	if (!list_empty(&rt->rt_uncached)) {
 		spin_lock_bh(&rt_uncached_lock);
 		list_del(&rt->rt_uncached);
 		spin_unlock_bh(&rt_uncached_lock);