From 78df76a065ae3b5dbcb9a29912adc02f697de498 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Fri, 24 Aug 2012 05:40:47 +0000
Subject: [PATCH] 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>
---
net/ipv4/route.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 8c8c748ebb280..24fd4c5966431 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);