netdev - [PATCH net-next v2 2/2] ipv6: Avoid rt6_probe() taking writer lock in the fast path

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Date:	Fri, 24 Jul 2015 09:57:43 -0700
From:	Martin KaFai Lau <kafai@...com>
To:	netdev <netdev@...r.kernel.org>
CC:	Kernel Team <kernel-team@...com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Julian Anastasov <ja@....bg>,
	YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
Subject: [PATCH net-next v2 2/2] ipv6: Avoid rt6_probe() taking writer lock in the fast path

The patch checks neigh->nud_state before acquiring the writer lock.
Note that rt6_probe() is only used in CONFIG_IPV6_ROUTER_PREF.

40 udpflood processes and a /64 gateway route are used.
The gateway has NUD_PERMANENT.  Each of them is run for 30s.
At the end, the total number of finished sendto():

Before: 55M
After: 95M

Signed-off-by: Martin KaFai Lau <kafai@...com>
Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
CC: Julian Anastasov <ja@....bg>
CC: YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
---
 net/ipv6/route.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 6d503db..76dcff8 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -560,6 +560,9 @@ static void rt6_probe(struct rt6_info *rt)
 	rcu_read_lock_bh();
 	neigh = __ipv6_neigh_lookup_noref(rt->dst.dev, &rt->rt6i_gateway);
 	if (neigh) {
+		if (neigh->nud_state & NUD_VALID)
+			goto out;
+
 		work = NULL;
 		write_lock(&neigh->lock);
 		if (!(neigh->nud_state & NUD_VALID) &&
@@ -583,6 +586,7 @@ static void rt6_probe(struct rt6_info *rt)
 		schedule_work(&work->work);
 	}
 
+out:
 	rcu_read_unlock_bh();
 }
 #else
-- 
1.8.1

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