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@fb.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
CC: Julian Anastasov <ja@ssi.bg>
CC: YOSHIFUJI Hideaki <hideaki.yoshifuji@miraclelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 0ef5262..54fccf0 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -560,6 +560,9 @@
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 @@
schedule_work(&work->work);
}
+out:
rcu_read_unlock_bh();
}
#else