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ipv6: Avoid rt6_probe() taking writer lock in the fast path

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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>
This commit is contained in:
Martin KaFai Lau 2015-07-24 09:57:43 -07:00 committed by David S. Miller
parent 990edb428c
commit 8d6c31bf57
1 changed files with 4 additions and 0 deletions
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4
net/ipv6/route.c
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@ -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