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Commit cd28ca0a authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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neigh: reduce arp latency 



Remove the artificial HZ latency on arp resolution.

Instead of firing a timer in one jiffy (up to 10 ms if HZ=100), lets
send the ARP message immediately.

Before patch :

# arp -d 192.168.20.108 ; ping -c 3 192.168.20.108
PING 192.168.20.108 (192.168.20.108) 56(84) bytes of data.
64 bytes from 192.168.20.108: icmp_seq=1 ttl=64 time=9.91 ms
64 bytes from 192.168.20.108: icmp_seq=2 ttl=64 time=0.065 ms
64 bytes from 192.168.20.108: icmp_seq=3 ttl=64 time=0.061 ms

After patch :

$ arp -d 192.168.20.108 ; ping -c 3 192.168.20.108
PING 192.168.20.108 (192.168.20.108) 56(84) bytes of data.
64 bytes from 192.168.20.108: icmp_seq=1 ttl=64 time=0.152 ms
64 bytes from 192.168.20.108: icmp_seq=2 ttl=64 time=0.064 ms
64 bytes from 192.168.20.108: icmp_seq=3 ttl=64 time=0.074 ms

Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 68c3e5a7

net/core/neighbour.c

+26 −14
Original line number Original line Diff line number Diff line
@@ -844,6 +844,19 @@ static void neigh_invalidate(struct neighbour *neigh) 
	skb_queue_purge(&neigh->arp_queue);

	skb_queue_purge(&neigh->arp_queue);

}

}





static void neigh_probe(struct neighbour *neigh)

	__releases(neigh->lock)

{

	struct sk_buff *skb = skb_peek(&neigh->arp_queue);

	/* keep skb alive even if arp_queue overflows */

	if (skb)

		skb = skb_copy(skb, GFP_ATOMIC);

	write_unlock(&neigh->lock);

	neigh->ops->solicit(neigh, skb);

	atomic_inc(&neigh->probes);

	kfree_skb(skb);

}



/* Called when a timer expires for a neighbour entry. */

/* Called when a timer expires for a neighbour entry. */





static void neigh_timer_handler(unsigned long arg)

static void neigh_timer_handler(unsigned long arg)
@@ -920,14 +933,7 @@ static void neigh_timer_handler(unsigned long arg) 
			neigh_hold(neigh);

			neigh_hold(neigh);

	}

	}

	if (neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) {

	if (neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) {

		struct sk_buff *skb = skb_peek(&neigh->arp_queue);

		neigh_probe(neigh);

		/* keep skb alive even if arp_queue overflows */

		if (skb)

			skb = skb_copy(skb, GFP_ATOMIC);

		write_unlock(&neigh->lock);

		neigh->ops->solicit(neigh, skb);

		atomic_inc(&neigh->probes);

		kfree_skb(skb);

	} else {

	} else {

out:

out:

		write_unlock(&neigh->lock);

		write_unlock(&neigh->lock);
@@ -942,7 +948,7 @@ static void neigh_timer_handler(unsigned long arg) 
int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)

int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)

{

{

	int rc;

	int rc;

	unsigned long now;

	bool immediate_probe = false;





	write_lock_bh(&neigh->lock);

	write_lock_bh(&neigh->lock);
@@ -950,14 +956,16 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb) 
	if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))

	if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))

		goto out_unlock_bh;

		goto out_unlock_bh;





	now = jiffies;



	if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) {

	if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) {

		if (neigh->parms->mcast_probes + neigh->parms->app_probes) {

		if (neigh->parms->mcast_probes + neigh->parms->app_probes) {

			unsigned long next, now = jiffies;



			atomic_set(&neigh->probes, neigh->parms->ucast_probes);

			atomic_set(&neigh->probes, neigh->parms->ucast_probes);

			neigh->nud_state     = NUD_INCOMPLETE;

			neigh->nud_state     = NUD_INCOMPLETE;

			neigh->updated = jiffies;

			neigh->updated = now;

			neigh_add_timer(neigh, now + 1);

			next = now + max(neigh->parms->retrans_time, HZ/2);

			neigh_add_timer(neigh, next);

			immediate_probe = true;

		} else {

		} else {

			neigh->nud_state = NUD_FAILED;

			neigh->nud_state = NUD_FAILED;

			neigh->updated = jiffies;

			neigh->updated = jiffies;
@@ -989,7 +997,11 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb) 
		rc = 1;

		rc = 1;

	}

	}

out_unlock_bh:

out_unlock_bh:

	write_unlock_bh(&neigh->lock);

	if (immediate_probe)

		neigh_probe(neigh);

	else

		write_unlock(&neigh->lock);

	local_bh_enable();

	return rc;

	return rc;

}

}

EXPORT_SYMBOL(__neigh_event_send);

EXPORT_SYMBOL(__neigh_event_send);