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neigh: reduce arp latency

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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: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2011-08-09 08:15:58 +00:00 committed by David S. Miller
parent 68c3e5a7b9
commit cd28ca0a3d
1 changed files with 26 additions and 14 deletions
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40
net/core/neighbour.c
View File

@ -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 @@ out:
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);