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Commit 3807ff58 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

macvlan: add a salt to mc_hash() 



Some multicast addresses are common to all macvlans,
so if a multicast message has a hash value collision, we
have to deliver a copy to all macvlans, adding significant
latency and possible packet drops if netdev_max_backlog
limit is hit.

Having a per macvlan hash function permits to reduce the
impact of hash collisions.

Suggested-by: default avatarMaciej Żenczykowski <maze@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarMaciej Żenczykowski <maze@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d5270430

drivers/net/macvlan.c

+13 −4
Original line number Diff line number Diff line
@@ -127,10 +127,18 @@ static int macvlan_broadcast_one(struct sk_buff *skb, 
	return vlan->receive(skb);

}



static unsigned int mc_hash(const unsigned char *addr)

static u32 macvlan_hash_mix(const struct macvlan_dev *vlan)

{

	return (u32)(((unsigned long)vlan) >> L1_CACHE_SHIFT);

}





static unsigned int mc_hash(const struct macvlan_dev *vlan,

			    const unsigned char *addr)

{

	u32 val = __get_unaligned_cpu32(addr + 2);



	val ^= macvlan_hash_mix(vlan);

	return hash_32(val, MACVLAN_MC_FILTER_BITS);

}
@@ -145,7 +153,7 @@ static void macvlan_broadcast(struct sk_buff *skb, 
	struct sk_buff *nskb;

	unsigned int i;

	int err;

	unsigned int hash = mc_hash(eth->h_dest);

	unsigned int hash;



	if (skb->protocol == htons(ETH_P_PAUSE))

		return;
@@ -155,6 +163,7 @@ static void macvlan_broadcast(struct sk_buff *skb, 
			if (vlan->dev == src || !(vlan->mode & mode))

				continue;



			hash = mc_hash(vlan, eth->h_dest);

			if (!test_bit(hash, vlan->mc_filter))

				continue;

			nskb = skb_clone(skb, GFP_ATOMIC);
@@ -424,10 +433,10 @@ static void macvlan_set_mac_lists(struct net_device *dev) 


		bitmap_zero(filter, MACVLAN_MC_FILTER_SZ);

		netdev_for_each_mc_addr(ha, dev) {

			__set_bit(mc_hash(ha->addr), filter);

			__set_bit(mc_hash(vlan, ha->addr), filter);

		}



		__set_bit(mc_hash(dev->broadcast), filter);

		__set_bit(mc_hash(vlan, dev->broadcast), filter);



		bitmap_copy(vlan->mc_filter, filter, MACVLAN_MC_FILTER_SZ);

	}