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macvlan: add a salt to mc_hash()

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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: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2013-02-07 16:41:02 +00:00 committed by David S. Miller
parent d527043040
commit 3807ff5899
1 changed files with 13 additions and 4 deletions
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17
drivers/net/macvlan.c
View file

@ -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);
}