[PATCH net-next] macvlan: add a salt to mc_hash()

[PATCH net-next] macvlan: add a salt to mc_hash()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

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>
---
Should be applied after 
  "macvlan: broadcast addr should be part of mc_filter"

 drivers/net/macvlan.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index ce7c926..e4b8078 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -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);
 	}

Re: [PATCH net-next] macvlan: add a salt to mc_hash()

[Maciej Żenczykowski]

Signed-off-by: Maciej Żenczykowski <maze@google.com>

On Thu, Feb 7, 2013 at 6:41 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> 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>
> ---
> Should be applied after
>   "macvlan: broadcast addr should be part of mc_filter"
>
>  drivers/net/macvlan.c |   17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
> index ce7c926..e4b8078 100644
> --- a/drivers/net/macvlan.c
> +++ b/drivers/net/macvlan.c
> @@ -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);
>         }
>
>

Re: [PATCH net-next] macvlan: add a salt to mc_hash()

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 07 Feb 2013 18:41:02 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> 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>

Applied.