netdev - Re: [PATCH V3 2/2] bonding support for IPv6 transmit hashing

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Date:	Sun, 1 Jul 2012 05:57:57 +0200
From:	Hannes Frederic Sowa <hannes@...lcolloid.de>
To:	John <linux@...2.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH V3 2/2] bonding support for IPv6 transmit hashing

On Sat, Jun 30, 2012 at 9:38 PM, John <linux@...2.net> wrote:
> On 6/30/2012 4:59 AM, Hannes Frederic Sowa wrote:
>> On Sat, Jun 30, 2012 at 8:17 AM, John <linux@...2.net> wrote:
>>>
>>> diff --git a/Documentation/networking/bonding.txt
>>> b/Documentation/networking/bonding.txt
>>> index bfea8a3..5db14fe 100644
>>> --- a/Documentation/networking/bonding.txt
>>> +++ b/Documentation/networking/bonding.txt
>>> @@ -752,12 +752,22 @@ xmit_hash_policy
>>>                  protocol information to generate the hash.
>>>
>>>                  Uses XOR of hardware MAC addresses and IP addresses to
>>> -               generate the hash.  The formula is
>>> +               generate the hash.  The IPv4 formula is
>>>
>>>                  (((source IP XOR dest IP) AND 0xffff) XOR
>>>                          ( source MAC XOR destination MAC ))
>>>                                  modulo slave count
>>>
>>> +               The IPv6 forumla is
>>> +
>>> +               iphash =
>>> +                       (source ip quad 2 XOR dest IP quad 2) XOR
>>> +                       (source ip quad 3 XOR dest IP quad 3) XOR
>>> +                       (source ip quad 4 XOR dest IP quad 4)
>>> +
>>> +               ((iphash >> 16) XOR (iphash >> 8) XOR iphash)
>>> +                       modulo slave count
>>> +
>>
>>
>> Wouldn't it be beneficial to include the ipv6 flow label in the hash
>> calculation?
>
> Hannes,
>
> In all of the traffic I inspected I don't believe I saw a single flow label
> set. Even if it were set 100% of the time by Linux, any packets routed or
> bridged from another operating system wouldn't see any benefit. The current
> algorithm distributes the traffic very well, I don't believe adding the flow
> label would be beneficial even if it were set more frequently.
>
> If you feel strongly about its inclusion, though, I am willing to
> reconsider.

It would definitely help to load balance tunnelled traffic over a
bonded interface. But as I currently don't use such a setup, I don't
have a strong opinion on that.

Greetings,

  Hannes
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