netdev - Re: [PATCH net-next 2/2] bonding: use l4 hash if available

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Message-ID: <CALx6S37WgoNp-mgSHFmDc0dW1ozKt-5kNV4+j4oPekebVz8JVQ@mail.gmail.com>
Date:	Tue, 15 Sep 2015 17:15:34 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Mahesh Bandewar <maheshb@...gle.com>
Subject: Re: [PATCH net-next 2/2] bonding: use l4 hash if available

On Tue, Sep 15, 2015 at 5:03 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2015-09-15 at 16:45 -0700, Tom Herbert wrote:
>> > +       if (bond->params.xmit_policy == BOND_XMIT_POLICY_ENCAP34 &&
>> > +           skb->l4_hash)
>> > +                       return skb->hash;
>> > +
>> >         if (bond->params.xmit_policy == BOND_XMIT_POLICY_LAYER2 ||
>> >             !bond_flow_dissect(bond, skb, &flow))
>> >                 return bond_eth_hash(skb);
>> >
>> >
>> Ugh, bond_flow_dissect is yet another instance of customized flow
>> dissection! We should really clean this up. I suggest that in cases
>> were we want L4 hash a call to skb_get_hash should suffice. We can
>> create skb_get_l3hash when caller explicitly wants an L3 hash-- this
>> would return skb->hash if it's valid and skb->l4_hash is not set, else
>> call flow dissector with FLOW_DISSECTOR_F_STOP_AT_L3 and then do the
>> normal hash over flow keys (don't save result in skb->hash in this
>> case).
>
> This code predates all the change you did recently ;)
>
A more fundamental question is whether we can eliminate some of these
hashing types (I see five of them in if_bonding.h). Is there any
substantial difference between this and IPv4/v6 ECMP routing such that
they shouldn't all have the same path selection modes?

Tom

> BTW, the simple xor weakness is showing up after
> our change favoring even ports at connect() time, for a bonding device
> with 2 or 4 slaves.
>
> (commit 07f4c90062f8fc7c8c26f8f95324cbe8fa3145a5
> "tcp/dccp: try to not exhaust ip_local_port_range in connect()")
>
>
>
>
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