netdev - Re: [PATCH net-next] ipv4: use l4 hash for locally generated multipath flows

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Date:	Thu, 29 Oct 2015 08:37:34 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Paolo Abeni <pabeni@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Peter Nørlund <pch@...bogen.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net-next] ipv4: use l4 hash for locally generated
 multipath flows

On Thu, Oct 29, 2015 at 8:00 AM, Paolo Abeni <pabeni@...hat.com> wrote:
> On Thu, 2015-10-29 at 07:31 -0700, Eric Dumazet wrote:
>> On Wed, 2015-10-28 at 18:39 +0100, Paolo Abeni wrote:
>> > This patch changes how the multipath hash is computed for locally
>> > generated UDP or TCP flows: now the hash comprises also l4 information
>> > (source and destination port).
>> >
>> > This allows better utilization of the available paths when the existing
>> > flows have the same source IP and the same destination IP: with l3 hash,
>> > even when multiple connections are in place simultaneously, a single path
>> > will be used, while with l4 hash we can use all the available paths.
>> >
>> > Signed-off-by: Paolo Abeni <pabeni@...hat.com>
>>
>> Please note that many skb already have a l4 hash. No need to perform yet
>> another dissection.
>
> This patch do not add dissection code: it use the information provided
> by the available flowi4 structure. Moreover the skb is not available on
> the calling site (in __ip_route_output_key_hash) and pushing it all the
> way will require a lot of intrusive changes. Do you think it's the
> better option ?
>
If there is an associated skb then skb_get_hash should be called to
get the hash. If you only have the flow structure then
get_hash_from_flowi4 (or skb_get_hash_flowi6 for IPv6 should be
called).

Tom

> Paolo
>
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