netdev - Re: [PATCH net-next] nfp: add L4 RSS hashing on UDP traffic

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Message-ID: <20230524083813.65cdee0d@kernel.org>
Date: Wed, 24 May 2023 08:38:13 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Simon Horman <simon.horman@...igine.com>, Paolo Abeni
 <pabeni@...hat.com>, Louis Peens <louis.peens@...igine.com>, David Miller
 <davem@...emloft.net>, netdev@...r.kernel.org, oss-drivers@...igine.com,
 Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] nfp: add L4 RSS hashing on UDP traffic

On Wed, 24 May 2023 11:33:15 -0400 Willem de Bruijn wrote:
> The OCP draft spec already has this wording, which covers UDP:
> 
> "RSS defines two rules to derive queue selection input in a
> flow-affine manner from packet headers. Selected fields of the headers
> are extracted and concatenated into a byte array. If the packet is
> IPv4 or IPv6, not fragmented, and followed by a transport layer
> protocol with ports, such as TCP and UDP, then extract the
> concatenated 4-field byte array { source address, destination address,
> source port, destination port }. Else, if the packet is IPv4 or IPv6,
> extract 2-field byte array { source address, destination address }.
> IPv4 packets are considered fragmented if the more fragments bit is
> set or the fragment offset field is non-zero."

Ugh, that's what I thought. I swear I searched it for "fragment"
yesterday and the search came up empty. I blame google docs :|

We should probably still document the recommendation that if the NIC
does not comply and hashes on ports with MF set - it should disable 
UDP hashing by default (in kernel docs).