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

From: Jakub Kicinski <[email-masked]>
Date: Wed, 24 May 2023 08:38:13 -0700

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).