Subject: Re: [PATCH net-next v2 1/6] net: ethtool: allow symmetric RSS hash for any flow type

From: Jakub Kicinski <[email-masked]>
Date: Fri, 6 Oct 2023 17:22:48 -0700

On Fri,  6 Oct 2023 16:47:21 -0600 Ahmed Zaki wrote:
> Symmetric RSS hash functions are beneficial in applications that monitor
> both Tx and Rx packets of the same flow (IDS, software firewalls, ..etc).
> Getting all traffic of the same flow on the same RX queue results in
> higher CPU cache efficiency.
> 
> Only fields that has counterparts in the other direction can be
> accepted; IP src/dst and L4 src/dst ports.
> 
> The user may request RSS hash symmetry for a specific flow type, via:
> 
>     # ethtool -N|-U eth0 rx-flow-hash <flow_type> s|d|f|n symmetric
> 
> or turn symmetry off (asymmetric) by:
> 
>     # ethtool -N|-U eth0 rx-flow-hash <flow_type> s|d|f|n

Thanks for the changes, code looks good!

The question left unanswered is whether we should care about the exact
implementation of the symmetry (xor, xor duplicate, sort fields).
Toeplitz-based RSS is very precisely specified, so we may want to carry
that precision into the symmetric behavior. I have a weak preference 
to do so... but no willingness to argue with you, so let me put Willem
on the spot and have him make a decision :)

Please make sure to CC Willem and anyone else who commented on previous
revisions on future versions!