netdev - Re: [PATCH net-next v4 1/6] net: ethtool: allow symmetric-xor RSS hash for any flow type

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Date: Mon, 16 Oct 2023 16:30:59 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Alexander Duyck <alexander.duyck@...il.com>
Cc: Ahmed Zaki <ahmed.zaki@...el.com>, netdev@...r.kernel.org,
 intel-wired-lan@...ts.osuosl.org, corbet@....net,
 jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
 davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 vladimir.oltean@....com, andrew@...n.ch, horms@...nel.org,
 mkubecek@...e.cz, willemdebruijn.kernel@...il.com,
 linux-doc@...r.kernel.org, Wojciech Drewek <wojciech.drewek@...el.com>
Subject: Re: [PATCH net-next v4 1/6] net: ethtool: allow symmetric-xor RSS
 hash for any flow type

On Mon, 16 Oct 2023 15:55:21 -0700 Alexander Duyck wrote:
> It would make more sense to just add it as a variant hash function of
> toeplitz. If you did it right you could probably make the formatting
> pretty, something like:
> RSS hash function:
>     toeplitz: on
>         symmetric xor: on
>     xor: off
>     crc32: off
> 
> It doesn't make sense to place it in the input flags and will just
> cause quick congestion as things get added there. This is an algorithm
> change so it makes more sense to place it there.

Algo is also a bit confusing, it's more like key pre-processing?
There's nothing toeplitz about xoring input fields. Works as well
for CRC32.. or XOR.

We can use one of the reserved fields of struct ethtool_rxfh to carry
this extension. I think I asked for this at some point, but there's
only so much repeated feedback one can send in a day :(