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 18:08:32 -0600
From: Ahmed Zaki <ahmed.zaki@...el.com>
To: Jakub Kicinski <kuba@...nel.org>, Alexander Duyck
	<alexander.duyck@...il.com>
CC: <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 2023-10-16 17:30, Jakub Kicinski wrote:
> 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 :(

Sorry you felt that. I took you comment [1]:

"Using hashing algo for configuring fields feels like a dirty hack".

To mean that the we should not use the hfunc API ("ethtool_rxfh"). This 
is why in the new series I chose to configure the RSS fields. This also 
provides the user with more control and better granularity on which 
flow-types to be symmetric, and which protocols (L3 and/or L4) to use. I 
have no idea how to do any of these via hfunc/ethtool_rxfh API so it 
seemed a better approach.

I see you marked the series as "Changes Requested". I will send a new 
version tomorrow and move the sanity checks inside ice_ethtool.


[1]: https://lore.kernel.org/netdev/20230824174336.6fb801d5@kernel.org/