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

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Message-ID: <d097e7d3-5e16-44ba-aa92-dfb7fbedc600@nvidia.com>
Date: Tue, 31 Oct 2023 14:00:45 +0200
From: Gal Pressman <gal@...dia.com>
To: Ahmed Zaki <ahmed.zaki@...el.com>, Jakub Kicinski <kuba@...nel.org>,
 Alexander H Duyck <alexander.duyck@...il.com>
Cc: mkubecek@...e.cz, andrew@...n.ch, willemdebruijn.kernel@...il.com,
 Wojciech Drewek <wojciech.drewek@...el.com>, corbet@....net,
 netdev@...r.kernel.org, linux-doc@...r.kernel.org,
 jesse.brandeburg@...el.com, edumazet@...gle.com, anthony.l.nguyen@...el.com,
 horms@...nel.org, vladimir.oltean@....com,
 Jacob Keller <jacob.e.keller@...el.com>, intel-wired-lan@...ts.osuosl.org,
 pabeni@...hat.com, davem@...emloft.net
Subject: Re: [Intel-wired-lan] [PATCH net-next v4 1/6] net: ethtool: allow
 symmetric-xor RSS hash for any flow type

On 29/10/2023 18:59, Ahmed Zaki wrote:
> 
> 
> On 2023-10-29 06:48, Gal Pressman wrote:
>> On 29/10/2023 14:42, Ahmed Zaki wrote:
>>>
>>>
>>> On 2023-10-29 06:25, Gal Pressman wrote:
>>>> On 21/10/2023 3:00, Ahmed Zaki wrote:
>>>>>
>>>>>
>>>>> On 2023-10-20 17:49, Jakub Kicinski wrote:
>>>>>> On Fri, 20 Oct 2023 17:14:11 -0600 Ahmed Zaki wrote:
>>>>>>> I replied to that here:
>>>>>>>
>>>>>>> https://lore.kernel.org/all/afb4a06f-cfba-47ba-adb3-09bea7cb5f00@intel.com/
>>>>>>>
>>>>>>> I am kind of confused now so please bear with me. ethtool either
>>>>>>> sends
>>>>>>> "ethtool_rxfh" or "ethtool_rxnfc". AFAIK "ethtool_rxfh" is the
>>>>>>> interface
>>>>>>> for "ethtool -X" which is used to set the RSS algorithm. But we
>>>>>>> kind of
>>>>>>> agreed to go with "ethtool -U|-N" for symmetric-xor, and that uses
>>>>>>> "ethtool_rxnfc" (as implemented in this series).
>>>>>>
>>>>>> I have no strong preference. Sounds like Alex prefers to keep it
>>>>>> closer
>>>>>> to algo, which is "ethtool_rxfh".
>>>>>>
>>>>>>> Do you mean use "ethtool_rxfh" instead of "ethtool_rxnfc"? how would
>>>>>>> that work on the ethtool user interface?
>>>>>>
>>>>>> I don't know what you're asking of us. If you find the code to
>>>>>> confusing
>>>>>> maybe someone at Intel can help you :|
>>>>>
>>>>> The code is straightforward. I am confused by the requirements: don't
>>>>> add a new algorithm but use "ethtool_rxfh".
>>>>>
>>>>> I'll see if I can get more help, may be I am missing something.
>>>>>
>>>>
>>>> What was the decision here?
>>>> Is this going to be exposed through ethtool -N or -X?
>>>
>>> I am working on a new version that uses "ethtool_rxfh" to set the
>>> symmetric-xor. The user will set per-device via:
>>>
>>> ethtool -X eth0 hfunc toeplitz symmetric-xor
>>>
>>> then specify the per-flow type RSS fields as usual:
>>>
>>> ethtool -N|-U eth0 rx-flow-hash <flow_type> s|d|f|n
>>>
>>> The downside is that all flow-types will have to be either symmetric or
>>> asymmetric.
>>
>> Why are we making the interface less flexible than it can be with -N?
> 
> Alexander Duyck prefers to implement the "symmetric-xor" interface as an
> algorithm or extension (please refer to previous messages), but ethtool
> does not provide flowtype/RSS fields setting via "-X". The above was the
> best solution that we (at Intel) could think of.

OK, it's a weird we're deliberately limiting our interface, given
there's already hardware that supports controlling symmetric hashing per
flow type.

I saw you mentioned the way ice hardware implements symmetric-xor
somewhere, it definitely needs to be added somewhere in our
documentation to prevent confusion.
mlx5 hardware also does symmetric hashing with xor, but not exactly as
you described, we need the algorithm to be clear.