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: <70132b6f-542f-4fe6-971f-ab9ea80acbe4@nvidia.com>
Date: Tue, 31 Oct 2023 16:45:31 +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 31/10/2023 16:40, Ahmed Zaki wrote:
> 
> 
> On 2023-10-31 06:00, Gal Pressman wrote:
>> 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.
> 
> Sure. I will add more ice-specific doc in:
> Documentation/networking/device_drivers/ethernet/intel/ice.rst

I was thinking of somewhere more generic, where ethtool users (not
necessarily ice users) can refer to.

Perhaps Documentation/networking/ethtool-netlink.rst? Or ethtool man page?