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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Date: Tue, 31 Oct 2023 08:40:06 -0600
From: Ahmed Zaki <ahmed.zaki@...el.com>
To: Gal Pressman <gal@...dia.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 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