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 09:14:58 -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 08:45, Gal Pressman wrote:
> 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?

Do you mean add vendor-specific implementation details to common docs? 
Not sure if I have seen this before. Any examples?

Or, we can add a note in ethtool doc that each vendor's implementation 
is different and "Refer to your vendor's specifications for more info".