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: <a2a1164f-1492-43d1-9667-5917d0ececcb@intel.com>
Date: Sun, 29 Oct 2023 10:59:42 -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 2023-10-29 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.


Another solution would be to add a similar flowtype interface to "-X":

ethtool -X eth0 hfunc toeplitz [symmetric-xor rx-flow-hash <flow_type>]

which will allow the user to set "symmetric-xor" per flow-type. IMHO 
such approach is confusing; consider if the user sets:

ethtool -X eth0 ALG-1 symmetric-xor rx-flow-hash tcp4

and then:

ethtool -X eth0 ALG-2

should we switch tcp4 to ALG-2? Also, just the idea of replicating 
"rx-flow-hash" did not sound good overall to me.


Anyway, we thought that, if we are using "-X", then limiting all 
flow-types to whatever is set with "-X" is cleaner and works best with 
the current ethtool design. Any other suggestions are welcome of course.