netdev - Re: [RFC PATCH net-next v4 2/6] devlink: Extend devlink-rate api with queues and new parameters

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Date:   Mon, 26 Sep 2022 13:51:24 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     "Wilczynski, Michal" <michal.wilczynski@...el.com>
Cc:     Edward Cree <ecree.xilinx@...il.com>, netdev@...r.kernel.org,
        alexandr.lobakin@...el.com, dchumak@...dia.com, maximmi@...dia.com,
        simon.horman@...igine.com, jacob.e.keller@...el.com,
        jesse.brandeburg@...el.com, przemyslaw.kitszel@...el.com
Subject: Re: [RFC PATCH net-next v4 2/6] devlink: Extend devlink-rate api
 with queues and new parameters

Thu, Sep 15, 2022 at 08:41:52PM CEST, michal.wilczynski@...el.com wrote:
>
>
>On 9/15/2022 5:31 PM, Edward Cree wrote:
>> On 15/09/2022 14:42, Michal Wilczynski wrote:
>> > Currently devlink-rate only have two types of objects: nodes and leafs.
>> > There is a need to extend this interface to account for a third type of
>> > scheduling elements - queues. In our use case customer is sending
>> > different types of traffic on each queue, which requires an ability to
>> > assign rate parameters to individual queues.
>> Is there a use-case for this queue scheduling in the absence of a netdevice?
>> If not, then I don't see how this belongs in devlink; the configuration
>>   should instead be done in two parts: devlink-rate to schedule between
>>   different netdevices (e.g. VFs) and tc qdiscs (or some other netdev-level
>>   API) to schedule different queues within each single netdevice.
>> Please explain why this existing separation does not support your use-case.
>> 
>> Also I would like to see some documentation as part of this patch.  It looks
>>   like there's no kernel document for devlink-rate unlike most other devlink
>>   objects; perhaps you could add one?
>> 
>> -ed
>
>Hi,
>Previously we discussed adding queues to devlink-rate in this thread:
>https://lore.kernel.org/netdev/20220704114513.2958937-1-michal.wilczynski@intel.com/T/#u
>In our use case we are trying to find a way to expose hardware Tx scheduler
>tree that is defined
>per port to user. Obviously if the tree is defined per physical port, all the
>scheduling nodes will reside
>on the same tree.
>
>Our customer is trying to send different types of traffic that require
>different QoS levels on the same

Do I understand that correctly, that you are assigning traffic to queues
in VM, and you rate the queues on hypervisor? Is that the goal?


>VM, but on a different queues. This requires completely different rate setups
>for that queue - in the
>implementation that you're mentioning we wouldn't be able to arbitrarily
>reassign the queue to any node.
>Those queues would still need to share a single parent - their netdev. This

So that replies to Edward's note about having the queues maintained
within the single netdev/vport, correct?


>wouldn't allow us to fully take
>advantage of the HQoS and would introduce arbitrary limitations.
>
>Also I would think that since there is only one vendor implementing this
>particular devlink-rate API, there is
>some room for flexibility.
>
>Regarding the documentation,  sure. I just wanted to get all the feedback
>from the mailing list and arrive at the final
>solution before writing the docs.
>
>BTW, I'm going to be out of office tomorrow, so will respond in this thread
>on Monday.
>BR,
>Michał
>
>