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

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Date:   Thu, 29 Sep 2022 09:12:59 +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

Wed, Sep 28, 2022 at 01:47:03PM CEST, michal.wilczynski@...el.com wrote:
>
>
>On 9/26/2022 1:51 PM, Jiri Pirko wrote:
>> 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?
>
>Yes.

Why do you have this mismatch? If forces the hypervisor and VM admin to
somehow sync upon the configuration. That does not sound correct to me.


>
>> 
>> 
>> > 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?
>
> Correct ;)

Okay. So you don't really need any kind of sharing devlink might be able
to provide.

>From what you say and how I see this, it's clear. You should handle the
per-queue shaping on the VM, on netdevice level, most probably by
offloading some of the TC qdisc.


>
>> 
>> 
>> > 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
>> > 
>> > 
>