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

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Date:   Tue, 11 Oct 2022 16:17:55 +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,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [RFC PATCH net-next v4 2/6] devlink: Extend devlink-rate api
 with queues and new parameters

Tue, Oct 11, 2022 at 03:28:38PM CEST, michal.wilczynski@...el.com wrote:
>
>
>On 9/29/2022 9:12 AM, Jiri Pirko wrote:
>> 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.
>
>Thanks for a feedback, this is going to be changed
>
>> 
>> 
>> > > 
>> > > > 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.
>
>I talked with architect, and this is how the solution will end up looking
>like,
>I'm not sure however whether creating a hardware-only qdisc is allowed ?

Nope.


>
>
>
>Btw, thanks everyone for valuable feedback, I've resend the patch
>without the queue support,
>https://lore.kernel.org/netdev/20221011090113.445485-1-michal.wilczynski@intel.com/
>
>
>BR,
>Michał
>> 
>> > > 
>> > > > 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
>> > > > 
>> > > > 
>