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, 22 Sep 2022 13:29:45 -0700
From:   Jakub Kicinski <kuba@...nel.org>
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>, <jiri@...nulli.us>,
        <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

On Thu, 22 Sep 2022 15:45:55 +0200 Wilczynski, Michal wrote:
> On 9/22/2022 2:50 PM, Jakub Kicinski wrote:
> > Anyway. My gut feeling is that this is cutting a corner. Seems
> > most natural for the VF/PF level to be controlled by the admin
> > and the queue level by whoever owns the queue. The hypervisor
> > driver/FW should reconcile the two and compile the full hierarchy.  
> 
> We tried already tc-htb, and it doesn't work for a couple of reasons, 
> even in this potential hybrid with devlink-rate. One of the problems
> with tc-htb offload is that it forces you to allocate a new
> queue, it doesn't allow for reassigning an existing queue to another 
> scheduling node. This is our main use case.
> 
> Here's a discussion about tc-htb: 
> https://lore.kernel.org/netdev/20220704114513.2958937-1-michal.wilczynski@intel.com/

This is a problem only for "SR-IOV case" or also for just the PF?

> So either I would have to invent a new offload type (?) for tc, or 
> completely rewrite and
> probably break tc-htb that mellanox implemented.
> Also in our use case it's possible to create completely new branches 
> from the root and
> reassigning queues there. This wouldn't be possible with the method 
> you're proposing.
> 
> So existing interface doesn't allow us to do what is required.

For some definition of "what is required" which was not really
disclosed clearly. Or I'm to slow to grasp.