netdev - Re: [PATCH net] net: sched: fix warn on htb offloaded class creation

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Date: Mon, 13 Nov 2023 16:21:20 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Maxim Mikityanskiy <maxtram95@...il.com>, Jiri Pirko <jiri@...nulli.us>
Cc: "Chittim, Madhu" <madhu.chittim@...el.com>, netdev@...r.kernel.org, 
 Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Tariq Toukan
 <tariqt@...dia.com>, Gal Pressman <gal@...dia.com>,  Saeed Mahameed
 <saeedm@...dia.com>, xuejun.zhang@...el.com, sridhar.samudrala@...el.com
Subject: Re: [PATCH net] net: sched: fix warn on htb offloaded class creation

On Mon, 2023-11-13 at 16:51 +0200, Maxim Mikityanskiy wrote:
> On Sun, 12 Nov 2023 at 09:48:19 +0100, Paolo Abeni wrote:
> > On Fri, 2023-11-10 at 13:07 +0200, Maxim Mikityanskiy wrote:
> > > On Thu, 09 Nov 2023 at 13:54:17 -0800, Chittim, Madhu wrote:
> > > > We would like to enable Tx rate limiting using htb offload on all the
> > > > existing queues.
> > > 
> > > I don't seem to understand how you see it possible with HTB.
> > 
> > I must admit I feel sorry for not being able to join any of the
> > upcoming conferences, but to me it looks like there is some
> > communication gap that could be filled by in-person discussion.
> > 
> > Specifically the above to me sounds contradictory to what you stated
> > here:
> > 
> > https://lore.kernel.org/netdev/ZUEQzsKiIlgtbN-S@mail.gmail.com/
> > 
> > """
> > > Can HTB actually configure H/W shaping on
> > > real_num_tx_queues?
> > 
> > It will be on real_num_tx_queues, but after it's increased to add new
> > HTB queues. The original queues [0, N) are used for direct traffic,
> > same as the non-offloaded HTB's direct_queue (it's not shaped).
> > """
> 
> Sorry if that was confusing, there is actually no contradition, let me
> rephrase. Queues number [0, orig_real_num_tx_queues) are direct, they
> are not shaped, they correspond to HTB's unclassified traffic. Queues
> number [orig_real_num_tx_queues, real_num_tx_queues) correspond to HTB
> classes and are shaped. Here orig_real_num_tx_queues is how many queues
> the netdev had before HTB offload was attached. It's basically the
> standard set of queues, and HTB creates a new queue per class. Let me
> know if that helps.
> 
> > > What is your goal? 
> > 
> > We are looking for clean interface to configure individually min/max
> > shaping on each TX queue for a given netdev (actually virtual
> > function).
> 
> Have you tried tc mqprio? If you set `mode channel` and create queue
> groups with only one queue each, you can set min_rate and max_rate for
> each group (==queue), and it works with the existing set of queues.

mqprio does not fit well here as:

* enforce an hard limit of 16 queues imposed by uAPI
* traffic class/queue selection depends on skb priority. That does not
fit well if e.g. the user would rely on a 1to1 CPU to queue mapping.

It looks like any existing scheduler would need some extension to fit
this use case.

@Jiri: when you suggested TC do you have anything specific in your
mind?

Otherwise it looks like extending /sys/class/net/eth0/queues/tx-
*/tx_maxrate would be more straight-forward to me.

Thanks!

Paolo