linux-kernel - Re: [PATCH net-next 03/10] devlink: Serialize access to rate domains

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Message-ID: <20250304160412.50e5b6b8@kernel.org>
Date: Tue, 4 Mar 2025 16:04:12 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Tariq Toukan <tariqt@...dia.com>, "David S. Miller"
 <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, Eric Dumazet
 <edumazet@...gle.com>, Andrew Lunn <andrew+netdev@...n.ch>, Jiri Pirko
 <jiri@...dia.com>, Cosmin Ratiu <cratiu@...dia.com>, Carolina Jubran
 <cjubran@...dia.com>, Gal Pressman <gal@...dia.com>, Mark Bloch
 <mbloch@...dia.com>, Donald Hunter <donald.hunter@...il.com>, Jonathan
 Corbet <corbet@....net>, Saeed Mahameed <saeedm@...dia.com>, Leon
 Romanovsky <leon@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next 03/10] devlink: Serialize access to rate
 domains

On Tue, 4 Mar 2025 14:11:40 +0100 Jiri Pirko wrote:
> Mon, Mar 03, 2025 at 11:06:23PM +0100, kuba@...nel.org wrote:
> >On Thu, 27 Feb 2025 13:22:25 +0100 Jiri Pirko wrote:  
> >> Depends. On normal host sr-iov, no. On smartnic where you have PF in
> >> host, yes.  
> >
> >Yet another "great choice" in mlx5 other drivers have foreseen
> >problems with and avoided.  
> 
> What do you mean? How else to model it? Do you suggest having PF devlink
> port for the PF that instantiates? That would sound like Uroboros to me.

I reckon it was always more obvious to those of us working on
NPU-derived devices, to which a PCIe port is just a PCIe port,
with no PCIe<>MAC "pipeline" to speak of.

The reason why having the "PF port" is a good idea is exactly
why we're having this conversation. If you don't you'll assign
to the global scope attributes which are really just port attributes.

> >> Looks like pretty much all current NICs are multi-PFs, aren't they?  
> >
> >Not in a way which requires cross-port state sharing, no.
> >You should know this.  
> 
> This is not about cross-port state sharing. This is about per-PF
> configuration. What am I missing?

Maybe we lost the thread of the conversation.. :)
I'm looking at the next patch in this series and it says:

  devlink: Introduce shared rate domains

  The underlying idea is modeling a piece of hardware which:
  1. Exposes multiple functions as separate devlink objects.
  2. Is capable of instantiating a transmit scheduling tree spanning
     multiple functions.

  Modeling this requires devlink rate nodes with parents across other
  devlink objects.

Are these domains are not cross port?