netdev - Re: [RFC net-next v2 1/2] devlink: add whole device devlink instance

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Message-ID: <20250220174512.578eebe8@kernel.org>
Date: Thu, 20 Feb 2025 17:45:12 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Przemek Kitszel <przemyslaw.kitszel@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, Tony Nguyen
 <anthony.l.nguyen@...el.com>, Jiri Pirko <jiri@...nulli.us>, Cosmin Ratiu
 <cratiu@...dia.com>, Tariq Toukan <tariqt@...dia.com>,
 netdev@...r.kernel.org, Konrad Knitter <konrad.knitter@...el.com>, Jacob
 Keller <jacob.e.keller@...el.com>, davem@...emloft.net, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Andrew Lunn
 <andrew@...n.ch>, linux-kernel@...r.kernel.org, ITP Upstream
 <nxne.cnse.osdt.itp.upstreaming@...el.com>, Carolina Jubran
 <cjubran@...dia.com>
Subject: Re: [RFC net-next v2 1/2] devlink: add whole device devlink
 instance

On Wed, 19 Feb 2025 17:32:54 +0100 Przemek Kitszel wrote:
> Add a support for whole device devlink instance. Intented as a entity
> over all PF devices on given physical device.
> 
> In case of ice driver we have multiple PF devices (with their devlink
> dev representation), that have separate drivers loaded. However those
> still do share lots of resources due to being the on same HW. Examples
> include PTP clock and RSS LUT. Historically such stuff was assigned to
> PF0, but that was both not clear and not working well. Now such stuff
> is moved to be covered into struct ice_adapter, there is just one instance
> of such per HW.
> 
> This patch adds a devlink instance that corresponds to that ice_adapter,
> to allow arbitrage over resources (as RSS LUT) via it (further in the
> series (RFC NOTE: stripped out so far)).
> 
> Thanks to Wojciech Drewek for very nice naming of the devlink instance:
> PF0:		pci/0000:00:18.0
> whole-dev:	pci/0000:00:18
> But I made this a param for now (driver is free to pass just "whole-dev").

Which only works nicely if you're talking about functions not full
separate links :) When I was thinking about it a while back my
intuition was that we should have a single instance, just accessible
under multiple names. But I'm not married to that direction if there
are problems with it.

> $ devlink dev # (Interesting part of output only)
> pci/0000:af:00:
>   nested_devlink:
>     pci/0000:af:00.0
>     pci/0000:af:00.1
>     pci/0000:af:00.2
>     pci/0000:af:00.3
>     pci/0000:af:00.4
>     pci/0000:af:00.5
>     pci/0000:af:00.6
>     pci/0000:af:00.7

Could you go into more details on what stays on the "nested" instances
and what moves to the "whole-dev"? Jiri recently pointed out to y'all
cases where stuff that should be a port attribute was an instance
attribute.