netdev - Re: [RFC PATCH v3 net-next] Documentation: devlink: Add devlink-sd

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Message-ID: <Zc8Zo0rCBzmGqTLf@nanopsycho>
Date: Fri, 16 Feb 2024 09:15:31 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Jacob Keller <jacob.e.keller@...el.com>, William Tu <witu@...dia.com>,
	bodong@...dia.com, jiri@...dia.com, netdev@...r.kernel.org,
	saeedm@...dia.com,
	"aleksander.lobakin@...el.com" <aleksander.lobakin@...el.com>
Subject: Re: [RFC PATCH v3 net-next] Documentation: devlink: Add devlink-sd

Fri, Feb 16, 2024 at 03:07:29AM CET, kuba@...nel.org wrote:
>On Thu, 15 Feb 2024 09:41:31 -0800 Jacob Keller wrote:
>> I don't know offhand if we have a device which can share pools
>> specifically, but we do have multi-PF devices which have a lot of shared
>> resources. However, due to the multi-PF PCIe design. I looked into ways
>> to get a single devlink across the devices.. but ultimately got stymied
>> and gave up.
>> 
>> This left us with accepting the limitation that each PF gets its own
>> devlink and can't really communicate with other PFs.
>> 
>> The existing solution has just been to partition the shared resources
>> evenly across PFs, typically via firmware. No flexibility.
>> 
>> I do think the best solution here would be to figure out a generic way
>> to tie multiple functions into a single devlink representing the device.
>> Then each function gets the set of devlink_port objects associated to
>> it. I'm not entirely sure how that would work. We could hack something
>> together with auxbus.. but thats pretty ugly. Some sort of orchestration
>> in the PCI layer that could identify when a device wants to have some
>> sort of "parent" driver which loads once and has ties to each of the
>> function drivers would be ideal.
>> 
>> Then this parent driver could register devlink, and each function driver
>> could connect to it and allocate ports and function-specific resources.
>> 
>> Alternatively a design which loads a single driver that maintains
>> references to each function could work but that requires a significant
>> change to the entire driver design and is unlikely to be done for
>> existing drivers...
>
>I think the complexity mostly stems from having to answer what the
>"right behavior" is. At least that's what I concluded when thinking
>about it back at Netronome :)  If you do a strict hierarchy where
>one PF is preassigned the role of the leader, and just fail if anything
>unexpected happens - it should be doable. We already kinda have the
>model where devlink is the "first layer of probing" and "reload_up()"
>is the second.
>
>Have you had a chance to take a closer look at mlx5 "socket direct"
>(rename pending) implementation?
>
>BTW Jiri, weren't you expecting that to use component drivers or some
>such?

IIRC, turned out that was not suitable for this case by my colleagues.
You have to ask them why, I don't recall.

But socket direct is a different kind of story. There 2/n PFs are just
separate NUMA PCI channels to a single FW entity.