netdev - Re: [PATCH v3 02/12] netlink: spec: add shaper YAML spec

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Message-ID: <m2v80jnpkd.fsf@gmail.com>
Date: Fri, 02 Aug 2024 12:15:30 +0100
From: Donald Hunter <donald.hunter@...il.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org,  Jakub Kicinski <kuba@...nel.org>,  Jiri Pirko
 <jiri@...nulli.us>,  Madhu Chittim <madhu.chittim@...el.com>,  Sridhar
 Samudrala <sridhar.samudrala@...el.com>,  Simon Horman <horms@...nel.org>,
  John Fastabend <john.fastabend@...il.com>,  Sunil Kovvuri Goutham
 <sgoutham@...vell.com>,  Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH v3 02/12] netlink: spec: add shaper YAML spec

Paolo Abeni <pabeni@...hat.com> writes:

> On 7/31/24 23:13, Donald Hunter wrote:
>> Paolo Abeni <pabeni@...hat.com> writes:
>> 
>>> +        name: inputs
>>> +        type: nest
>>> +        multi-attr: true
>>> +        nested-attributes: ns-info
>>> +        doc: |
>>> +           Describes a set of inputs shapers for a @group operation
>> The @group renders exactly as-is in the generated htmldocs. There may be
>> a more .rst friendly markup you can use that will render better.
>
> Uhm... AFAICS the problem is the target (e.g. 'group') is outside the htmldoc section itself, I
> can't find any existing markup to serve this purpose well. What about sticking to quotes ''
> everywhere?
>
> FTR, I used @ following the kdoc style.

Yeah, I was just thinking of using .rst markup like ``code`` or
`italics`, but the meaning of @ is pretty obvious when reading the spec.
If you stick with @ then we could always teach ynl-to-rst to render it
as ``code``.

>
> [...]
>>> +    -
>>> +      name: group
>>> +      doc: |
>>> +        Group the specified input shapers under the specified
>>> +        output shaper, eventually creating the latter, if needed.
>>> +        Input shapers scope must be either @queue or @detached.
>> It says above that you cannot create a detached shaper, so how do you
>> create one to use as an input shaper here? Is this group op more like a
>> multi-create op?
>
> The group operation has the main goal of configuring a single WRR or SP scheduling group
> atomically. It can creates the needed shapers as needed, see below.
>
> The need for such operation sparks from some H/W constraints:
>
> https://lore.kernel.org/netdev/9dd818dc-1fef-4633-b388-6ce7272f9cb4@lunn.ch/
>
>>> +        Output shaper scope must be either @detached or @netdev.
>>> +        When using an output @detached scope shaper, if the
>>> +        @handle @id is not specified, a new shaper of such scope
>>> +        is created and, otherwise the specified output shaper
>>> +        must be already existing.
>>> +        The operation is atomic, on failures the extack is set
>>> +        accordingly and no change is applied to the device
>>> +        shaping configuration, otherwise the output shaper
>>> +        handle is provided as reply.
>>> +      attribute-set: net-shaper
>>> +      flags: [ admin-perm ]
>> Does there need to be a reciprocal 'ungroup' operation? Without it,
>> create / group / delete seems like they will have ambiguous semantics.
>
> I guess we need a better description. Can you please tell where/how the current one is
> ambiguous?

My expectation for 'group' would be to group existing things, with a
reciprocal 'ungroup' operation. I think you intend 'group' to both be
able to group existing shapers/groups and create a group of shapers.

Am I right in saying that delete lets you delete something from a group
(with side-effect of deleting group if it becomes empty), or delete a
whole group?

It feels a lot like each of 'set', 'group' and 'delete' are doing
multiple things and the interaction between them all becomes challenging
to describe, or to handle all the corner cases. I think part of the
problem is the mixed terminology of input, output for groups, handle,
parent for shapers and using detached to differentiate from 'implicitly
attached to a resource'.

Perhaps the API would be better if you had:

- shaper-new
- shaper-delete
- shaper-get/dump
- shaper-set
- group-new
- group-delete
- group-get/dump
- group-set

If you went with Jakub's suggestion to give every shaper n x inputs and
an output, then you could recombine groups and shapers and just have 4
ops. And you could rename 'detached' to 'shaper' so that an attachment
is one of port, netdev, queue or shaper.