netdev - Re: [Intel-wired-lan] [PATCH iwl-next v4 0/5] iavf: Add devlink and devlink rate support'

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Date: Thu, 14 Dec 2023 21:29:51 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>, Jiri Pirko <jiri@...nulli.us>
Cc: netdev@...r.kernel.org, anthony.l.nguyen@...el.com, 
 intel-wired-lan@...ts.osuosl.org, qi.z.zhang@...el.com, Wenjun Wu
 <wenjun1.wu@...el.com>, maxtram95@...il.com, "Chittim, Madhu"
 <madhu.chittim@...el.com>, "Samudrala, Sridhar"
 <sridhar.samudrala@...el.com>,  Simon Horman <simon.horman@...hat.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v4 0/5] iavf: Add devlink and
 devlink rate support'

On Mon, 2023-11-27 at 17:43 -0800, Jakub Kicinski wrote:
> On Mon, 27 Nov 2023 16:15:47 -0800 Zhang, Xuejun wrote:
> > This is extension of ndo_set_tx_maxrate to include per queue parameters 
> > of tx_minrate and burst.
> > 
> > devlink rate api includes tx_maxrate and tx_minrate, it is intended for 
> > port rate configurations.
> > 
> > With regarding to tc mqprio, it is being used to configure queue group 
> > per tc.
> > 
> > For sriov ndo ndo_set_vf_rate, that has been used for overall VF rate 
> > configuration, not for queue based rate configuration.
> > 
> > It seems there are differences on intent of the aforementioned APIs.
> > 
> > Our use case here is to allow user (i.e @ uAPI) to configure tx rates of 
> > max rate & min rate per VF queue.Hence we are inclined to 
> > ndo_set_tx_maxrate extension.
> 
> I said:
> 
>   So since you asked for my opinion - my opinion is that step 1 is to
>   create a common representation of what we already have and feed it
>   to the drivers via a single interface. I could just be taking sysfs
>   maxrate and feeding it to the driver via the devlink rate interface.
>   If we have the right internals I give 0 cares about what uAPI you pick.
> 
> https://lore.kernel.org/all/20231118084843.70c344d9@kernel.org/
> 
> Again, the first step is creating a common kernel <> driver interface
> which can be used to send to the driver the configuration from the
> existing 4 interfaces.

Together with Simon, I spent some time on the above. We think the
ndo_setup_tc(TC_SETUP_QDISC_TBF) hook could be used as common basis for
this offloads, with some small extensions (adding a 'max_rate' param,
too).

The idea would be:
- 'fixing' sch_btf so that the s/w path became a no-op when h/w offload
is enabled
- extend sch_btf to support max rate
- do the relevant ice implementation
- ndo_set_tx_maxrate could be replaced with the mentioned ndo call (the
latter interface is a strict super-set of former)
- ndo_set_vf_rate could also be replaced with the mentioned ndo call
(with another small extension to the offload data)

I think mqprio deserves it's own separate offload interface, as it
covers multiple tasks other than shaping (grouping queues and mapping
priority to classes)

In the long run we could have a generic implementation of the
ndo_setup_tc(TC_SETUP_QDISC_TBF) in term of devlink rate adding a
generic way to fetch the devlink_port instance corresponding to the
given netdev and mapping the TBF features to the devlink_rate API.

Not starting this due to what Jiri mentioned [1].

WDYT?

Thanks,

Paolo and Simon

[1] https://lore.kernel.org/netdev/ZORRzEBcUDEjMniz@nanopsycho/