RE: [EXT] Re: [v1,net-next, 1/2] ethtool: add setting frame preemption of traffic classes

Andre Guedes
2020-01-09T18:05:00Z

Hi Jose,

Quoting Jose Abreu (2020-01-09 00:59:24)
> From: Andre Guedes <andre.guedes@linux.intel.com>
> Date: Jan/09/2020, 01:07:37 (UTC+00:00)
>
> > After reading all this great discussion and revisiting the 802.1Q and 802.3br
> > specs, I'm now leaning towards to not coupling Frame Preemption support under
> > taprio qdisc. Besides what have been discussed, Annex S.2 from 802.1Q-2018
> > foresees FP without EST so it makes me feel like we should keep them separate.
>
> I agree that EST and FP can be used individually. But how can you
> specify the hold and release commands for gates without changing taprio qdisc user space API ?

The 'hold' and 'release' are operations from the GCL, which is part of EST. So
they should still be specified via taprio. No changing in the user space API is
required since these operations are already supported in taprio API. What is
missing today is just the 'tc' side of it, which you already have a patch for
it.

> > Regarding the FP configuration knobs, the following seems reasonable to me:
> > * Enable/disable FP feature
> > * Preemptable queue mapping
> > * Fragment size multiplier
> >
> > I'm not sure about the knob 'timers (hold/release)' described in the quotes
> > above. I couldn't find a match in the specs. If it refers to 'holdAdvance' and
> > 'releaseAdvance' parameters described in 802.1Q-2018, I believe they are not
> > configurable. Do we know any hardware where they are configurable?
>
> Synopsys' HW supports reconfiguring these parameters. They are, however,
> fixed independently of Queues. i.e. all queues will have same holdAdvance / releaseAdvance.

Good to know. Is the datasheet publicly available? If so, could you please
point me to it? I'd like to learn more about the FP knobs provided by
different HW.

Regards,

Andre