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SubjectRE: [EXT] Re: [v1,net-next, 1/2] ethtool: add setting frame preemption of traffic classes
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From: Andre Guedes <andre.guedes@linux.intel.com>
Date: Jan/09/2020, 18:04:55 (UTC+00:00)

> 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.

OK. Should we ask to merge it as-is then ?

> > > 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.

I'm afraid its not available unless you are a Synopsys customer. You
should however be able to figure out the behavior by reading my patch
that adds support for FPE in XGMAC and QoS cores. I can clarify any
doubts.

---
Thanks,
Jose Miguel Abreu
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