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

[Jose Abreu]

From: Andre Guedes <andre.guedes@xxxxxxxxxxxxxxx>
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 ?

> 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.

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Thanks,
Jose Miguel Abreu