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

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Date:   Fri, 10 Jan 2020 14:35:41 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     Andre Guedes <andre.guedes@...ux.intel.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Murali Karicheri <m-karicheri2@...com>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>
CC:     Po Liu <po.liu@....com>,
        "alexandru.ardelean@...log.com" <alexandru.ardelean@...log.com>,
        "allison@...utok.net" <allison@...utok.net>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "ayal@...lanox.com" <ayal@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "hauke.mehrtens@...el.com" <hauke.mehrtens@...el.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "jiri@...lanox.com" <jiri@...lanox.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "pablo@...filter.org" <pablo@...filter.org>,
        "saeedm@...lanox.com" <saeedm@...lanox.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        Vladimir Oltean <vladimir.oltean@....com>,
        "simon.horman@...ronome.com" <simon.horman@...ronome.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandru Marginean <alexandru.marginean@....com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Roy Zang <roy.zang@....com>, Mingkai Hu <mingkai.hu@....com>,
        Jerry Huang <jerry.huang@....com>, Leo Li <leoyang.li@....com>,
        Joao Pinto <Joao.Pinto@...opsys.com>
Subject: RE: [EXT] Re: [v1,net-next, 1/2] ethtool: add setting frame
 preemption of traffic classes

From: Andre Guedes <andre.guedes@...ux.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@...ux.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