linux-kernel - Re: [EXT] Re: [net-next] net: dsa: felix: disable always guard band bit for TAS config

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Date:   Tue, 20 Apr 2021 13:30:51 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Xiaoliang Yang <xiaoliang.yang_1@....com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Arvid.Brodin@...n.com" <Arvid.Brodin@...n.com>,
        "m-karicheri2@...com" <m-karicheri2@...com>,
        "vinicius.gomes@...el.com" <vinicius.gomes@...el.com>,
        "michael.chan@...adcom.com" <michael.chan@...adcom.com>,
        "vishal@...lsio.com" <vishal@...lsio.com>,
        "saeedm@...lanox.com" <saeedm@...lanox.com>,
        "jiri@...lanox.com" <jiri@...lanox.com>,
        "idosch@...lanox.com" <idosch@...lanox.com>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        "ivan.khoronzhuk@...aro.org" <ivan.khoronzhuk@...aro.org>,
        "andre.guedes@...ux.intel.com" <andre.guedes@...ux.intel.com>,
        "yuehaibing@...wei.com" <yuehaibing@...wei.com>,
        "allan.nielsen@...rochip.com" <allan.nielsen@...rochip.com>,
        "joergen.andreasen@...rochip.com" <joergen.andreasen@...rochip.com>,
        "colin.king@...onical.com" <colin.king@...onical.com>,
        Po Liu <po.liu@....com>, Mingkai Hu <mingkai.hu@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Leo Li <leoyang.li@....com>
Subject: Re: [EXT] Re: [net-next] net: dsa: felix: disable always guard band
 bit for TAS config

On Tue, Apr 20, 2021 at 10:28:45AM +0000, Xiaoliang Yang wrote:
> Hi Vladimir,
> 
> On Tue, Apr 20, 2021 at 16:27:10AM +0800, Vladimir Oltean wrote:
> >
> > On Tue, Apr 20, 2021 at 03:06:40AM +0000, Xiaoliang Yang wrote:
> >> Hi Vladimir.
> >>
> >> On Mon, Apr 19, 2021 at 20:38PM +0800, Vladimir Oltean wrote:
> >> >
> >> >What is a scheduled queue? When time-aware scheduling is enabled on 
> >> >the port, why are some queues scheduled and some not?
> >>
> >> The felix vsc9959 device can set SCH_TRAFFIC_QUEUES field bits to 
> >> define which queue is scheduled. Only the set queues serves schedule 
> >> traffic. In this driver we set all 8 queues to be scheduled in 
> >> default, so all the traffic are schedule queues to schedule queue.
> >
> > I understand this, what I don't really understand is the distinction
> > that the switch makes between 'scheduled' and 'non-scheduled'
> > traffic.  What else does this distinction affect, apart from the
> > guard bands added implicitly here? The tc-taprio qdisc has no notion
> > of 'scheduled' queues, all queues are 'scheduled'. Do we ever need
> > to set the scheduled queues mask to something other than 0xff? If
> > so, when and why?
> 
> Yes, it seems only affect the guard band. If disabling always guard
> band bit, we can use SCH_TRAFFIC_QUEUES to determine which queue is
> non-scheduled queue. Only the non-scheduled queue traffic will reserve
> the guard band. But tc-taprio qdisc cannot set scheduled or
> non-scheduled queue now. Adding this feature can be discussed in
> future. 
> 
> It is not reasonable to add guardband in each queue traffic in
> default, so I disable the always guard band bit for TAS config.

Ok, if true, then it makes sense to disable ALWAYS_GUARD_BAND_SCH_Q.