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 11:26:32 +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 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?