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From:   Xiaoliang Yang <xiaoliang.yang_1@nxp.com>
To:     Vladimir Oltean <olteanv@gmail.com>
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Subject: RE: [EXT] Re: [net-next] net: dsa: felix: disable always guard band
 bit for TAS config
Thread-Topic: [EXT] Re: [net-next] net: dsa: felix: disable always guard band
 bit for TAS config
Thread-Index: AQHXNQV6cbEkHp2uw0G0oLH1EhbdIaq7x7yAgADvIJCAAFzVAIAAAeSw
Date:   Tue, 20 Apr 2021 10:28:45 +0000
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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=20
>> >the port, why are some queues scheduled and some not?
>>
>> The felix vsc9959 device can set SCH_TRAFFIC_QUEUES field bits to=20
>> define which queue is scheduled. Only the set queues serves schedule=20
>> traffic. In this driver we set all 8 queues to be scheduled in=20
>> 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 bi=
t, 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. Bu=
t tc-taprio qdisc cannot set scheduled or non-scheduled queue now. Adding t=
his feature can be discussed in future.=20

It is not reasonable to add guardband in each queue traffic in default, so =
I disable the always guard band bit for TAS config.

Thanks,
Xiaoliang Yang