netdev - Re: [PATCH iproute2-next] taprio: Add support for the SetAndHold and SetAndRelease commands

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Message-ID: <076a012b-a699-abac-ca04-56201036fb1d@ti.com>
Date:   Fri, 17 Jan 2020 17:18:07 -0500
From:   Murali Karicheri <m-karicheri2@...com>
To:     Jose Abreu <Jose.Abreu@...opsys.com>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Joao Pinto <Joao.Pinto@...opsys.com>,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH iproute2-next] taprio: Add support for the SetAndHold and
 SetAndRelease commands

Hi Jose,

On 01/07/2020 04:27 AM, Jose Abreu wrote:
> From: Murali Karicheri <m-karicheri2@...com>
> Date: Jan/03/2020, 22:24:14
> (UTC+00:00)
> 
>> So you have one sched entry that specify SetAndHold for all remaining
>> queues. So this means, queue 0 will never get sent. I guess you also
>> support SetAndRelease so that a mix of SetAndHold followed by
>> SetAndRelease can be sent to enable sending from Queue 0. Is that
>> correct?
>>
>> Something like
>>                 sched-entry H 02 300000 \ <=== 300 usec tx from Q1
>>                 sched-entry R 01 200000   <=== 300 usec tx from Q0
>>
>> Just trying to understand how this is being used for real world
>> application.
> 
> This is the command I use:
> 
> # tc qdisc add dev $intf handle 100: parent root taprio \
> 	num_tc 4 \
> 	map 0 1 2 3 3 3 3 3 3 3 3 3 3 3 3 3 \
> 	base-time $base \
> 	cycle-time 1000000 \
> 	sched-entry R 00 100000 \
> 	sched-entry H 02 200000 \
> 	sched-entry H 04 300000 \
> 	sched-entry H 08 400000 \
> 	flags 0x2
> # sleep 2
> # iperf3 -c <ip> -u -b 0 -t 15 &
> # sleep 5
> # echo "Queue 3: Expected=40%, Queue 0 will now be preempted"
> # tperf -i <ethX> -p 3
> 
> This will basically preempt Queue 0 and flood Queue 3 with express
> traffic.
I see you don't include Q0 in your schedule. Why is that the case?

Why is the entry with zero mask introduced (first entry)? Typo?
I thought it should be like below. No?

 > # tc qdisc add dev $intf handle 100: parent root taprio \
 > 	num_tc 4 \
 > 	map 0 1 2 3 3 3 3 3 3 3 3 3 3 3 3 3 \
 > 	base-time $base \
 > 	cycle-time 1000000 \
 > 	sched-entry R 01 100000 \
 > 	sched-entry H 02 200000 \
 > 	sched-entry H 04 300000 \
 > 	sched-entry H 08 400000 \
 > 	flags 0x2

Based on my understanding, if holdAdvance is t1 and releaseAdvance is
t2, hold is asserted t1 nano second before Q1 slot (during first
entry) begins and release is asserted t2 nano second before the start of
Q0 slot (during fourth entry) so that pre-emptable frame start 
transmission during first entry.

I thought R/H entries are a replacement for zero mask entry that
are introduced in the schedule as a guard band before express queue
slot when frame pre-emption not supported. Is my understanding correct?

So the above make sense?

Regards,

Murali
> 
> You can find tperf utility here: https://github.com/joabreu/tperf
> 
> ---
> Thanks,
> Jose Miguel Abreu
> 

-- 
Murali Karicheri
Texas Instruments