[dpdk-users] scheduler issue

[Alex Kiselev]

On 2020-12-11 23:55, Singh, Jasvinder wrote:
>> On 11 Dec 2020, at 22:27, Alex Kiselev <alex at therouter.net> wrote:
>> 
>> On 2020-12-11 23:06, Singh, Jasvinder wrote:
>>>>> On 11 Dec 2020, at 21:29, Alex Kiselev <alex at therouter.net> wrote:
>>>> On 2020-12-08 14:24, Singh, Jasvinder wrote:
>>>>> <snip>
>>>>>> > [JS] now, returning to 1 mbps pipes situation, try reducing tc period
>>>>>> > first at subport and then at  pipe level, if that help in getting even
>>>>>> > traffic across low bandwidth pipes.
>>>>>> reducing subport tc from 10 to 5 period also solved the problem 
>>>>>> with 1
>>>>>> Mbit/s pipes.
>>>>>> so, my second problem has been solved,
>>>>>> but the first one with some of low bandwidth pipes stop 
>>>>>> transmitting still
>>>>>> remains.
>>>>> I see, try removing "pkt_len <= pipe_tc_ov_credits" condition in 
>>>>> the
>>>>> grinder_credits_check() code for oversubscription case, instead use
>>>>> this pkt_len <= pipe_tc_credits + pipe_tc_ov_credits;
>>>> if I do what you suggest, I will get this code
>>>>   enough_credits = (pkt_len <= subport_tb_credits) &&
>>>>       (pkt_len <= subport_tc_credits) &&
>>>>       (pkt_len <= pipe_tb_credits) &&
>>>>       (pkt_len <= pipe_tc_credits) &&
>>>>       (pkt_len <= pipe_tc_credits + pipe_tc_ov_credits);
>>>> And this doesn't make sense since if condition pkt_len <= 
>>>> pipe_tc_credits is true
>>>> then condition (pkt_len <= pipe_tc_credits + pipe_tc_ov_credits) is 
>>>> also always true.
>>> [JS] my suggestion is to remove“pkt_len <= pipe_tc_credits“, “ 
>>> pkt_len
>>> <= pipe_tc_ov_credits”and use only “pkt_len <= pipe_tc_credits +
>>> pipe_tc_ov_credits“
>>> While keeping tc_ov flag on.
>>>> Your suggestion just turns off TC_OV feature.
>> 
>> I don't see your point.
>> 
>> This new suggestion will also effectively turn off the TC_OV feature 
>> since
>> the only effect of enabling TC_OV is adding additional condition
>>  pkt_len <= pipe_tc_ov_credits
>> which doesn't allow a pipe to spend more resources than it should.
>> And in the case of support congestion a pipe should spent less than 
>> %100 of pipe's maximum rate.
>> 
>> And you suggest to allow pipe to spend 100% of it's rate plus some 
>> extra.
>> I guess effect of this would even more unfair support's bandwidth 
>> distibution.
>> 
>> Btw, a pipe might stop transmitting even when there is no congestion 
>> at a subport.
>> 
> Although I didn’t try this solution but the idea here is - in a
> particular round, of pkt_len is less than pipe_tc_credits( which is a
> constant value each time) but greater than pipe_tc_ov_credits, then it
> might hit the situation when no packet will be scheduled from the pipe
> even though there are fixed credits greater than packet size is
> available.

But that is a perfectly normal situation and that's exactly the idea 
behind TC_OV.
It means a pipe should wait for the next subport->tc_ov_period_id
when pipe_tc_ov_credits will be reset to a new value

   pipe->tc_ov_credits = subport->tc_ov_wm * params->tc_ov_weight;

which allows the pipe to continue transmitting.

And it could not cause a permanent pipe stop which is what I am facing.

> In fairness, pipe should send the as much as packets which
> consumes pipe_tc_credits, regardless of extra pipe_tc_ov_credits which
> is extra on top of pipe_tc_credits.

I think it's quite the opposite. That's why after I reduced the support 
tc_period
I got much more fairness. Since reducing subport tc_period also reduce 
the tc_ov_wm_max value.
	s->tc_ov_wm_max = rte_sched_time_ms_to_bytes(params->tc_period,
						     port->pipe_tc3_rate_max)
as a result a pipe transmits less bytes in one round. so pipe rotation 
inside a grinder
happens much more often and a pipe can't monopolise resources.

in other sos implementation this is called "quantum".

> 
> 
> 
> 
>> 
>>>>>> >
>>>>>> >
>>>>>> >
>>>>>> >>> rcv 0   rx rate 7324160 nb pkts 5722
>>>>>> >>> rcv 1   rx rate 7281920 nb pkts 5689
>>>>>> >>> rcv 2   rx rate 7226880 nb pkts 5646
>>>>>> >>> rcv 3   rx rate 7124480 nb pkts 5566
>>>>>> >>> rcv 4   rx rate 7324160 nb pkts 5722
>>>>>> >>> rcv 5   rx rate 7271680 nb pkts 5681
>>>>>> >>> rcv 6   rx rate 7188480 nb pkts 5616
>>>>>> >>> rcv 7   rx rate 7150080 nb pkts 5586
>>>>>> >>> rcv 8   rx rate 7328000 nb pkts 5725
>>>>>> >>> rcv 9   rx rate 7249920 nb pkts 5664
>>>>>> >>> rcv 10  rx rate 7188480 nb pkts 5616 rcv 11  rx rate 7179520 nb pkts
>>>>>> >>> 5609 rcv 12  rx rate 7324160 nb pkts 5722 rcv 13  rx rate 7208960 nb
>>>>>> >>> pkts 5632 rcv 14  rx rate 7152640 nb pkts 5588 rcv 15  rx rate
>>>>>> >>> 7127040 nb pkts 5568 rcv 16  rx rate 7303680 nb pkts 5706 ....
>>>>>> >>> rcv 587 rx rate 2406400 nb pkts 1880 rcv 588 rx rate 2406400 nb pkts
>>>>>> >>> 1880 rcv 589 rx rate 2406400 nb pkts 1880 rcv 590 rx rate 2406400 nb
>>>>>> >>> pkts 1880 rcv 591 rx rate 2406400 nb pkts 1880 rcv 592 rx rate
>>>>>> >>> 2398720 nb pkts 1874 rcv 593 rx rate 2400000 nb pkts 1875 rcv 594 rx
>>>>>> >>> rate 2400000 nb pkts 1875 rcv 595 rx rate 2400000 nb pkts 1875 rcv
>>>>>> >>> 596 rx rate 2401280 nb pkts 1876 rcv 597 rx rate 2401280 nb pkts
>>>>>> >>> 1876 rcv 598 rx rate 2401280 nb pkts 1876 rcv 599 rx rate 2402560 nb
>>>>>> >>> pkts 1877 rx rate sum 3156416000
>>>>>> >>
>>>>>> >>
>>>>>> >>
>>>>>> >>>>> ... despite that there is _NO_ congestion...
>>>>>> >>>>> congestion at the subport or pipe.
>>>>>> >>>>>> And the subport !! doesn't use about 42 mbit/s of available
>>>>>> >>>>>> bandwidth.
>>>>>> >>>>>> The only difference is those test configurations is TC of
>>>>>> >>>>>> generated traffic.
>>>>>> >>>>>> Test 1 uses TC 1 while test 2 uses TC 3 (which is use TC_OV
>>>>>> >>>>>> function).
>>>>>> >>>>>> So, enabling TC_OV changes the results dramatically.
>>>>>> >>>>>> ##
>>>>>> >>>>>> ## test1
>>>>>> >>>>>> ##
>>>>>> >>>>>> hqos add profile  7 rate    2 M size 1000000 tc period 40
>>>>>> >>>>>> # qos test port
>>>>>> >>>>>> hqos add port 1 rate 10 G mtu 1522 frame overhead 24 queue sizes
>>>>>> >>>>>> 64 64 64 64
>>>>>> >>>>>> hqos add port 1 subport 0 rate 300 M size 1000000 tc period 10
>>>>>> >>>>>> hqos add port 1 subport 0 pipes 2000 profile 7 hqos add port 1
>>>>>> >>>>>> subport 0 pipes 200 profile 23 hqos set port 1 lcore 3 port 1
>>>>>> >>>>>> subport rate 300 M number of tx flows 300 generator tx rate 1M TC
>>>>>> >>>>>> 1 ...
>>>>>> >>>>>> rcv 284 rx rate 995840  nb pkts 778 rcv 285 rx rate 995840  nb
>>>>>> >>>>>> pkts 778 rcv 286 rx rate 995840  nb pkts 778 rcv 287 rx rate
>>>>>> >>>>>> 995840  nb pkts 778 rcv 288 rx rate 995840  nb pkts 778 rcv 289
>>>>>> >>>>>> rx rate 995840  nb pkts 778 rcv 290 rx rate 995840  nb pkts 778
>>>>>> >>>>>> rcv 291 rx rate 995840  nb pkts 778 rcv 292 rx rate 995840  nb
>>>>>> >>>>>> pkts 778 rcv 293 rx rate 995840  nb pkts 778 rcv 294 rx rate
>>>>>> >>>>>> 995840  nb pkts 778 ...
>>>>>> >>>>>> sum pipe's rx rate is 298 494 720 OK.
>>>>>> >>>>>> The subport rate is equally distributed to 300 pipes.
>>>>>> >>>>>> ##
>>>>>> >>>>>> ##  test 2
>>>>>> >>>>>> ##
>>>>>> >>>>>> hqos add profile  7 rate    2 M size 1000000 tc period 40
>>>>>> >>>>>> # qos test port
>>>>>> >>>>>> hqos add port 1 rate 10 G mtu 1522 frame overhead 24 queue sizes
>>>>>> >>>>>> 64 64 64 64
>>>>>> >>>>>> hqos add port 1 subport 0 rate 300 M size 1000000 tc period 10
>>>>>> >>>>>> hqos add port 1 subport 0 pipes 2000 profile 7 hqos add port 1
>>>>>> >>>>>> subport 0 pipes 200 profile 23 hqos set port 1 lcore 3 port 1
>>>>>> >>>>>> subport rate 300 M number of tx flows 300 generator tx rate 1M TC
>>>>>> >>>>>> 3
>>>>>> >>>>>> h5 ~ # rcli sh qos rcv
>>>>>> >>>>>> rcv 0   rx rate 875520  nb pkts 684
>>>>>> >>>>>> rcv 1   rx rate 856320  nb pkts 669
>>>>>> >>>>>> rcv 2   rx rate 849920  nb pkts 664
>>>>>> >>>>>> rcv 3   rx rate 853760  nb pkts 667
>>>>>> >>>>>> rcv 4   rx rate 867840  nb pkts 678
>>>>>> >>>>>> rcv 5   rx rate 844800  nb pkts 660
>>>>>> >>>>>> rcv 6   rx rate 852480  nb pkts 666
>>>>>> >>>>>> rcv 7   rx rate 855040  nb pkts 668
>>>>>> >>>>>> rcv 8   rx rate 865280  nb pkts 676
>>>>>> >>>>>> rcv 9   rx rate 846080  nb pkts 661
>>>>>> >>>>>> rcv 10  rx rate 858880  nb pkts 671 rcv 11  rx rate 870400  nb
>>>>>> >>>>>> pkts 680 rcv 12  rx rate 864000  nb pkts 675 rcv 13  rx rate
>>>>>> >>>>>> 852480  nb pkts 666 rcv 14  rx rate 855040  nb pkts 668 rcv 15
>>>>>> >>>>>> rx rate 857600  nb pkts 670 rcv 16  rx rate 864000  nb pkts 675
>>>>>> >>>>>> rcv 17  rx rate 866560  nb pkts 677 rcv 18  rx rate 865280  nb
>>>>>> >>>>>> pkts 676 rcv 19  rx rate 858880  nb pkts 671 rcv 20  rx rate
>>>>>> >>>>>> 856320  nb pkts 669 rcv 21  rx rate 864000  nb pkts 675 rcv 22
>>>>>> >>>>>> rx rate 869120  nb pkts 679 rcv 23  rx rate 856320  nb pkts 669
>>>>>> >>>>>> rcv 24  rx rate 862720  nb pkts 674 rcv 25  rx rate 865280  nb
>>>>>> >>>>>> pkts 676 rcv 26  rx rate 867840  nb pkts 678 rcv 27  rx rate
>>>>>> >>>>>> 870400  nb pkts 680 rcv 28  rx rate 860160  nb pkts 672 rcv 29
>>>>>> >>>>>> rx rate 870400  nb pkts 680 rcv 30  rx rate 869120  nb pkts 679
>>>>>> >>>>>> rcv 31  rx rate 870400  nb pkts 680 rcv 32  rx rate 858880  nb
>>>>>> >>>>>> pkts 671 rcv 33  rx rate 858880  nb pkts 671 rcv 34  rx rate
>>>>>> >>>>>> 852480  nb pkts 666 rcv 35  rx rate 874240  nb pkts 683 rcv 36
>>>>>> >>>>>> rx rate 855040  nb pkts 668 rcv 37  rx rate 853760  nb pkts 667
>>>>>> >>>>>> rcv 38  rx rate 869120  nb pkts 679 rcv 39  rx rate 885760  nb
>>>>>> >>>>>> pkts 692 rcv 40  rx rate 861440  nb pkts 673 rcv 41  rx rate
>>>>>> >>>>>> 852480  nb pkts 666 rcv 42  rx rate 871680  nb pkts 681 ...
>>>>>> >>>>>> ...
>>>>>> >>>>>> rcv 288 rx rate 766720  nb pkts 599 rcv 289 rx rate 766720  nb
>>>>>> >>>>>> pkts 599 rcv 290 rx rate 766720  nb pkts 599 rcv 291 rx rate
>>>>>> >>>>>> 766720  nb pkts 599 rcv 292 rx rate 762880  nb pkts 596 rcv 293
>>>>>> >>>>>> rx rate 762880  nb pkts 596 rcv 294 rx rate 762880  nb pkts 596
>>>>>> >>>>>> rcv 295 rx rate 760320  nb pkts 594 rcv 296 rx rate 604160  nb
>>>>>> >>>>>> pkts 472 rcv 297 rx rate 604160  nb pkts 472 rcv 298 rx rate
>>>>>> >>>>>> 604160  nb pkts 472 rcv 299 rx rate 604160  nb pkts 472 rx rate
>>>>>> >>>>>> sum 258839040 FAILED.
>>>>>> >>>>>> The subport rate is distributed NOT equally between 300 pipes.
>>>>>> >>>>>> Some subport bandwith (about 42) is not being used!