Re: RT-Xen on ARM

[Andrii Anisov <andrii_anisov@epam.com>]

Hello,


On 27.09.17 22:57, Meng Xu wrote:
> Note that:
> When you use gEDF scheduler in VM or VMM (i.e., Xen), you should use
> MPR2 model
I guess you mean DMPR in CARTS terms.

>   to compute the resource interface (i.e., VCPU parameters).
> When you use pEDF scheduler, you should use PRM model to compute.
>>      - Could you please provide an example input xml for CARTS described a
>> system with 2 RT domains with 2 VCPUs each, running on a 2PCPUs, with gEDF
>> scheduling at VMM level (for XEN based setup).
> Hmm, if you use the gEDF scheduling algorithm, this may not be
> possible. Let me explain why.
> In the MPR2 model, it computes the interface with the minimum number
> of cores. To get 2 VCPUs for a VM, the total utilization (i.e., budget
> / period) of these two VCPUs must be larger than 1.0. Since you ask
> for 2 domains, the total utilization of these 4 VCPUs will be larger
> than 2.0, which are definitely not schedulable on two cores.
Well, if we are speaking about test-cases similar to described in [1], 
where the whole real time tasks set utilization is taken from 
1.1...(PCPU*1)-0.1, there is no problem with having VCPU number greater 
than PCPUs. For sure if we take number of domains  more that 1.

> If you are considering VCPUs with very low utilization, you may use
> PRM model to compute each VCPU's parameters; after that, you can treat
> these VCPUs as tasks, create another xml file, and ask CARTS to
> compute the resource interface for these VCPUs.
Sounds terrible for getting it scripted :(
> (Unfortunately, the current CARTS implementation does not support
> mixing MPR model in one XML file, although it is supported in theory.
> This can be worked around by using the above approach.)
>
>> For pEDF at both VMM and
>> domain level, my understanding is that the os_scheduler represents XEN, and
>> VCPUs are represented by components with tasks running on them.
> Yes, if you analyze the entire system that uses one type of scheduler
> with only one type of model (i.e., PRM or MPR2).
>
> If you mixed the scheduling algorithm or the interface model, you can
> compute each VM or VCPU's parameters first. Then you treat VCPUs as
> tasks and create another XML which will be used to compute the number
> of cores to schedule all these VCPUs.
>
>>      - I did not get a concept of min_period/max_period for a
>> component/os_scheduler in CARTS description files. If I have them different,
>> CARTS gives calculation for all periods in between, but did not provide the
>> best period to get system schedulable.
> You should set them to the same value.
Ok, how to chose the value for some taskset in a component?

-- 

*Andrii Anisov*



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