Re: RT-Xen on ARM

[Meng Xu <xumengpanda@gmail.com>]

On Wed, Sep 27, 2017 at 10:37 AM, Andrii Anisov <andrii_anisov@epam.com> wrote:
> Hello,
>
>
> On 27.09.17 16:57, Meng Xu wrote:
>>
>> The command is:
>> java -jar carts.jar inputfile outputfile
>
> From the next example, I would say the command is:
>     java -jar carts.jar inputfile interface_type outputfile
>
>> An example command is:
>> java -jar carts.jar 1-1.10-in.xml MPR2 1-1.10-out.xml
>
> Thanks a lot. It does work.
>
> Could you please clarify a bit more points to me:
>     - As I understand the upstreamed rtds employs gEDF only. Is it correct?

RTDS can support gEDF and partitioned EDF.
To support pEDF, you can set each VCPU's affinity (hard and soft
affninity)  to only one core using "xl vcpu-pin" command. The VCPUs on
each core will be scheduled by pEDF scheduling algorithm.

Note that:
When you use gEDF scheduler in VM or VMM (i.e., Xen), you should use
MPR2 model 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.

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.

(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.
min_period/max_period range is used for other models. I never used it.

Best,

Meng

-- 
Meng Xu
Ph.D. Candidate in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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