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Re: [Xen-devel] xen 4.5.0 rtds scheduler perform poorly with 2vms

Hi Meng,

Thank you so much for being this patience.

So a task set is composed of a collection of real-time tasks, and each real-time task is a sequence of jobs that are released periodically... All jobs are periodic, where each job Ti is defined by a period (and deadline) pi and a worse-case execution time ei, with pi â ei â 0 and pi, ei â integers. Each job is comprised of a number of iterations of floating point operations during each job. This is based on the base task.c provided with the LITMUSRT userspace library.

So in a tasks set, there are many tasks, and in each tasks, there are a sequence of jobs, if any job misses deadline, then the whole taskset is qualified as failed to be schedulable.Â

Thank you


On Fri, Nov 27, 2015 at 4:17 PM, Meng Xu <xumengpanda@xxxxxxxxx> wrote:
2015-11-27 14:50 GMT-05:00 Yu-An(Victor) Chen <chen116@xxxxxxx>:
> Hi Dario & Meng,
> Thanks for your analysis!
> VM1 and VM2 both are given 8 vCPUs and sharing physical CPU 0-7. So in
> theory,"VM1 can get the services of 400%"
> And yes, Dario, your explanation about the task utilization is correct.
> So the resource configuration as I mentioned before is:
> for xen-credit : 2vms (both vm are given 8 vCPUs) sharing 8 cores (cpu 0-7)
> using credit scheduler(both with weight of 800 and capacity of 400)
> for xen-rtds: 2 vms (both vm are given 8 vCPUs) sharing 8 cores (cpu0-7)
> using RTDS (both with period of 10000 and budget of 5000)
> In both setup, dom0 is using 1 core from cpu 8-15
> In both setup:
> I loaded VM2 with constant running task with total utilization of 4 cores.
> and in VM1 I run iterations of tasks of total utilization rate of 1 cores, 2
> cores, 3 cores, 4 cores, and then record their schedulbility.
> Attached is the result plot.
> I have tried with the newest litmust-rt, and rtxen is still performing
> poorly.

What is the characteristics of tasks you generated? When a taskset
miss ddl., which task inside miss deadline?


> Thank you both very much again, if there is any unclear part, please lemme
> know, thx!
> Victor
> On Fri, Nov 27, 2015 at 9:41 AM, Meng Xu <xumengpanda@xxxxxxxxx> wrote:
>> 2015-11-27 12:23 GMT-05:00 Dario Faggioli <dario.faggioli@xxxxxxxxxx>:
>> > On Fri, 2015-11-27 at 08:36 -0800, Yu-An(Victor) Chen wrote:
>> >> Hi Dario,
>> >>
>> > Hi,
>> >
>> >> Thanks for the reply!
>> >>
>> > You're welcome. :-)
>> >
>> > I'm adding Meng to Cc...
>> >
>> Thanks! :-)
>> >> My goal for the experiment is to show that xen rtds scheduler is
>> >> better than credit scheduler when it comes to real time tasks.
>> >> so my set up is:
>> >>
>> >> for xen-credit : 2vms sharing 8 cores (cpu 0-7) using credit
>> >> scheduler(both with weight of 800 and capacity of 400)
>> So you set up 400% cpu cap for each VM. In other words, each VM will
>> have computation capacity almost equal to 4 cores. Because VCPUs are
>> also scheduled, the four-core capacity is not equal to 4 physical core
>> in bare metal, because the resource supplied to tasks from VCPUs also
>> depend on the scheduling pattern (which affect the resource supply
>> pattern) of the VCPUs.
>> >> for xen-rtds: 2 vms sharing 8 cores (cpu0-7) using RTDS (both with
>> >> period of 10000 and budget of 5000)
>> How many VCPUs for each VM? If each VM has 4 VCPU, each VM has only
>> 200% CPU capacity, which is only half compared to the configuration
>> you made for credit scheduler.
>> >> in both setup, dom0 is using 1 core from cpu 8-15
>> Do you have some quick evaluation report (similar to the evaluation
>> section in academic papers) that describe how you did the experiments,
>> so that we can have a better guess on where goes wrong.
>> Right now, I'm guessing that: the resource configured for each VM
>> under credit and rtds schedulers are not the same, and it is possible
>> that some parameters are not configured correctly.
>> Another thing is that:
>> credit scheduler is work conserving, while RTDS is not.
>> So under the under-loaded situation, you will see credit scheduler may
>> work better because it try to use as much resource as it could. You
>> can make the comparision more failrly by setting the cap for credit
>> scheduler as you did, and running some background VM or tasks to
>> consume the idle resource.
>> Meng


Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania

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