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Re: [Xen-devel] RT-Xen on ARM

On Mon, 2017-07-03 at 14:42 -0400, Meng Xu wrote:
> On Mon, Jul 3, 2017 at 10:58 AM, Andrii Anisov <andrii_anisov@xxxxxxx
> m> wrote:
> > 
> Once the scheduling policy is determined, you will need to configure
> the VCPUs' parameters based on the systems' workload.
> This requires the workload's timing parameters for the CARTS tool to
> compute the VCPUs' parameters.
Yes, this is an interesting thing that Meng is mentioning.

RTDS allows you to specify the parameters (budget and period, or,
depending on how you prefer to see things, utilization and latency) on
a per-vCPU basis.

This may look cumbersome and overly complicated (and, in fact, if you
don't need it, you can ignore it :-D), but it may actually be really
important in a truly RT scenario.

Whether or not it is useful, almost entirely depends on what the VM is
doing, and how you decide to control and configure things inside it.
For example, if you have a particular task in the VM that you need must
absolutely execute for at least 10ms every 100ms, you can:
- inside the VM, pin the task to vCPU 0, and give it top priority;
- at the Xen level, give (with RTDS) to vCPU 0 budget=10ms and 
  period=100ms (or maybe budget of 12ms, to allow for some overhead

This is something that no other scheduler allows you to do. :-)

<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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