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

On Thu, 2017-09-28 at 18:01 +0200, Dario Faggioli wrote:
> On Thu, 2017-09-28 at 12:18 +0300, Andrii Anisov wrote:
> > > > 
> The GP scheduler --like Credit1 or Credit2, if you are on Xen-- will
> give you fairness, but without any precise temporal guarantee. This
> means that, in this case, each vCPU will be given the chance to run
> for
> 1/2 CPU capacity (at there are 2 CPUs, 4 vCPUs total, i.e., 2/4=1/2).
> You can influence this with weights, but that's still "not real-
> time".
> I.e., if you say that d1v0 and d1v1 have double the weights of d2v0
> and
> d2v1, if 2 is the total available CPU capacity, d1's vCPUs will run
> for
Err... Sorry, I hit send, before finishing this paragraph.

I meant to say: if you set d1 to have twice as much the weight of d2
(because weights, in Credit1 and Credit2, are set on a per-domain
basis), d1 will execute for about ~130% of CPU time (subdivided,
theoretically equally, between d1v0 and d1v1), and d2 will execute for
~70% (subdivided between d2v0 and d2v1).

So, basically, the 2x ratio between the domain's execution time is
achievable, with a general purpose scheduler, but it's not possible to
specify, and have it enforced, any time granularity. 

<<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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