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Re: [Xen-devel] [PATCH v1 1/4] xen: add real time scheduler rt

2014-09-04 10:27 GMT-04:00 Dario Faggioli <dario.faggioli@xxxxxxxxxx>:
On mer, 2014-09-03 at 18:18 +0100, George Dunlap wrote:
> On Wed, Sep 3, 2014 at 5:57 PM, Dario Faggioli
> <dario.faggioli@xxxxxxxxxx> wrote:

> > For instance, I can put, in an SMP guest, two real-time applications
> > with different timing requirements, and pin each one to a different
> > (v)cpu (I mean pin *inside* the guest). At this point, I'd like for each
> > vcpu to have a set of RT scheduling parameters, at the Xen level, that
> > matches the timing requirements of what's running inside.
> >
> > This may not look so typical in a server/cloud environment, but can
> > happen (at least in my experience) in a mobile/embedded env.
> But to play devil's advocate for a minute here:
Hehe, please, be my guest! :-D :-D

> couldn't you just put
> them in two different single-vcpu VMs then?

âWell, let me give a simpler example:
Suppose we have three tasks in one VM, each task has period 4ms and budget â6ms (its utilization is 2/3). If all these three tasks starts execution at the same time, we can use two full-capacity vcpus (200% capacity cpu resource) to schedule these three tasks.Â
However if you want to get two VMs, each of which has a full capacity vcpu (100% capacity cpu), we cannot schedule these three tasks, because one tasks cannot (well, at least very hard) migrate from one VM to another.Â

âThis is just a simple example, we could of course have an example like this but the vcpus are not full-capacity vcpus. :-)


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