[LITMUS^RT] Running LITMUS-RT on ARM64

[Meng Xu]

On Tue, Aug 29, 2017 at 10:26 AM, Björn Brandenburg <bbb at mpi-sws.org> wrote:

>
> > On 29. Aug 2017, at 16:23, Meng Xu <xumengpanda at gmail.com> wrote:
> >
> >>> 3) It’s not just rtspin that will be confused — likely all of
> LITMUS^RT’s
> >>> budget tracking and enforcement code will not work as expected under
> >>> virtualization (when given vCPUs with non-100% utilization). This is
> because
> >>> the scheduler is not aware of any times during which a vCPU does not
> receive
> >>> service, so tasks will be charged for bogus execution time.
> >>
> >> This sounds really bad.
> >
> > I'm wondering if it's designed for this on purpose by Linux people?
> > If yes, they must have discussed some tradeoffs; otherwise, it could
> > lead to some issues.
>
> What is the alternative? The guest kernel does not know when the vCPU is
> actually making progress. So how could it react in any other way? Or is
> there some interface exported by Xen that would allow us to infer exactly
> how much service a vCPU received?
>

​When a VCPU is preempted, it notify the guest kernel; when a VCPU resumes,
it notify the guest kernel. Then the guest kernel knows how long the vcpu
is preempted.
​I'm unaware this interface has been implemented in Xen or not. But I think
it's doable.​

​(I'm thinking in research perspective. If this issue is serious enough, I
guess it could be a research problem to look at)​

Best,

Meng​

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