[LITMUS^RT] Running LITMUS-RT on ARM64

[Meng Xu]

On Tue, Aug 29, 2017 at 10:56 AM, Björn Brandenburg <bbb at mpi-sws.org> wrote:

>
> > On 29. Aug 2017, at 16:45, Meng Xu <xumengpanda at gmail.com> wrote:
> >
> > 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 agree that it’s definitely doable in a para-virtualization setting with
> a cooperative guest kernel, and I’d bet something similar has been done in
> the context of the lock-holder preemption problem.
>
> It’s less obvious to me how one would solve this under full/native
> virtualization, where the guest OS is blissfully unaware of the fact that
> it is being virtualized without 100% CPU capacity.
>
> > ​(I'm thinking in research perspective. If this issue is serious enough,
> I guess it could be a research problem to look at)​
>
> Let me know if you end up working on this and need a collaborator. ;-)
>

​Sure! I need to do some survey about this first. :)

Best,

​Meng​

​


>
> - Björn
>
>


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