[LITMUS^RT] Running LITMUS-RT on ARM64

[Björn Brandenburg]

> 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?

- Björn