[LITMUS^RT] question about rtspin -- Sisu

[Sisu Xi]

Hi, Björn:

Thanks very much for the reply!

Sisu


On Thu, Jul 3, 2014 at 3:48 AM, Björn Brandenburg <bbb at mpi-sws.org> wrote:

>
> On 03 Jul 2014, at 08:08, Sisu Xi <xisisu at gmail.com> wrote:
> >
> > Previously (about 1 year ago), when I run litmus^RT in a VM and test
> with rtspin. the workload would actually scale according to the CPU
> resources allocated to the VM.
> > For example, if set the cap of a VM to 50%, and run a rtspin with 50%
> utilization, it becomes 25%.
>
> This is certainly not intended or supported behavior.
>
> >
> > But right now I updated litmus to the current version and that problem
> seems gone. Has anyone else experienced the same problem?
>
> No, I haven’t heard of this before.
>
> > Just want to send this email to confirm with you, does rtspin works fine
> in a virtualized environment as well?
>
> We don’t run LITMUS^RT in a VM environment, so I don’t know for sure.
> There are no fundamental reasons as to why it should not work.
>
> rtspin uses the kernel’s notion of “execution time” to determine when to
> cease spinning, i.e., each job spins until the kernel claims that the job
> has consumed a certain amount of CPU time. The code of rtspin itself has
> not changed, so if you are seeing different behavior, then this indicates
> that the kernel has a different notion of “time spent executing” in a VM in
> newer kernel versions. This is not something that we changed, but may be
> due to the newer base kernel version. You would have to dig into how the
> kernel’s timekeeping implementation works when it is virtualized.
>
> > Also, Is it recommended to use rtspin for synthetic workload experiment?
>
> No. rtspin is a debugging helper.
>
> Regards,
> Björn
>
>
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>



-- 


*Sisu Xi, PhD Candidate*

http://www.cse.wustl.edu/~xis/
Department of Computer Science and Engineering
Campus Box 1045
Washington University in St. Louis
One Brookings Drive
St. Louis, MO 63130
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