Re: [Xenomai] Virtualization with Xenomai

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2013-08-30 09:11, Asier wrote:
> Jan, Nicolas,
> 
> Thank you for your help:
> 
>> Third option may be even more interesting (provided you really want to
>> use Windows for the UI): Run Xenomai on the host and combine it with KVM
>> to host another OS. This works fine with latest ipipe for 3.8 when RT
>> tasks and the QEMU process (that uses KVM) are on separate CPUs, I just
>> heard of issues (couldn't reproduce yet) when they share a CPU.
>>
> If I am not wrong, KVM runs on top of Linux, and then Windows on top of it.
> Isn't it too much overhead? Isn't it better to use a Type 1 virtualization?

Type 1 vs. type 2 is usually just marketing nonsense. You can do device
pass-through with KVM as well, thus removing most of the I/O
virtualization overhead, achieving near-native performance. Moreover, in
contrast to several other hypervisors, KVM can benefit a lot from its
architectural advantage to run hosted on Linux which reduced context
switches on x86.

> When you say separate CPUs, do you mean separate cores?

Usually, this means cores (on a single-socket system).

> 
>> Virtualizing your RT workload won't make things faster, naturally.
>> Depending on the hypervisor architecture and hardware capabilities, it
>> may not be measurable.
>>
> So, do you mean that, even though the system may be slower, the real-time
> response will run smoothly?

No general rule, depends on your hypervisor.

> 
>> But I would refrain from such stacking unless there is a real need
>> (which I do not see for your setup).
>>
> My plan for the mid term is to run the user interface (HMI) and the
> real-time applications in one board. Meanwhile, I need to update my HMI and
> I want to use a complete Linux distribution (one with a desktop manager)
> with Xenomai. However, I may finally be forced to use Windows (3rd party
> programs) and, when porting my system to one board, I would need some
> virtualization tools.
> 
> Yesterday, I wrote another e-mail asking for opinions about a Linux
> distribution with Xenomai, or about any experience with the Yocto project
> and Xenomai. Has anyone got any information regarding this?

There are debian packages for Xenomai, but it is trivial to build it for
any distro of your preference. Yocto-wise: ELDK, which should come with
Xenomai support IIRC, is based on yocto these days.

Jan

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