The design of vCPU.

Philipp Eppelt philipp.eppelt at
Thu Jun 12 10:00:24 UTC 2014


I think we have to chose the 'host model'. In order to provide
separation POK puts (at least some) device drivers (network card) into
their own partitions and offers a kernel supervised communication
interface. (If this is new, read the POK paper by Julien.)

This also implies some restrictions on the device driver used. They need
to be implemented in POK and the RTEMS guest needs to communicate with
these drivers.

It looks unlikely to me, that we are able to assign hardware exclusively
to one partition. Also this needs to be configurable through the AADL
model at some point in time.

Concerning the vCPU research you did:

For now, it is sufficient to support just one vCPU on a single core
processor. No SMP, no mixed design with more than one vCPUs or a vCPU
and a native partition.
You should keep this in mind to ease future development, which works on
these issues, but it is not your concern right now.

This brings me to you scheduling issue. A vCPU is basically a task in
POK. This task is scheduled like any other task from the kernel point of
view. What this task does internally is of no concern to the kernel.
So the vCPU is just a partition to POK.

How to get a unique ID for the vCPU? Reuse the partition ID, POK already

The interrupt delivery mechanism is still an open question, but I like
to focus on a simple hello world. This doesn't need interrupts outside
the kernel. It is a proof-of-concept for your VMM and vCPU.
It also raises the question of loading a guest binary.
But this also looks like beyond midterm.

To summarize:
* host model
* small, simple vCPU model, without own scheduling policies and without SMP
* vCPU needs to look like a partition to the kernel
* no interrupts for now!

Figure out, which parts of the vCPU and VMM need to go where in the POK
system. Meaning, what needs to go to kernel/* and what to libpok/* and
where does it belong in there.


On 06/10/2014 04:25 PM, Youren Shen wrote:
> Hi, Philipp:
> As I said in the last post, there are still several issues remained to
> be discussed. I hope I can have a discussion with you in some
> day.According to the discussion in the meeting, we need to figure out a
> realistic target for midterm.
> I have post a blog about the pictures that I want to share and discuss
> with you.
> Thank you very much.
> [1].
> On Tue, Jun 10, 2014 at 7:13 PM, Youren Shen <shenyouren at
> <mailto:shenyouren at>> wrote:
>     Hi,Philipp:
>     Sorry for so late to update my blog, I got two examinations last
>     Sunday, so I have to prepare it in Saturday.
>     I have post a blog[1] about my design of vCPU. please have a review.
>     I have described several problem and their solutions, if you have
>     any suggestion, please tell me.
>     I will update another blog later, for the interesting picture I
>     mentioned before.
>     Thank you very much.
>     [1].
>     -- 
>     Best Regards.
>     Youren Shen.
> -- 
> Best Regards.
> Youren Shen.

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