Re: [Xen-devel] [RFC] Shared coprocessor framework

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

Stefano,

Please see my answers below:
>
> Thank you for the document, I think is a very good start. I also see the
> need for this framework. Please add more details about the proposed
> interface (Xen API, hypercalls, etc) in the next version; I am looking
> forward to it.

We will come up with the document update once we have it agreed internally.

>> AA> Due to the fact that some domain assigned a vcoproc could access coproc 
>> when
>> AA> it is running another domain context, framework will implement iomem 
>> access
>> AA> emulation for domains which are not provided coproc at the moment of 
>> access.
>
> This is certainly going to be the hardest part. I take the framework is
> just going to provide a generic API for implementing a coprocessor
> emulator and it is going to be up to each coprocessor implementation to
> provide the code.

This piece together with the context switching logic is definitely a
platform specific stuff and its complexity could be different
coprocessor to coprocessor.
Registers access emultaion for not running vcopro is expected to be
not very complex for our case:
    - saved context return on register read
    - stacking on writes to be executed during switching context to that vcoproc
    - rare more complex corner cases

> Is the emulator going to live in the Xen hypervisor?
That is the idea.

> It would be nice to provide a simple coprocessor example, if you have one.
I'm not really sure about a simple functional example. We are
targeting GPU sharing for the first drop.

Sincerely,
Andrii Anisov.

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