Re: [PATCH 0 of 3] RFC: creating a particular vcpu type

[Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Hollis Blanchard wrote:
> If it's the "ioctl" in the function name you object to, that's easily
> changed.
>   

It's not the name, it's what you're doing.  You're introducing an 
architecture specific ioctl that essentially overrides an 
common-ioctl().  If anything, I would think it would be better to expand 
the existing common-ioctl with the notion and then have a 
per-architecture hook within that ioctl.

> I think it's reasonable to say that single-system-image software
> requires identical cores, but that's not what we're talking about here.
> Heterogeneous core designs are not common, but a VM needs to reflect
> hardware layout, and people do it in hardware (again, not running a
> single system image).
>
> "VCPU type" is a VCPU property, and I think the design should reflect
> that, and as you can see from the patch it's not at all difficult to do.
>   

There are all sorts of crazy things you can do in actual hardware.  Look 
at the way the cell processor handles memory for SPUs.  You would need 
to change the KVM memory code to have per-CPU slots or something to 
support that.

We shouldn't design for any possible thing that anyone could want in the 
future, but rather for the things that we actually can see doing.

If you don't think there's a reasonable chance that you'll be attempting 
to implement asymmetric cores in the near future, I wouldn't think it's 
wise to over complicate things.

Regards,

Anthony Liguori


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