Re: [Xen-devel] [DOC RFC] Heterogeneous Multi Processing Support in Xen

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Thu, 2016-12-08 at 03:14 -0700, Jan Beulich wrote:
> > > > On 07.12.16 at 19:29, <dario.faggioli@xxxxxxxxxx> wrote:
> > The list of classes is kept ordered from the more powerful to the
> > less
> > powerful.
> > **TODO:** this has been [proposed by 
> > George](https://lists.xenproject.org/archives/html/xen-devel/2016-0
> > 9/msg02212.html).
> > I like the idea, what do others think? If we agree on that, note
> > that there
> > has been no discussion on defining what "more powerful" means,
> > neither on
> > x86 (although, not really that interesting, for now, I'd say), nor
> > on ARM.
> 
> Indeed I think there should be no assumption about the ability to
> order things here: Even if for some initial set of hardware it may
> be possible to clearly tell which one's more powerful and which
> one's more weak, already the moment you extend this from
> compute power to different ISA extensions you'll immediately end
> up with the possibility of two CPUs have a distinct extra feature
> compared to one another (say one a crypto extension and the
> other a wider vector compute engine).
> 
Yeah, that was what was puzzling me too. Keeping them ordered has the
nice property that if a user says the following in a config file:

 vcpuclass=["0-3:class0", "4-7:class1"]

(assuming that class0 and class1 are the always available Xen names) it
would be always true that vCPUs 0-3 are 'more powerful', no matter on
what host the VM runs (ARM and x86, now and in 5 years, etc), which
would be really nice.

But I really am not sure whether that is possible.

Perhaps George, which thought about this first, has it more clear...

Thanks and Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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