[libvirt] CPU Support

[Pavel Hrdina]

On Wed, Jul 18, 2018 at 10:50:34AM +0100, Daniel P. Berrangé wrote:
> On Wed, Jul 18, 2018 at 12:41:48PM +0300, Hetz Ben Hamo wrote:
> > Hi,
> > 
> > I've been looking at the CPU list and although I see lots of CPU's, I
> > cannot find 2 CPU families:
> > 
> > * AMD Ryzen
> > * AMD Threadripper
> > 
> > Although EPYC has been added recently.
> > 
> > Are there any missing details which preventing adding those CPU's to the
> > list?
> 
> Libvirt adds CPU models based on what QEMU supports. So from libvirt side the
> answer is simply that QEMU doesn't expose any models for Ryzen/Threadripper,
> but I'm not clear why it doesn't...
> 
> For a while I thought Ryzen/Threadripper would have same feature set as
> EPYC, but I've seen bugs recently suggesting that is not in fact the
> case. So it does look like having those models exposed by QEMU might
> be useful.
> 
> Copy'ing QEMU devel & the CPU model maintainers for opinions.

I think that QEMU should figure out some pattern for naming CPU models
because it's one big mess.  EPYC and Ryzen are bad names for QEMU as
Core/Xeon would be for Intel CPUs.  It's the name of a model families
and it will probably remain the same but with different
microarchitecture.

Better name would be similarly like for the latest Inter CPUs,
Skylake-Client and Skylake-Server.  Currently AMD has already two
microarchitectures, Zen and Zen+ and there is third one Zen 2 planned.

Zen has AMD Ryzen, AMD Ryzen Threadripper and AMD Epyc.
Zen+ has AMD Ryzen, AMD Ryzen Threadripper

And I bet that Zen 2 will follow the same model families.

We probably cannot rename EPYC now, but before we introduce Ryzen and
Threadripper let's thing about it and come up with better names, for
example Zen-Client/Zen-Server Zen+-Client or something like that.

Pavel
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