Re: [Qemu-devel] [PATCH v3] i386: Add new Hygon 'Dhyana' CPU model

[Eduardo Habkost]

On Tue, Apr 16, 2019 at 04:17:00PM +0200, Pavel Hrdina wrote:
> On Tue, Apr 16, 2019 at 08:06:13PM +0800, Pu Wen wrote:
> > Add a new base CPU model called 'Dhyana' to model processors from Hygon
> > Dhyana(family 18h), which derived from AMD EPYC(family 17h).
> > 
> > The following features bits have been removed compare to AMD EPYC:
> > aes, pclmulqdq, sha_ni
> > 
> > The Hygon Dhyana support to KVM in Linux is already accepted upstream[1].
> > So add Hygon Dhyana support to Qemu is necessary to create Hygon's own
> > CPU model.
> 
> I have once question that we will have to solve for EPYC CPUs as well.
> The name should not be based on the Product name or Model name as that
> usually doesn't change with introduction of new microarchitecture.
> 
> With EPYC we made a mistake to name the CPU like that, luckily with
> Intel we already use the microarchitecture name, so the EPYC CPU should
> have been named ZEN-Server and for Ryzen CPUs there should be ZEN-Client
> if there is any difference or otherwise we can simply use ZEN.
> 
> The issue here is what happens once the ZEN2 microarchitecture is out
> wihch introduces new features and we will have to come up with a CPU
> name.
> 
> Obviously we cannot change/remove the EPYC models so the question is
> what is the difference between the AMD EPYC CPU and this new Dhyana CPU
> if they are both based on the ZEN microarchitecture?
> 
> In addition is there any way how we can introduce ZEN-Server &
> ZEN-Client or simply ZEN, if there is no difference, as an alias or a
> new model next to the EPYC?

Currently there's no CPU model alias or inheritance system in x86
(yet), but feel free to submit a CPU model that's a copy of EPYC,
including the justification above.

When we implement CPU model versioning, we can make "EPYC" be
translated to "ZEN" by the CPU model version resolution API.

-- 
Eduardo