On Wed, Apr 17, 2019 at 09:26:10PM +0200, Pavel Hrdina wrote: > On Wed, Apr 17, 2019 at 10:53:04PM +0800, Pu Wen wrote: > > On 2019/4/16 22:17, 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? > > > > Right now there's no much difference between Dhyana and EPYC from the > > software's view. Dhyana removed the instructions aes, pclmulqdq, sha_ni > > compared to EPYC, but will have it's own implementation such as for aes in > > future CPU models. Hygon also will implement something different from AMD in > > the future. > > > > > 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? > > > > Also as Eduardo mentioned that there's no CPU model alias or inheritance > > system in x86, so I think it's worthwhile to keep a separate CPU model for > > Hygon. > > So what happens once Zen2 is out and there are new Dhyana CPUs based on > the Zen2 microarchitecture with some new features, what CPU models we > will introduce, EPYC-G2 and Dhyana-G2, but that will not correspond to > the CPU model anymore. > > My idea was that we should probably introduce CPU model Zen-Server which > could cover both EPYC and Dhyana as they are both based on the Zen > microarchitecture. The fact that Dhyana doesn't support all the > features is not an issue as QEMU will not use them if they are not > available on the host.
I don't think this is a good idea. AFAICT, Dhyana and EPYC should not be thought of as the same microarchitecture. Dhyana is a fork of the Zen microarchitecture as illustrated by the dropping of a number of CPU features. The Dhyana SEV patches show that it has had other significant changes, which are likely to require extra work in QEMU to support too. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
