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Re: [Qemu-devel] [libvirt] CPU Support

From: Brijesh Singh
Subject: Re: [Qemu-devel] [libvirt] CPU Support
Date: Wed, 18 Jul 2018 21:15:50 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.9.0

On 7/18/18 8:49 AM, Eduardo Habkost wrote:
> CCing the AMD people who worked on this.
> On Wed, Jul 18, 2018 at 12:18:45PM +0200, Pavel Hrdina wrote:
>> 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...

EPYC model should work just fine on Ryzen/Threadripper. Are we seeing
some issues?

>>> 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.

My guess is same as your :) I hope sales/marketing does not come up with
different names for Soc's based Zen 2 core.

>> 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.

Zen-Client/Zen-Server naming convention looks better.

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