Re: [PATCH] i386: pass CLZERO to guests with EPYC CPU model on AMD ZEN platform

[Eduardo Habkost]

On Thu, Feb 06, 2020 at 09:30:11AM -0600, Babu Moger wrote:
> 
> 
> On 2/5/20 11:53 PM, Ani Sinha wrote:
> > 
> > 
> >> On Feb 6, 2020, at 11:16 AM, Ani Sinha <address@hidden> wrote:
> >>
> >>
> >>
> >>> On Feb 6, 2020, at 5:30 AM, Moger, Babu <address@hidden> wrote:
> >>>
> >>> Ani, I am already working on it.
> >>
> >> Wow, I see a whole new AMD-Rome CPU model with it’s own cache info data : 
> >>
> >> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fqemu-devel%2F157314966312.23828.17684821666338093910.stgit%40naples-babu.amd.com%2F&amp;data=02%7C01%7CBabu.Moger%40amd.com%7Cc566dc5cf3cc407b5ee608d7aac8d9bc%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637165651955089264&amp;sdata=tlafWD6m5%2BZ12cqd4vqJcWh0%2FIgly%2FPVMgAbjxK5Mog%3D&amp;reserved=0
> > 
> > Do you think the ROME specific guest cpu cache data will have significant 
> > impact on performance?
> 
> I have not done performance benchmarks myself. Yes. Rome is expected to
> perform better than its previous generations.

Note that virtual cache information on CPUID doesn't affect host
software or hardware behavior in any way.  In the exceptional
cases it affects performance, it's solely because guest software
behavior changed depending on the cache information it sees.

-- 
Eduardo