Re: [Qemu-devel] [PATCH] i386: add KNM cpu model

[Daniel P . Berrangé]

On Fri, Mar 16, 2018 at 10:11:57AM +0800, Boqun Feng wrote:
> On Wed, Mar 14, 2018 at 01:01:30PM +0000, Daniel P. Berrangé wrote:
> > On Wed, Mar 14, 2018 at 03:29:59PM +0800, Boqun Feng wrote:
> > > A new cpu model called "KNM" is added to model Knights Mill processors.
> > 
> > Why the obscure acryonym? Can't we just call it KnightsMill so it is
> > obvious what it is to everyone, as we've done for all other Intel
> > CPU model names in the past.
> > 
> 
> Ah.. my bad, good point! I will rename to "KnightsMill" in the next
> version.
> 
> > > Compared to "Skylake-Server" cpu model, the following features are
> > > added:
> > > 
> > >   avx512_4vnniw avx512_4fmaps avx512pf avx512er avx512_vpopcntdq
> > > 
> > > and the following features are removed:
> > > 
> > >   pcid invpcid clflushopt avx512dq avx512bw axv512cd clwb smap rtm
> > >   mpx xsavec xgetbv1 hle
> > 
> > "pcid" was one of the features critical to mitigate performance
> > downside of the Meltdown bug fix in guests. Will Knights Mill have
> > a fix for Meltdown in hardware, to avoid the need for split table
> > pages and thus avoid the perf hit in guests ?
> > 
> 
> I got the confirmation the Knights Mill doesn't have PCID at all. For
> the alternative fix for Meltdown in hardware, I will ask around and info
> you if I get something.

No need to wait for an answer to that question - if 'pcid' is not
in hardware, we simply have to accept whatever the answer is. So
just repost with the changed name.

Regards,
Daniel
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