Re: [Qemu-devel] [PATCH x86-next v2] target-i386: add PCID flag to Westmere, Sandy Bridge and Ivy Bridge

[Eduardo Habkost]

On Sat, Jan 13, 2018 at 08:22:31AM +0100, Vincent Bernat wrote:
>  ❦ 12 janvier 2018 16:47 -0200, Eduardo Habkost <address@hidden> :
> 
> > Adding Westmere-PCID would require adding a Westmere-PCID-IBRS
> > CPU model too, so this is starting to look a bit ridiculous.
> > Sane VM management systems would know how to use
> > "-cpu Westmere,+pcid" without requiring new CPU model entries in
> > QEMU.  What's missing in existing management stacks to allow that
> > to happen?
> 
> That's what I actually do. So, I am fine with the solution of doing
> nothing. However, it would be nice for unaware people to get the speedup
> of pcid without knowing about it. Maybe we can just forget about
> Westmere and still apply it to Sandy Bridge and Ivy Bridge.

If management stacks today don't let the user choose
"Westmere,+pcid", we probably have no other choice than adding a
Westmere-PCID CPU model.  But our management stacks need to be
fixed so we won't need similar hacks in the future.

-- 
Eduardo