[Xen-devel] RE: expose MWAIT to dom0

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Keir Fraser [mailto:keir.xen@xxxxxxxxx]
> Sent: Monday, August 15, 2011 2:55 PM
> 
> On 15/08/2011 06:35, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
> 
> > Above trick is ugly and error-prone, since it always enable mwait regardless
> > of
> > actual CPU capability. It's unlikely to make into upstream, and also get 
> > lost
> > in
> > into some distro such as SLES11.
> >
> > Instead of enhancing current approach (e.g. add a separate channel to reveal
> > mwait capability instead of using cpuid), I'm curious why we don't expose
> > mwait
> > in cpuid to dom0 directly. At least original comment in 17573 looks obscure,
> > since EIST has nothing to do with Cx...
> 
> Well the problem is some older kernels will try to use MWAIT if they see the
> feature in CPUID. Of course that doesn't work outside ring 0.
> 

if those old kernels are still of interest, then possibly a boot option in Xen 
would
be applausive. Or can we just allow selectively exposing MWAIT when xen 
cpuidle is enabled?

Thanks
Kevin

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