Re: [Xen-devel] [PATCH 2 of 2] vpmu: Add a vpmu cpuid function

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>]

Hi Ian,

Am Freitag 20 Januar 2012, 10:54:44 schrieb Keir Fraser:
> On 20/01/2012 10:49, "Dietmar Hahn" <dietmar.hahn@xxxxxxxxxxxxxx> wrote:
> 
> >> Our CPUID configuration is done per-domain, and from
> >> tools/libxc/xc_cpuid_x86.c. CPUID adjustments implemented within the
> >> hypervisor are generally not acceptable without very good reason.
> > 
> > Then a way is needed to have access to the opt_vpmu_enabled variable within
> > the
> > hypervisor from the tools to decide the enabling of the flag (is there such 
> > a
> > way?) or the mechanism with the boot variable must be changed.
> > The opt_vpmu_enabled boot variable was introduced because of a PMU problem 
> > in
> > the Nehalem cpus leading sometimes to hypervisor crashes. But with the done
> > quirk we never had a crash anymore.
> > So maybe we can always switch on the vpmu stuff in the hypervisor and add a
> > flag in the domain configuration when somebody wants to do some performance
> > tests?
> 
> Yes!
> 
> It's obviously an option of fairly narrow interest. If someone tries to
> enable the per-domain option on a CPU which has problems, you can fail the
> domain creation, or print a warning in the hypervisor log, or whatever. Any
> sensible option in that respect is fine by me!

What is the best solution for this?
A domain specific configuration option is needed (vpmu?) which is usable in
libxc/xc_cpuid_x86.c to select/deselect special vpmu bits in the cpuid command.
Can you point me to an proper example?
Thanks.

Dietmar.

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