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

[Keir Fraser <keir@xen.org>]

On 20/01/2012 10:49, "Dietmar Hahn" <dietmar.hahn@ts.fujitsu.com> 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!

 -- Keir