Re: [Xen-devel] [PATCH v2 00/14] Add VMX TSC scaling support

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

On 12/07/15 17:04, Andrew Cooper wrote:
> On 07/12/15 10:16, Haozhong Zhang wrote:
> > On 12/07/15 10:03, Egger, Christoph wrote:
> >> Did you consider nested virtualization?
> >> L1 hypervisor may have a different tsc scaling
> >> and L2 guest again may have a different tsc scale ratio.
> >>
> > Oh, I forgot this. I'll check the nested TSC scaling code (mostly
> > about nested SVM TSC ratio, because this patch series does not expose
> > VMX TSC scaling to L1 guest).
> >
> > BTW, are there any practical usage scenarios of nested TSC scaling? If
> > any, I may also need to consider adding nested virtualization support
> > to VMX TSC scaling.
> 
> I would say that there are genuine uses for nested TSC scaling.  An L1
> hypervisor is going to want to scale for the same reasons as the L0
> hypervisor.
>
nice to know this.

> Having said that, if TSC scaling is correctly hidden from the L1 guests,
> I would advise against conflating the two issues together.  i.e. getting
> nested TSC scaling working is not a prerequisite for accepting this series.
>

agree, I prefer to posting other standalone patches to support nested
VMX TSC scaling.

Thanks,
Haozhong

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