Re: [Xen-devel] [PATCH 00/13] Add VMX TSC scaling support

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 09/28/2015 06:51 AM, Andrew Cooper wrote:
> On 28/09/15 08:13, Haozhong Zhang wrote:
> > This patchset adds support for VMX TSC scaling feature which is
> > available on Intel Skylake CPU. The specification of VMX TSC scaling
> > can be found at
> > http://www.intel.com/content/www/us/en/processors/timestamp-counter-scaling-virtualization-white-paper.html
> >
> > VMX TSC scaling allows guest TSC which is read by guest rdtsc(p)
> > instructions increases in a rate that is customized by the hypervisor
> > and can be different than the host TSC rate. Basically, VMX TSC
> > scaling adds a 64-bit field called TSC multiplier in VMCS so that, if
> > VMX TSC scaling is enabled, TSC read by guest rdtsc(p) instructions
> > will be calculated by the following formula:
> >
> >    guest EDX:EAX = (Host TSC * TSC multiplier) >> 48 + VMX TSC Offset
> >
> > where, Host TSC = Host MSR_IA32_TSC + Host MSR_IA32_TSC_ADJUST.
> >
> > This patchset is composed of following four parts.
> >    1. PATCH 01 - 02 fix bugs in tsc_get_info() which could result in
> >       errors when VMX TSC scaling is used.
> >       
> >    2. PATCH 03 - 09 add/move the common parts of VMX TSC scaling and
> >       SVM TSC ratio to hvm.c and x86/time.c.
> >       
> >    3. PATCH 10 - 12 implement the VMX-specific code for supporting VMX
> >       TSC scaling.
> >       
> >    4. PATCH 13 adapts libxl for VMX TSC scaling (as well as SVM TSC
> >       ratio).
> Thankyou for this series.  I have had a brief look over it and it
> appears to be in good shape, but have not done a thorough review yet.
>
> Konrad/Boris: As Oracle are the main users of the more interesting guest
> timing modes, do you have tests to verify correct functioning?
Not really. The most interesting thing to test here I think would be 
migration between differently-clocked systems and we only do save/restore.
-boris

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