Re: [Xen-devel] [PATCH v5 1/6] x86/hvm: Collect information of TSC scaling ratio

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

Sorry, forgot sending the last reply to Boris.

On 02/24/16 14:00, Haozhong Zhang wrote:
> On 02/23/16 08:37, Jan Beulich wrote:
> > >>> On 23.02.16 at 15:16, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > On 02/23/2016 09:10 AM, Jan Beulich wrote:
> > >>>>> On 23.02.16 at 15:00, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > >>> On 02/22/2016 09:04 PM, Haozhong Zhang wrote:
> > >>>
> > >>>>    
> > >>>> +    if ( cpu_has_tsc_ratio )
> > >>>> +        svm_function_table.tsc_scaling.ratio_frac_bits = 32;
> > >>>> +
> > >>>
> > >>>>    
> > >>>> +#define hvm_tsc_scaling_supported \
> > >>>> +    (!!hvm_funcs.tsc_scaling.ratio_frac_bits)
> > >>>> +
> > >>> What is the difference (in usage) between cpu_has_tsc_ratio and
> > >>> hvm_tsc_scaling_supported? Isn't the first imply the second (and if yes
> > >>> then what's the reason for having the latter)?
> > >> Iiuc cpu_has_tsc_ratio is AMD/SVM specific, while
> > >> hvm_tsc_scaling_supported is meant to be vendor independent.
> > >
> 
> Yes, it's to be vendor independent. Earlier versions of this patch
> series set a field tsc_scaling_supported in hvm_function_table if
> cpu_has_vmx_tsc_scaling or cpu_has_tsc_ratio. Jan suggested we could get
> the same information if some of other fields are initialized
> conditionally, and no extra field (tsc_scaling_supported) would be
> needed any more.
> 
> > > Ah, OK. Can we then
> > > 
> > > #define hvm_tsc_scaling_supported (cpu_has_vmx_tsc_scaling || 
> > > cpu_has_tsc_ratio)
> > 
> > Why would we? The above is doing precisely (but implicitly) that,
> > just with only one memory access instead of two.
> >
> 
> Boris, does the current one look fine for you, as it does the same thing
> as your suggested one?
> 
> Thanks,
> Haozhong
> 
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