Re: [Xen-devel] [PATCH v5] new config option vtsc_tolerance_khz to avoid TSC emulation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.03.18 at 10:32, <olaf@xxxxxxxxx> wrote:
> On Thu, Mar 29, Roger Pau Monné wrote:
> 
>> IMO if hardware TSC scaling is supported vtsc_tolerance_khz should be
>> ignored, and the TSC should be scaled by the hardware always in order
>> to provide accurate values.
> 
> Good point, I will double check that part and do nothing if hardware
> scaling happens to be available on the current host.

... and it's a HVM guest. I was actually under the impression that

         if ( tsc_mode == TSC_MODE_DEFAULT && host_tsc_is_safe() &&
-             (d->arch.tsc_khz == cpu_khz ||
+             (disable_vtsc ||
               (is_hvm_domain(d) &&
                hvm_get_tsc_scaling_ratio(d->arch.tsc_khz))) )
         {

is already taking care of this case.

Jan

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