Re: [Xen-devel] [PATCH v13] tolerate jitter in cpu_khz calculation to avoid TSC emulation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.03.19 at 14:51, <olaf@xxxxxxxxx> wrote:
> Am Wed, 13 Mar 2019 03:18:39 -0600
> schrieb "Jan Beulich" <JBeulich@xxxxxxxx>:
> 
>> > +    if ( tmp >= VTSC_MEASUREMENT_INACCURACY_RANGE_KHZ )
>> > +        tmp -= VTSC_MEASUREMENT_INACCURACY_RANGE_KHZ;  
>> The discontinuity is still there, and so far you've failed to explain
>> why a discontinuity is what you want here.
> 
> This exists to make sure the non-emulated case stays within the PPM range.

Staying within range is orthogonal to the introduction of any
discontinuities. I can only draw the same table again:

   tmp (initial)        |   tmp (result)
   0            |   0
   1            |   1
   ...
   198          |   198
   199          |   199
   200          |   0
   201          |   1
   ...
   398          |   198
   399          |   199
   400          |   200
   401          |   201
   ...
   400000               |   399800

Why is there this big step between 199 and 200? And why does an
initial value of 200 get handled the same as an initial value of 0, but
then 400 doesn't get handled this same way again? And (seeing the
last row I've added now) how is the result staying in range?

Jan



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