Re: Use CPUID to communicate with the hypervisor.

[Avi Kivity <avi@redhat.com>]

Zachary Amsden wrote:
>> Well, that should be clearly defined, that is my point.  When asking the
>> hypervisor for the tsc instead of running a calibration loop, then we
>> have a small bit of paravirtualization:  The guest is aware that it runs
>> on a hypervisor and just asks it directly.  So while we are at it we can
>> also define a way to communicate tsc freq changes between host and
>> guest, so the cost of trap'n'emulate tsc reads can be avoided.  Or we
>> define "tsc is constant" and leave it to the hypervisor to make sure it
>>     
>
> For our purposes, we define TSC is constant.
>   

I believe VMware doesn't actually change cpu frequency dynamically.  But 
what about hypervisors that do?  and what about large machines, which do 
not actually have a constant tsc?

You are defining something as constant which in fact is not constant.

-- 
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