Re: [PATCH 1/5] Add a global synchronization point for pvclock

Avi Kivity
2010-04-19T11:35:50Z

On 04/19/2010 01:59 PM, Peter Zijlstra wrote:
>
>> So what do we need? test for both TSC_RELIABLE and NONSTOP_TSC? IMO
>> TSC_RELIABLE should imply NONSTOP_TSC.
>>
> Yeah, I think RELIABLE does imply NONSTOP and CONSTANT, but NONSTOP&&
> CONSTANT does not make RELIABLE.
>

The manual says:

> 16.11.1 Invariant TSC
>
> The time stamp counter in newer processors may support an enhancement,
> referred
> to as invariant TSC. Processor’s support for invariant TSC is indicated by
> CPUID.80000007H:EDX[8].
> The invariant TSC will run at a constant rate in all ACPI P-, C-. and
> T-states. This is
> the architectural behavior moving forward. On processors with
> invariant TSC
> support, the OS may use the TSC for wall clock timer services (instead
> of ACPI or
> HPET timers). TSC reads are much more efficient and do not incur the
> overhead
> associated with a ring transition or access to a platform resource.

and this maps to NONSTOP, so I think we're fine.

--
error compiling committee.c: too many arguments to function