Re: [boost] Low-level precision timer proposal

From: Michael Fawcett (michael.fawcett_at_[hidden])
Date: 2006-05-15 15:20:03

On 5/15/06, Silex <silex0r_at_[hidden]> wrote:
> > The problem with QueryPerformanceCounter is that QueryPerformanceFrequency
> > is not (AFAIK) required to return the same value every time. It may be CPU
> > clock based, and a low power CPU can vary its frequency depending on load.
>
> No, "the frequency cannot change while the system is running."

Correct, but that's the problem IIUC.  The CPU's clock speed got cut
by 50% during the thermal throttling, and then increased after the CPU
cooled down, however QPF kept happily returning the same value the
entire time.  Google on SpeedStep and QPF.

There is also a problem with using QPC/QPF on SMP systems, but I am
not knowledgeable about the specifics.

--Michael Fawcett