How to get the current Windows system-wide timer resolution [closed]

Answer 1

The RDTSC instruction may be used to read the CPU time-stamp counter. In most cases (if not all), this counter will change at the CPU clock rate. If you want to be picky, you can also use an instruction like CPUID to serialize instructions. Refer to the Intel manuals for more details.

You can work RDTSC against API's like QueryPerformanceCounter, et al. In other words, use RDTSC before and after a call to make measurements.

Answer 2

This won't be helpful, another process can change it while you are calibrating.

This falls in the "if you can't beat them, join them" category. Call timeBeginPeriod(1) before you start calibrating. This ensures that you have a known rate that nobody can change. Getting the improved timer accuracy surely doesn't hurt either.

Do note that it is pretty unlikely that you can do better than QueryPerformanceFrequency(). Unless you calibrate for a very long time, the clock rate just isn't high enough to give you extra accuracy since you can never measure better than +/- 0.5 msec. And the timer event isn't delivered with millisecond accuracy, it can be arbitrarily delayed. If you calibrate over long periods then GetTickCount64() is plenty good enough.

Answer 3

WINAPI function GetSystemTimeAdjustment

Answer 4

Windows timer resolution is provided by the hidden API call:

NTSTATUS NtQueryTimerResolution(OUT PULONG MinimumResolution, 
                                OUT PULONG MaximumResolution, 
                                OUT PULONG ActualResolution);

NtQueryTimerResolution is exported by the native Windows NT library NTDLL.DLL.

Common hardware platforms report 156,250 or 100,144 for ActualResolution; older platforms may report even larger numbers; newer systems, particulary when HPET (High Precision Event Timer) or constant/invariant TSC are supported, may return 156,001 for ActualResolution.

Calls to timeBeginPeriod(n) are reflected in ActualResolution.

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