What is the resolution of windows high performance counter?

Question

This might seem like a really basic question but, When dividing the output of

QueryPerformanceCounter with QueryPerformanceFrequency, what is the resulting value in, i.e. seconds, milliseconds, microseconds?

I'm asking because I'm porting some code from Windows to Linux and I don't have a windows machine handy to experiment with. Some googling around provided no concrete answer for me.

Answer 1

We've updated the documentation for QueryPerformanceCounter, and the comparison between RDTSC and QueryPerformanceCounter accuracy above isn't quite right. For further information please see

http://msdn.microsoft.com/en-us/library/windows/desktop/dn553408(v=vs.85).aspx

Ed Briggs Microsoft Corporation

Answer 2

Some googling around provided no concrete answer for me.

First Google search result for "QueryPerformanceCounter": the MSDN documentation for QueryPerformanceCounter()

Here's what it has to say:

Parameters

lpPerformanceCount [out]

Type: LARGE_INTEGER*

A pointer to a variable that receives the current performance-counter value, in counts.

First Google search result for "QueryPerformanceFrequency": the MSDN documentation for QueryPerformanceFrequency()

Here's what it has to say:

Parameters

lpFrequency [out]

Type: LARGE_INTEGER*

A pointer to a variable that receives the current performance-counter frequency, in counts per second. If the installed hardware does not support a high-resolution performance counter, this parameter can be zero.

The value obtained from QueryPerformanceCounter() is in counts. The value obtained from QueryPerformanceFrequency() is in counts per second. Using a bit of dimensional analysis:

(counts) / (counts/second) = seconds

Therefore, the result of dividing the two values is in seconds.