Measuring Performance

From: Kechi Cheng

Date: 7/6/2010

 

Hi,

I am reader of Game Engine Architecture. But I feel confused in chapter 7.5.4.3 that talk about 32-Bit Floating-Point Clocks.

You say the time deltas in floating point format, measured in unit of second. But I don’t understand why you multiply the duration of

CPU Cycles by CPU’s clock frequency. I just think the duration of CPU Cycles should be divided by CPU’s clock frequency. I try to use

WIN32 API to test the result, and the test code like:

// Just test

LARGE_INTEGER dwTest;

QueryPerformanceFrequency(&dwTest);

LARGE_INTEGER dwTest1;

QueryPerformanceCounter(&dwTest1);

Sleep(1000);

LARGE_INTEGER dwTest2;

QueryPerformanceCounter(&dwTest2);

float fHiTimer = (float) (dwTest2.QuadPart - dwTest1.QuadPart) / (float) dwTest.QuadPart;

// Just test

The result is correct, so could you tell me why you multiply by CPU’s clock frequency?

Thanks

Kechi Cheng.

______________________________________________

You are correct, that's a typographical error.  A duration measured in cycles divided by frequency in cycles/second (or multiplied by the inverse frequency, in seconds/cycle) will equal seconds.

Cheers,
J