timeGetTime vs. QueryPerformanceCounter

Glenn9999 · Dec 26, 2007

Something I was curious about as I was trying to get some good program timing code working:

I notice these two values aren't anywhere in sync in terms of what the numbers are. (This is after I take QPC / (QPF / 1000) of course.) I was wondering if anyone knew the difference between the two numbers and where they came from.

Is QPC/QPF somehow hardware dependent compared to timeGetTime being software? Or is there some other explanation?

ArkM · Jan 23, 2008

What's a problem?
1. Yes, QPF returned value is hardware dependent (but it's not a CPU frequency!).
2. timeGetTime has 1 millisecond precision by default (too low

.
3. To obtain short time interval(s) by QPF/QPC calls:

Code:

#include <windows.h>
...
LARGE_INTEGER
  f,  /* HPC ticks per second */
  t0, /* start counter */
  t1; /* end counter value */
double micros; // want in microseconds, see 1e6 constant
...
if (QueryPerformanceFrequency(&f))
{
   printf("Performance Frequency is %d\n",(int)f.QuadPart);
   if (QueryPerformanceCounter(&t0))
   {
      /* ** tested code here ** */
      if (QueryPerformanceCounter(&t1))
      {
         micros = (double)(t1.QuadPart - t0.QuadPart) * 1e6
                  /
                  (double)x.QuadPart;
         printf("Elapse time is %g microseconds\n",micros);
      }
   }
}
else
   printf("*** QPF failed.\n");
...

ArkM · Jan 23, 2008

Sorry, must be (double)f.QuadPart divider...

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timeGetTime vs. QueryPerformanceCounter

Glenn9999

Programmer

ArkM

IS-IT--Management

ArkM

IS-IT--Management

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