HOWTO: Use QueryPerformanceCounter to Time Code
The information in this article applies to:
Microsoft Excel 2000
Microsoft Visual Basic Learning Edition for Windows 5.0
Microsoft Visual Basic Learning Edition for Windows 6.0
Microsoft Visual Basic Professional Edition for Windows 5.0
Microsoft Visual Basic Professional Edition for Windows 6.0
Microsoft Visual Basic Enterprise Edition for Windows 5.0
Microsoft Visual Basic Enterprise Edition for Windows 6.0
Microsoft Visual Basic Control Creation Edition for Windows 5.0
Microsoft Visual Basic Standard Edition, 32-bit, for Windows 4.0
Microsoft Visual Basic Professional Edition, 32-bit, for Windows 4.0
Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows 4.0
Microsoft Access 2002
Microsoft Access 2000
Microsoft Access 97
Microsoft Access for Windows 95 7.0
Microsoft Excel 2002
Microsoft Excel 97 for Windows
Microsoft Excel for Windows 95 7.0
Microsoft Word 2002
Microsoft Word 2000
Microsoft Word 97 for Windows
This article was previously published under Q172338
SUMMARY
When timing code to identify performance bottlenecks, you want to use the highest resolution timer the system has to offer. This article describes how to use the QueryPerformanceCounter function to time application code.
MORE INFORMATION
Several timers of differing accuracy are offered by the operating system: Function Units Resolution
---------------------------------------------------------------------------
Now, Time, Timer seconds 1 second
GetTickCount milliseconds approx. 10 ms
TimeGetTime milliseconds approx. 10 ms
QueryPerformanceCounter QueryPerformanceFrequency same
If your system supports a high-resolution counter, you can use QueryPerformanceCounter and QueryPerformanceFrequency to do high-resolution timings.
The following sample code compares the various counters:
WARNING: ANY USE BY YOU OF THE CODE PROVIDED IN THIS ARTICLE IS AT YOUR OWN RISK. Microsoft provides this code "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose.
Step-by-Step Procedures
Enter the following code into a Module. If you enter it into a class, form, or report module, make the declarations Private. Option Explicit
Declare Function QueryPerformanceCounter Lib "Kernel32" _
(X As Currency) As Boolean
Declare Function QueryPerformanceFrequency Lib "Kernel32" _
(X As Currency) As Boolean
Declare Function GetTickCount Lib "Kernel32" () As Long
Declare Function timeGetTime Lib "winmm.dll" () As Long
Sub Test_Timers()
Dim Ctr1 As Currency, Ctr2 As Currency, Freq As Currency
Dim Count1 As Long, Count2 As Long, Loops As Long
'
' Time QueryPerformanceCounter
'
If QueryPerformanceCounter(Ctr1) Then
QueryPerformanceCounter Ctr2
Debug.Print "Start Value: "; Format$(Ctr1, "0.0000")
Debug.Print "End Value: "; Format$(Ctr2, "0.0000")
QueryPerformanceFrequency Freq
Debug.Print "QueryPerformanceCounter minimum resolution: 1/" & _
Freq * 10000; " sec"
Debug.Print "API Overhead: "; (Ctr2 - Ctr1) / Freq; "seconds"
Else
Debug.Print "High-resolution counter not supported."
End If
'
' Time GetTickCount
'
Debug.Print
Loops = 0
Count1 = GetTickCount()
Do
Count2 = GetTickCount()
Loops = Loops + 1
Loop Until Count1 <> Count2
Debug.Print "GetTickCount minimum resolution: "; _
(Count2 - Count1); "ms"
Debug.Print "Took"; Loops; "loops"
'
' Time timeGetTime
'
Debug.Print
Loops = 0
Count1 = timeGetTime()
Do
Count2 = timeGetTime()
Loops = Loops + 1
Loop Until Count1 <> Count2
Debug.Print "timeGetTime minimum resolution: "; _
(Count2 - Count1); "ms"
Debug.Print "Took"; Loops; "loops"
End Sub
Run the function from the Debug/Immediate window. Your output should appear similar to the following:
Start Value: 3516284.3498
End Value: 3516284.3521
QueryPerformanceCounter minimum resolution: 1/1193182 sec
API Overhead: 1.92761875388667E-05 seconds
GetTickCount minimum resolution: 10 ms
Took 650 loops
timeGetTime minimum resolution: 10 ms
Took 1565 loops
Multiple statements execute before either GetTickCount or timeGetTime record a change. The actual number of loops will vary depending on the background tasks the operating system is executing.
On the other hand, QueryPerformanceCounter changes value between successive API calls, indicating its usefulness in high-resolution timing. The resolution in this case is on the order of a microsecond. Because the resolution is system-dependent, there are no standard units that it measures. You have to divide the difference by the QueryPerformanceFrequency to determine the number of seconds elapsed. In the case above, the overhead for just calling the API is about 19 microseconds. This would have to be subtracted when timing other code as follows: Private Sub Time_Addition()
Dim Ctr1 As Currency, Ctr2 As Currency, Freq As Currency
Dim Overhead As Currency, A As Long, I As Long
QueryPerformanceFrequency Freq
QueryPerformanceCounter Ctr1
QueryPerformanceCounter Ctr2
Overhead = Ctr2 - Ctr1 ' determine API overhead
QueryPerformanceCounter Ctr1 ' time loop
For I = 1 To 100
A = A + I
Next I
QueryPerformanceCounter Ctr2
Debug.Print "("; Ctr1; "-"; Ctr2; "-"; Overhead; ") /"; Freq
Debug.Print "100 additions took";
Debug.Print (Ctr2 - Ctr1 - Overhead) / Freq; "seconds"
End Sub
Sample output:
( 3630876.6256 - 3630876.6388 - 0.0013 ) / 119.3182
100 additions took 9.97333181358753E-05 seconds
NOTE: Because currency variables are used, the values returned are 10000 times smaller than the actual counters. Because the calculation of seconds involves a division operation, this factor is cancelled out.
REFERENCES
Microsoft Developer Network; topics: timeGetTime GetTickCount QueryPerformanceCounter QueryPerformanceFrequency
Last Reviewed: 5/12/2003
Keywords: kbhowto kbProgramming KB172338
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q172338
