DOCUMENT:Q172338 04-SEP-2001 [vbwin] TITLE :HOWTO: Use QueryPerformanceCounter to Time Code PRODUCT :Microsoft Visual Basic for Windows PROD/VER::2000,4.0,5.0,6.0,7.0 OPER/SYS: KEYWORDS:kbProgramming kbVBp400 kbVBp500 kbhowto ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Control Creation Edition for Windows, version 5.0 - Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 - Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 - Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 - Microsoft Access 2002 - Microsoft Access 2000 - Microsoft Access 97 - Microsoft Access for Windows 95, version 7.0 - Microsoft Excel 2002 - Microsoft Excel 2000 - Microsoft Excel 97 for Windows - Microsoft Excel for Windows 95, version 7.0 - Microsoft Word 2002 - Microsoft Word 2000 - Microsoft Word 97 for Windows ------------------------------------------------------------------------------- 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 ----------------------- 1. 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 2. 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 Additional query words: ====================================================================== Keywords : kbProgramming kbVBp400 kbVBp500 kbhowto Technology : kbWordSearch kbVBSearch kbExcelSearch kbAudDeveloper kbAccessSearch kbWord2000Search kbWord2000 kbWord2002 kbWord2002Search kbWord97 kbWord97Search kbZNotKeyword6 kbAccess2000 kbAccess2002 kbAccess97 kbExcel2002 kbExcel2000 kbExcel95 kbZNotKeyword2 kbVB500Search kbVB600Search kbAccess2000Search kbAccess2002Search kbVBA500Search kbVB500 kbVB600 kbExcel2000Search kbAccess97Search kbAccess95Search kbExcel95Search kbExcel97Search kbVB400Search kbExcel2002Search kbVB400 kbZNotKeyword3 kbAccess700 kbExcelWinSearch Version : :2000,4.0,5.0,6.0,7.0 Issue type : kbhowto ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. 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