Q172338: HOWTO: Use QueryPerformanceCounter to Time Code
Article: Q172338
Product(s): Microsoft Visual Basic for Windows
Version(s): 2000,4.0,5.0,6.0,7.0
Operating System(s):
Keyword(s): kbProgramming kbVBp400 kbVBp500 kbhowto
Last Modified: 04-SEP-2001
-------------------------------------------------------------------------------
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. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.
Copyright Microsoft Corporation 1986-2002.