High-resolution timer for C++

Howdy ho! My name is Simon Wybranski, I am a developer on the C++ AMP team!

In this blog post I am going to present a high-resolution timer for measuring the performance of C++ AMP algorithms. There is nothing specific in it to C++ AMP, so it can be used to measure elapsed time of your PPL algorithms or any other C++ code.

Listing of timer.h:

  1: #pragma once
  2: #include <windows.h>
  3:  
  4: struct Timer
  5: {
  6:     void Start() 
  7:     {
  8:         QueryPerformanceCounter(&m_start);
  9:     }
  10:  
  11:     void Stop() 
  12:     {
  13:         QueryPerformanceCounter(&m_stop);
  14:     }
  15:     
  16:     // Returns elapsed time in milliseconds (ms)
  17:     double Elapsed()
  18:     {
  19:         return (m_stop.QuadPart - m_start.QuadPart - m_overhead) \
  20:                                           * 1000.0 / m_freq.QuadPart;
  21:     }
  22:  
  23: private:
  24:  
  25:     // Returns the overhead of the timer in ticks
  26:     static LONGLONG GetOverhead()
  27:     {
  28:         Timer t;
  29:         t.Start();
  30:         t.Stop();
  31:         return t.m_stop.QuadPart - t.m_start.QuadPart;
  32:     }
  33:  
  34:     LARGE_INTEGER m_start;
  35:     LARGE_INTEGER m_stop;
  36:     static LARGE_INTEGER m_freq;
  37:     static LONGLONG m_overhead;
  38: };

Listing of timer.cpp:

  1: #include "timer.h"
  2:  
  3: // Initialize the resolution of the timer
  4: LARGE_INTEGER Timer::m_freq = \
  5:           (QueryPerformanceFrequency(&Timer::m_freq), Timer::m_freq);
  6:  
  7: // Calculate the overhead of the timer
  8: LONGLONG Timer::m_overhead = Timer::GetOverhead();

Snippet showing the usage:

  1: Timer t; 
  2: t.Start(); 
  3: // Your algorithm goes here 
  4: t.Stop(); 
  5:  
  6: std::cout << t.Elapsed() << " ms" << std::endl; 

Enjoy!!

timer.zip

Comments

• Anonymous
  December 28, 2011
  This seems a very naive example of using the a timer which disrespects Microsoft's own advice about jumps in the timer and multiple CPUs.

• Anonymous
  December 28, 2011
  The comment has been removed

• Anonymous
  January 03, 2012
  Hi Saphira, You are right, it is a simple wrapper class over QPC() API. It met my needs, but certainly might be not good everyone. You can adapt it to account for possible jumps and multiprocessor system with these changes:

1. Call SetThreadAffinityMask in the constructor, constraint thread to run on the same processor.
2. Call GetTickCount() in Start() and Stop() member functions, use these measurements to detect possible jump when Elapsed() is called. Here is a code example for that: msdn.microsoft.com/.../ms724408(v=vs.85).aspx Finally, please check the link that Matthew shared in his comment for more advanced timer that might suit you better.

• Anonymous
  January 21, 2012
  The comment has been removed
• Anonymous
  January 23, 2012
  The comment has been removed
• Anonymous
  September 29, 2012
  How about a simple <pre></pre> for code?  The way you have it, well, try to copy and paste it.