Timers

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1- cycle counting (rdtsc cycle counter) - [http://www.mcs.anl.gov/~kazutomo/rdtsc.html source code] 1- cycle counting (rdtsc cycle counter) - [http://www.mcs.anl.gov/~kazutomo/rdtsc.html source code]
-* precise (CS)+* precise
* cpu frequency required * cpu frequency required
** get the cpu frequency in MHz with <code> ** get the cpu frequency in MHz with <code>
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total_time = finish_time - start_time; total_time = finish_time - start_time;
printf ("It took %.8lf seconds.\n", total_time / CPUFREQ );</code> printf ("It took %.8lf seconds.\n", total_time / CPUFREQ );</code>
-* low cost and resolution (OS)+* low cost and high resolution
2- MPI_WTime() 2- MPI_WTime()
-* May offer a high resolution than 1 second.(CS)+* May offer a high resolution than 1 second.
3- MPI_WTick() 3- MPI_WTick()
-* can be queried to determine resolution. (CS)+* can be queried to determine resolution.
4- getTimeOfDay() and friends (sys/time.h) 4- getTimeOfDay() and friends (sys/time.h)
-* portable (BM)+* portable
-* not always precise or accurate (BM)+* not always precise or accurate
-* may be relatively expensive on IBM BG (compared to cycle counting) (OS)+* may be relatively expensive on IBM BG (compared to cycle counting)
5- time.h/ctime.h functions (Reference : http://www.cppreference.com/wiki/c/date/start ) 5- time.h/ctime.h functions (Reference : http://www.cppreference.com/wiki/c/date/start )
-* Have a higher resolution than 1 second (CS)+* Have a higher resolution than 1 second
-* clock function returns elapsed CPU cycles (CS)+* clock function returns elapsed CPU cycles
-* Needs cpu frequency which may be inaccurate on POSIX compilers (CS)+* Needs cpu frequency which may be inaccurate on POSIX compilers
- +
-Note: Feel free to make corrections -- MM+
[[Category:Tutorials]] [[Category:Tutorials]]
[[Category:Software]] [[Category:Software]]

Revision as of 15:03, 7 August 2011

This page serves as a gateway for information related to computing the elapsed time between two positions in your software.

C/C++

1- cycle counting (rdtsc cycle counter) - source code

  • precise
  • cpu frequency required
    • get the cpu frequency in MHz with
   cat /proc/cpuinfo | grep -i "cpu MHZ" -m 1 | awk '{print $4}'

example code

   #define CPUFREQ <INSERT FREQUENCY IN Hz HERE> 
   unsigned long long start_time = 0;
   unsigned long long finish_time = 0;
   unsigned long long total_time = 0;
   start_time = rdtsc();
   //do stuff
   finish_time = rdtsc();
   total_time = finish_time - start_time;  
   printf ("It took %.8lf seconds.\n", total_time / CPUFREQ );
  • low cost and high resolution

2- MPI_WTime()

  • May offer a high resolution than 1 second.

3- MPI_WTick()

  • can be queried to determine resolution.

4- getTimeOfDay() and friends (sys/time.h)

  • portable
  • not always precise or accurate
  • may be relatively expensive on IBM BG (compared to cycle counting)

5- time.h/ctime.h functions (Reference : http://www.cppreference.com/wiki/c/date/start )

  • Have a higher resolution than 1 second
  • clock function returns elapsed CPU cycles
  • Needs cpu frequency which may be inaccurate on POSIX compilers
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