Timers

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This page serves as a gateway for information related to computing the elapsed time between two positions in your software. This page serves as a gateway for information related to computing the elapsed time between two positions in your software.
-==C/C++==+==cycle counting (rdtsc cycle counter)==
 +* [http://www.mcs.anl.gov/~kazutomo/rdtsc.html source code]
 +* precise
 +* cpu frequency required
 +** get the cpu frequency in MHz with <code>
 + cat /proc/cpuinfo | grep -i "cpu MHZ" -m 1 | awk '{print $4}'</code>
 +example code <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 );</code>
 +* low cost and high resolution
-1- cycle counting (rdtsc cycle counter) - [http://www.mcs.anl.gov/~kazutomo/rdtsc.html source code]+==MPI_WTime()==
-* precise (CS)+* May offer a high resolution than 1 second.
-* cpu frequency required+** MPI_WTick() - query to determine resolution.
-* low cost and resolution (OS)+
-2- MPI_WTime()+==getTimeOfDay() and friends (sys/time.h)==
-* May offer a high resolution than 1 second.(CS)+* portable
 +* not always precise or accurate
 +* may be relatively expensive on IBM BG (compared to cycle counting)
-3- MPI_WTick()+==time.h/ctime.h functions ==
-* can be queried to determine resolution. (CS)+* [http://www.cppreference.com/wiki/c/date/start Reference]
- +* Have a higher resolution than 1 second
-4- getTimeOfDay() and friends (sys/time.h)+* clock function returns elapsed CPU cycles
-* portable (BM)+* Needs cpu frequency which may be inaccurate on POSIX compilers
-* not always precise or accurate (BM)+
-* may be relatively expensive on IBM BG (compared to cycle counting) (OS)+
- +
-5- time.h/ctime.h functions (Reference : http://www.cppreference.com/wiki/c/date/start )+
-* Have a higher resolution than 1 second (CS)+
-* clock function returns elapsed CPU cycles (CS)+
-* Needs cpu frequency which may be inaccurate on POSIX compilers (CS)+
- +
-Note: Feel free to make corrections -- MM+
[[Category:Tutorials]] [[Category:Tutorials]]
[[Category:Software]] [[Category:Software]]

Current revision

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

Contents

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

MPI_WTime()

  • May offer a high resolution than 1 second.
    • MPI_WTick() - query to determine resolution.

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

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

time.h/ctime.h functions

  • Reference
  • 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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