Timers

From ScorecWiki

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 (CS)
• cpu frequency required
  • get the cpu frequency with

   cat /proc/cpuinfo | grep -i "cpu MHZ" -m 1 | awk '{print $4}'

• • sample code

   #define CPUFREQ <INSERT FREQUENCY IN Hz HERE> 
   total_time = finish_time - start_time;  
   printf ("It took %.8lf seconds.\n", total_time / CPUFREQ );

• low cost and resolution (OS)

2- MPI_WTime()

• May offer a high resolution than 1 second.(CS)

3- MPI_WTick()

• can be queried to determine resolution. (CS)

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

• portable (BM)
• 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