Timers

From ScorecWiki

(Difference between revisions)
Jump to: navigation, search
Revision as of 15:03, 7 August 2011
Cwsmith (Talk | contribs)

← Previous diff
Current revision
Cwsmith (Talk | contribs)

Line 1: Line 1:
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]
-1- cycle counting (rdtsc cycle counter) - [http://www.mcs.anl.gov/~kazutomo/rdtsc.html source code]+
* precise * precise
* cpu frequency required * cpu frequency required
Line 20: Line 19:
* low cost and high resolution * low cost and high resolution
-2- MPI_WTime()+==MPI_WTime()==
* May offer a high resolution than 1 second. * May offer a high resolution than 1 second.
 +** MPI_WTick() - query to determine resolution.
-3- MPI_WTick()+==getTimeOfDay() and friends (sys/time.h)==
-* can be queried to determine resolution. +
- +
-4- getTimeOfDay() and friends (sys/time.h)+
* portable * portable
* not always precise or accurate * not always precise or accurate
* may be relatively expensive on IBM BG (compared to cycle counting) * 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 )+==time.h/ctime.h functions ==
 +* [http://www.cppreference.com/wiki/c/date/start Reference]
* Have a higher resolution than 1 second * Have a higher resolution than 1 second
* clock function returns elapsed CPU cycles * clock function returns elapsed CPU cycles

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
Personal tools