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> | ||
| Line 18: | Line 18: | ||
| 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
- 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
