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 |
[edit]
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
[edit]
MPI_WTime()
- May offer a high resolution than 1 second.
- MPI_WTick() - query to determine resolution.
[edit]
getTimeOfDay() and friends (sys/time.h)
- portable
- not always precise or accurate
- may be relatively expensive on IBM BG (compared to cycle counting)
[edit]
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
