Unix Timing API
Unix standard C libraries provide a number of standard function calls for getting timing data from your program. A simple form of instrumentation may be achieved by logging milestones and time measurements during the execution of a program. While logging does impact runtime performance, it can be targeted to specific locations in the code rather than applied globally.
The following table describes the library calls available for various Unix systems.
| Routine | Include File | Type | Resolution (usec) | OS/Compiler |
|---|---|---|---|---|
| times | sys/times.h | user, sys | 1000 | Linux, AIX, IRIX, UNICOS |
| getrusage | sys/resource.h | wall, user, sys | 1000 | Linux, AIX, IRIX |
| gettimeofday | sys/time.h | wall | 1 | Linux, AIX, IRIX, UNICOS |
| __rdtsc | x86intrin.h | wall | 0.1 | Linux |
| read_real_time | sys/time.h | wall | 0.001 | AIX |
| system_clock | (n/a) | wall | (system dependent) | Fortran 90 intrinsic |
| MPI_Wtime | mpi.h | wall | MPI_Wtick | MPI Library (C, Fortran) |
| omp_get_wtime | omp.h | wall | omp_get_wtick | OpenMP Library (C, Fortran) |
Generally, these functions return some form of a timestamp, so you'll need to calculate differential times in order to measure execution time. The exception is getrusage, which records the time utilization by the calling process. Differential measurements usually take the following form: