# Compare programs or subroutine

**URL:** <https://fortran-lang.discourse.group/t/compare-programs-or-subroutine/7882>\
**Category:** Help\
**Created:** [April 20, 2024, 7:18pm UTC](https://fortran-lang.discourse.group/t/compare-programs-or-subroutine/7882 "2024-04-20T19:18:45Z")\
**Posts on this page:** 1\
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**Author:** ![hkvzjal](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/hkvzjal/32/3055_2.png) [@hkvzjal](https://fortran-lang.discourse.group/u/hkvzjal)\
**Post date:** [April 20, 2024, 7:32pm UTC](https://fortran-lang.discourse.group/t/compare-programs-or-subroutine/7882/3 "2024-04-20T19:32:13Z")

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> [@How to show the true wall time instead of cpu\_time?](https://fortran-lang.discourse.group/t/how-to-show-the-true-wall-time-instead-of-cpu-time/2189/7):
>
> A few years ago, I compared time measurement subroutines in Fortran. I recommend date\_and\_time or omp\_get\_wtime (OpenMP’s time measurement function) as time measurement subroutines. For system\_clock, the count rate is different depending on the compiler. Especially for PGI (currently nvfortran), the upper limit of measurement time is about 36 minutes when integer(int32) is used for the count. Also, system\_clock and cpu\_time cannot measure the execution time of a parallelized program. The tabl…

You might find this thread very insightful for a comparison of several methods to measure elapsed time.

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