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Groups > comp.lang.c > #130463
| From | "F. Russell" <fr@random.info> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: OpenMP and AVX2 Problem [SOLVED] |
| Date | 2018-05-12 19:42 +0000 |
| Organization | NewsGuy.com |
| Message-ID | <pd7g3301c99@news4.newsguy.com> (permalink) |
| References | <pd703u02761@news2.newsguy.com> |
On Sat, 12 May 2018 15:09:50 +0000, F. Russell wrote: > > Run Time Single-Thread: 0.010427 seconds > Run Time Multi-Thread: 0.05072 seconds > I believe that I have found the reason for the discrepancy. The functions clock(), clock_gettime(CLOCK_PROCESS_CPUTIME_ID), and rusage(RUSAGE_SELF) are indeed the correct functions to measure the CPU time. But for a multi-threaded process these functions will return the SUM of the CPU time used by all threads: https://en.wikipedia.org/wiki/CPU_time Thus, the time returned should be divided by the number of threads to give a rough final value. The number of threads can be specified with the command: OMP_NUM_THREADS=N ./vectprod-parallel The results are consistent: OMP_NUM_THREADS=2 ./vectprod-parallel Run Time Multi-Thread: 10 msec OMP_NUM_THREADS=4 ./vectprod-parallel Run Time Multi-Thread: 20 msec OMP_NUM_THREADS=8 ./vectprod-parallel Run Time Multi-Thread: 42 msec (this value varies a lot from 32 - 52) I believe that this is the correct explanation. If anyone knows better please enlighten us.
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OpenMP and AVX2 Problem "F. Russell" <fr@random.info> - 2018-05-12 15:09 +0000
Re: OpenMP and AVX2 Problem Tim Prince <tprince@intelretiree.com> - 2018-05-12 11:33 -0400
Re: OpenMP and AVX2 Problem Melzzzzz <Melzzzzz@zzzzz.com> - 2018-05-12 16:05 +0000
Re: OpenMP and AVX2 Problem "F. Russell" <fr@random.info> - 2018-05-12 17:46 +0000
Re: OpenMP and AVX2 Problem "F. Russell" <fr@random.info> - 2018-05-12 19:10 +0000
Re: OpenMP and AVX2 Problem [SOLVED] "F. Russell" <fr@random.info> - 2018-05-12 19:42 +0000
Re: OpenMP and AVX2 Problem [SOLVED] Keith Thompson <kst-u@mib.org> - 2018-05-12 14:04 -0700
Re: OpenMP and AVX2 Problem scott@slp53.sl.home (Scott Lurndal) - 2018-05-13 17:47 +0000
Re: OpenMP and AVX2 Problem Wouter Verhelst <w@uter.be> - 2018-05-13 09:57 +0200
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