How to tell if OpenMP is working?

c++ openmp libsvm
paul simmons picture paul simmons · May 7, 2012 · Viewed 8.7k times · Source

I am trying to run LIBSVM in parallel mode, however my question is in OpenMP in general. According to LIBSVM FAQ, I have modified the code with #pragma calls to use OpenMP. I also modified the Makefile (for un*x) by adding a -fopenmp argument so it becomes:

CFLAGS = -Wall -Wconversion -O3 -fPIC -fopenmp

The code compiles well. I check (since it's not my PC) whether OpenMP is installed by :

/sbin/ldconfig -p | grep gomp

and see that it is -probably- installed:

 libgomp.so.1 (libc6,x86-64) => /usr/lib64/libgomp.so.1
 libgomp.so.1 (libc6) => /usr/lib/libgomp.so.1

Now; when I run the program, I don't see any speed improvements. Also when I check with "top" the process is using at most %100 CPU (there are 8 cores), also there is not a CPU bottleneck (only one more user with %100 CPU usage), I was expecting to see more than %100 (or a different indicator) that process is using multiple cores.

Is there a way to check that it is working multiple core?

Answer

Charles Brunet picture Charles Brunet · May 7, 2012

You can use the function omp_get_num_threads(). It will return you the number of threads that are used by your program.

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