[Omp] Detecting No. of processors during OpenMP execution

[Marina Kraeva]

Hello,

First of all, you can't set the number of processors from within your 
program. The omp_set_num_threads function specifies the number of 
threads, not processors.

To find out the number of threads that are running specific piece of the 
code you can call omp_get_num_threads.

As I understood you would like to know on what processors your threads 
are running. You can try to use something like this:

   #include <unistd.h>
   ...
   char name[50];
   size_t len;
   ...
   gethostname(name, len);
   printf("thread %d is running on hostname %s\n",MyId,name);

Marina.

Waibhav Tembe wrote:

> Hello,
> 
> I am using OpenMP for my application on Linux system using Intel's ecc 
> compiler with -openmp option on a node that has multiple processors 
> sharing memory. Although there is a facility in OpenMP to set the number 
> of processors (by selecting omp_ set_num_threads ), I was  wondering if 
> there is any way (perhaps from the OS)  to check the actual number of 
> processors that were used. For example, if I set num. of threads = 8 and 
> for some reason, only 4 processors are used (each processors typically 
> executes 2 threads), then I would like to be able to generate a report 
> that captures this information. Its going to be used to test the 
> effectiveness of some tools in using the parallel processing 
> capabilities. Is there any way to find IDs of the processors that were 
> used for a specific run of a program?
> I thought of issuing a "ps" command during execution. But I am hoping 
> that there is some smarter way. Any pointers in this direction are welcome!
>  
> Thanks a lot.
> 
> w
> 
> 
> 
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