OpenMP Multi-Core/Multi-Processor Question

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OpenMP Multi-Core/Multi-Processor Question

Postby milan » Tue Jan 29, 2008 7:15 pm

I will soon be building a workstation with 4 processors. Each processor will have 4 cores, totaling 16 cores. I will have 4 distributed shared memory slots - 1 processor (ie. 4 cores) per shared memory slot.

Can OpenMP run on more than 1 processor, or would the operating system choose to run all the threads on 1 processor shared between the 4 cores?

If I want to take full advantage of this architecture, would I have to write an MPI program embedded with OpenMP? For example, would I have to specify to use 4 processors in MPI and 4 threads in OpenMP to achieve full usage of the 16 cores? How else can this be done?

Thank you for your time and help.

-Milan
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Re: OpenMP Multi-Core/Multi-Processor Question

Postby ejd » Wed Jan 30, 2008 6:16 am

OpenMP is for shared memory architectures. I am not quite sure of your configuration. It sounds as if each processor shares memory between cores, but that the processors don't share any memory. If this is the case, then you would have to do as suggest and use MPI and OpenMP. The other alternative (if these are Intel chips), is to use Intel's cluster OpenMP. I believe Intel's implementation would allow you to spread the work across all of the cores.
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Re: OpenMP Multi-Core/Multi-Processor Question

Postby milan » Wed Jan 30, 2008 9:35 am

Thanks for the clarification ejd!

One last thing:

On the architecture I outlined previously, If I run OpenMP with 16 threads, would they be interlaced between the 4 cores on 1 processor (which is chosen by the operating system)?

Thanks again.

-Milan

PS. It is the case where the processors do not share memory; only the 4 cores in each processor share memory between themselves.
milan
 

Re: OpenMP Multi-Core/Multi-Processor Question

Postby ejd » Wed Jan 30, 2008 10:11 am

milan wrote:One last thing:

On the architecture I outlined previously, If I run OpenMP with 16 threads, would they be interlaced between the 4 cores on 1 processor (which is chosen by the operating system)?


That is what an implementation of the OpenMP spec would do. It would most likely be quite a bit slower than if you ran it using 4 threads.
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Re: OpenMP Multi-Core/Multi-Processor Question

Postby milan » Sun Feb 17, 2008 2:23 pm

Thanks again ejd! It's all clear now!

-Milan


Last bumped by Anonymous on Sun Feb 17, 2008 2:23 pm.
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