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Fugacity February 8, 2012 12:34

SMP or NUMA scheme for Desktop
My work was nice enough to purchase a new Dell t7500 workstation for CFD [and CAD work] because my laptop is not up to the task. It's a Dell T7500 w/ dual xeon X5647s and 54 GB of RAM right now. Personally I tried to setup an AWS Image but Remote Desktop is against our corp computer policy and is blocked by the firewall(s).

My question is, the BIOS lets me specify a SMP or NUMA RAM scheme. It's running SMP right now and seems fine; would/could NUMA have any tangible performance gains?

[and Yes, I did Google this topic. However, I found no satisfactory answers]

rmh26 February 9, 2012 14:58

It really depends on what software you are using.

For instance, lets say you have some large amount of data you are working on and you have parralized the code using openmp. Under a SMP system the data will be laid out in order in the memory in one large chunk. That memory might be controlled by the memory controller of processor A, ie its local to A. In order for processor B to access it, it will have to send a message to A asking for the data which will be sent back through the QPI (or HT for AMD). These interconnects are very fast at this point so I don't think the performance loss will be so great but it will depend on how compute intensive the operations are. In a NUMA system the data will be laid out in a scattered form so that part of the data is local to A and part of the grid is local to B. I think the memory is assigned on a First Use basis. So you might have to initially declare the data in a parallel manner. So maybe a little bit more work but less data sent between the processors.

If your using a commerical package my gut feeling is that SMP is fine but you could always run some benchmarks and post them up here to let people know.

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