2 vs 4-CPU for fixed number of cores

[Ralf Kotulla]

Hello everybody,

I'm planning to build a new server for highly parallel data processing and image manipulation workloads using the latest Intel Xeon CPUs. However, what I'm wondering is: Is there any performance advantage or disadvantage of using 4 vs 2 CPUs, as long as the total number of cores is the same. In other words, would a dual 16-core CPU (32 cores total, e.g. using Xeon E7-4850v4) be any different than a quad 8-core (also 32 cores, e.g. Xeon E7 4809v4).

Price is obviously an issue, and power consumption is different, but all else being equal are there any notable differences with respect to a) computing performance or b) memory bandwidth?

Any insight would be greatly appreciated.

Thanks
Ralf

 

[TheELF]

Communication between CPUs will obviously be slower then between cores on the same CPU,but if and how much difference you might see there depends a lot on the software.

(Also I would change the title to : 2 vs 4 CPUs since your wording is misleading)

 

[StefanR5R]

If your workload is very much constrained by memory bandwidth, then the downsides of more sockets may be outweighed by the availability of double the memory channels.

On the other hand, well parallelized applications are by nature optimized to least inter-processor communication possible. And therefore another question arises: Could two 2P machines connected via Infiniband or RDMA capable Ethernet offer better performance per dollar than a single 4P machine? (Edit: Maybe the application can be distributed over two nodes even without RDMA.)

I'm afraid it will be borderline impossible for you to find straight answers short of actual tests of your particular application with your particular datasets, on actual hardware.