2 quad cores vs 1 octa core

[sal]

Could buying 2 quad-core and combining them somehow be better than buying 1 octa-core processor, assuming the 2 quad cores are cheaper combined and performance of each individual core is roughly the same? Assume the use for this is running (core-)parallelizable code, i.e. sending large but similarly complex jobs to each core and combining result after the last has finished.

More generally, assuming the more cores the better, is there some "sweet spot" of what kind of processors to combine to make the most cores working together in the cheapest way possible? What are the challenges involved in trying to make many processors work together?

 

[beers]

You'd spend more on the dual socket motherboard. There also aren't very many enthusiast dual socket boards these days, so you'll be more limited than a normal single CPU setup.

Generally I would imagine you would have higher inter-core performance on the same package without having to use QPI out to a separate physical CPU, but additional resources like extra memory channels in multiprocessor server platforms may offset that minor performance loss.