[Beowulf] performance tweaks and optimum memory configs for a Nehalem

[Bill Broadley]

Joshua Baker-LePain wrote:

> Well, as there are only 8 "real" cores, running a computationally
> intensive process across 16 should *definitely* do worse than across 8.

I've seen many cases where that isn't true.  The P4 rarely justified turning
on HT because throughput would often be lower.  With the nehalem often it
helps, the best way to tell is to try it.

> However, it's not so surprising that you're seeing peak performance with
> 2-4 threads.  Nehalem can actually overclock itself when only some of
> the cores are busy -- it's called Turbo Mode.  That *could* be what
> you're seeing.

Indeed.