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

[Rahul Nabar]

Is it a bad mistake to configure a Nehalem (2 sockets quad core giving
a total of 8 cores; E5520) with 16 GB RAM (4 DIMMs of 4GB each)? I
know (I think) that the optimized memory for Nehalems is in banks of 6
due to the way the architecture is? I have often seen Nehalems coming
with 24 GB memory as 6 DIMMs of 4 GB each.

Our code requirements dictate 2 GB / core is enough. Should I be
paying for the additional RAM to make it 24 GB?

Also, are there any other tips for the Nehalems in general to coax out
max performance? Maybe some compiler flags or BIOS settings etc? The
only thing I did so far was to put the BIOS power setting into a "max
performance" mode.

In the past I've gotten about  5% additional performance by changing
the power profile to "performance" using cpu-freq-set on my AMD
Opteron Barcelonas. Any similar gotchas for the Nehalems and HPC?

-- 
Rahul