[Beowulf] Intel Quad-Core or AMD Opteron

[Mark Hahn]

> As you may be aware of, Intel has reduced the price of its Quad CPUs,
> dramatically.

Intel and AMD have been competing well for a while now.  this is a good
thing.  I wouldn't say that either has the upper hand in price or price/perf,
since their products current and upcoming, differ significantly.  Intel's 
core2 microarchitecture has excellent in-cache performance, but AMD still 
has a better memory system.  it's unclear whether AMD's core update will
change this picture enough to make things decisive.  in any case, the nature
of your workload is the only way to judge which direction to go.

> Does anyone have any experience using Intel Quad-Core CPUs in a Beowulf
> Cluster?

an intel quad-core chip is just like a pair of intel dual-core chips 
(assuming both are core2 and equating for cache size and clock.)
not really anything new, except more cores competing for limited memory 
bandwidth (though Intel has made some modest improvements there too.)

> Do you prefer these ones over AMD Opteron?

I really think it boils down to whether your code is cache-friendly.

> Essentially, are Intel Quad CPUs having really FOUR cores? Are they really
> 64-bit processors, as Opterons are?

Intel doesn't yet ship a single-chip quad-core, but that's largely just a 
packaging issue.  Intel core2 chips are certainly 64b processors, though 
it's true that some of the core2 improvements apply only when running in 
32b mode.  I wouldn't be surprised if Intel fixed that in Penryn.

people still overemphasize 64b-ness.  in HPC, x86_64 is important if you have
quite large address spaces, or if you can really take advantage of the better
register sets (more/wider general regs, and sse* ones.)  people seem to
forget that for programs <= 2GB, especially pointer-heavy ones, 32b is
probably faster...

in very broad terms, I'd try to hold off buying current chips because major 
refreshes are coming from both vendors.  but both have very good products - 
much faster and cooler than, say, 2 years ago.