[Beowulf] Intel quad core nodes?

[Mark Hahn]

> I'm moving towards setting up a small cluster (my first), and am thinking 
> about using Intel quad core processors.  However, I'm a little concerned 
> about memory contention.

very sensible.  well, assuming you already know that your workload
is cache-unfriendly - do you?

> I'm (tentatively) going to have one processor per 
> node (this appears to be the cheapest way to go),

1 socket nodes are attractive mainly because you get to use lower-grade
hardware.  oops, that sounds bad - let's call it "higher price/performance".
for instance, non-ECC dimms, for intel, even non-FB.  "desktop" rather than
"server" processors.  motherboards which are in much higher levels of
production. dispensing with 1U chassis (minitowers instead) saves even more.

all these optimizations involve some compromise of the final reliability
and/or features.  which is not to say that they never make good sense!

> but I still wonder whether 
> four cores will choke Intel's memory architecture.

depends on the workload - specifically the application's cache miss rate.
just the obvious: if misses are low, don't worry about ram too much...

> (AMD's Barcelona may be 
> better in this regard, but it doesn't seem to be available yet, at least not 
> through retail channels).

they do seem to be available, but not effusively.  that's probably because 
the currently available stepping seems to be a bit of a compromise to release
early and/or with low power consumption.

in any case, the place where AMD really shines is scaling from 2-4 sockets.
at a single socket, the K10 is good, but matchable by Intel.  note also that 
the K10 isn't released yet in non-server versions

> I'd like to hear any opinions on this issue.  And if you've used quad core 
> processors, I'd certainly like to hear about your experiences (including 
> which processor you've used).

no slight intended, but I don't think this query makes much sense.  there's
not really anything new about quad-cores, since over the years there have
been chips at most any place along the flops-per-bandwidth ("balance"
ala http://www.cs.virginia.edu/stream/analyses.html) continuum.  any answer
would depend on the particular cache working set of the benchmark - for an
attempt at a more general but vague answer, your best bet would probably be
to go straight to http://www.spec.org/cpu2006/results/.  (hard to tell from
your query whether you should pay attention first to int or fp, or even 
serial vs rate results...)

> PS I couldn't find any discussion of Intel's quad core processors in the 
> archive, but if I missed one, please point me to it.

a single intel quad-core chip should behave very similar to a pair of 
dual-core chips.  cache sizes probably won't line up exactly, nor will
minor version changes in SSE, etc, and iirc the earliest Core2 chips had
just 1066 MHz FSB, vs 1333 now.  you can probably come pretty close by
populating just one node's dimms on a dual-socket AMD system.

regards, mark hahn.