[Beowulf] Intel Quad-Core or AMD Opteron

[Douglas Eadline]

Multi-core, I lie awake at night thinking about this stuff.
There seem to be no quick answers.

The thing that amazes me about multi-core is how many people
consider the performance of a single process to be a good measure
of total processor performance. If you are going to by a quad-core
CPU to run one process at a time, then this is good test
otherwise it is like predicting performance of your code
on cluster by running it on the head node as single
serial job.

Over the past 8-10 months I have had the chance to test
Intel quad-core, AMD dual core (soon I'll have some Barcelona's)
and here are my conclusions. The details of what I found are
in my columns in Linux Magazine, which is slowly making its way
to the LM web site (and eventually ClusterMonkey):

 - how well multiple processes run (use memory) on quad-core
   is very application specific. I have a simple test script
   that calculates what I call "effective cores". I have seen
   these results range from about 2-7 on a dual socket quad-core
   Intel system (8 cores total) and a quad socket dual core AMD
   system (8 cores total).

 - running a single copy of the NAS FT benchmark on a clovertown
   was much faster than a comparable Opteron. But, running a parallel
   MPI version of FT on 8 cores showed the AMD system to be faster.

 - on Intel quad-cores where the process is placed can have
   large effect on performance. This is largely due to the
   fact that you have four dual core woodcrests each with it's
   own cache. Naturally, if you have four processes running
   it is best if each one gets its own woodcrest. To the OS
   the all look the same. Other than Intel MPI, I don't
   know of any other MPI that attempts to optimize this.
   Open MPI has some processor affinity but it is
   not all that sophisticated (yet).

 - again depending on the application, GigE may not
   sufficient to support the amount of traffic that
   multi-core can generate. So if your code ran
   well on GigE, it may not on a multi-core cluster.
   Things like IB or Myrinet 10GigE may be needed.

Please note, I am not trying to pick a winner, were that
even possible. I want to state that more than ever testing
your code(s) in parallel on these systems is critical if
you want to get optimal performance.

One other thing I found as well. I recently ran the NAS
parallel benchmarks on a dual socket quad core Intel system
(8 cores total) using both the OpenMP (GNU 4.2) and MPI (LAM)
libraries. Anyone want to guess what produced the best results?

 --
 Doug


> Hi everybody,
>
> As you may be aware of, Intel has reduced the price of its Quad CPUs,
> dramatically.
>
> Does anyone have any experience using Intel Quad-Core CPUs in a Beowulf
> Cluster?
>
> Do you prefer these ones over AMD Opteron?
>
> Essentially, are Intel Quad CPUs having really FOUR cores? Are they really
> 64-bit processors, as Opterons are?
>
> Thanks for any comment on each of my questions.
>
> Wishes,
> rmb
>
>
> --
> Best,
> Ruhollah Moussavi Baygi
>
>
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--
Doug