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Of Pentium D, Ethernet, and those assumption we all make

Recently, I did some benchmarking using Intel Pentium D® processors and gigabit Ethernet. The data are pretty impressive. If I were a non-technical person, I would probably say, Pentium D kicks ass, but you know, I like numbers and have a professional reputation to uphold. Therefore, in a professional sense I can say, Pentium D really kicks ass. To prove my point, this article presents some of the highlights from a recent white paper I prepared for Appro International called Achieving High Performance at Low Cost: The Dual Core Commodity Cluster Advantage. For a more complete description of the tests and results (including benchmark numbers) you probably want to download the white paper.

Back In The Day

Back when clusters started stirring up trouble in High Performance Computing (HPC) world, there were those that said things like, there is no way commodity hardware can stand up against real iron, or you cannot build a real supercomputer from PC parts. We all know how that turned out.

Today's cluster nodes typically have dual cores sitting in dual sockets connected by a low latency/high throughput network. In market terms, this is data center/sever level hardware -- the good stuff (and expensive). At the lower end of the spectrum is the desk-top hardware, which one would assume is not really up to snuff as far as HPC goes. You certainly cannot build a real supercomputer from this type of hardware, you probably have to use gigabit Ethernet for heavens sake! Sounds like an assumption to me. Some numbers are needed.

In the past, fellow monkey Jeff Layton and I have written about very low cost commodity computing where $2500 can get you 14.5 GFLOPS running HPL (the Top500 Benchmark). These results can easily be improved upon today as the tests were performed in 2004. Indeed, the introduction of low cost dual core processors combined with some innovative motherboards make the commodity proposition a very real alternative to the high end server hardware. Enough talk, let's get to the results because they tell the real story.

Pentium D You Say?

For the tests, I used the recently introduced 3.2 GHz Pentium D (Presler) processor from Intel (which will eventually be replaced by the Xeon 3000 line). The Presler series is a dual-core processor manufactured using the latest 65nm process and is currently available at speeds up to 3.40 GHz. More importantly for HPC users, each Presler has 4 MB of on-chip cache which it divides evenly between the two cores (2 MB each). These caches are fed using an 800MHz FSB and DDR2 memory. We used eight of these to create a 16 core cluster.

Dangerous Assumptions

As a way to introduce the results, lets look at some of the assumptions currently floating around the HPC market, but first the standard advisory. As with all things cluster, performance depends on your application. If your application(s) do not behave like the benchmarks, then you may want to do your own testing. In my testing, I used the NAS Parallel Benchmark Suite and the GROMACS Molecular Dynamics package. You also may want to look at Parallel Molecular Dynamics: Gromacs by Erik Lindahl.

The cluster consisted of eight Pentium D 940 (3.2 GHz) processors (16 cores total), one per motherboard, connected with an SMC 8 port gigabit Ethernet switch. (See the Testing Methodology Sidebar at the end of the article for more information.) Based on my testing, the following assumptions may be worth checking:

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