Fear and paranoia

A great statement on the state of paranoia and fear we currently live in:

More (semi-)useless knowledge

Only non-royal eight Britons have been given state funerals. Among them are Winston Churchill (the Prime Minister during World War II); Arthur Wellesley, 1st Duke of Wellington (commanding general at the Battle of Waterloo); and Horatio Nelson, 1st Viscount Nelson (commanding admiral at the Battle of Trafalgar). The strange things you learn reading late at night...

The value of a good compiler

In the process of installing a new compute cluster at work, I evaluated several compilers and was surprised at how well Intel's compiler (icc) performs. This was made apparent by some of the results I obtained from the Scimark2 benchmark, as shown below.

The graph shows the MFLOPS measured by each of the Scimark2 computational kernels on three different machines:

• A Dell PowerEdge 6650 with 4 Intel Xeon MPs (32-bit, hyperthreaded, 2.0-GHz);
• A Sun X200 M2 with 2 AMD Opteron 2200s (64-bit, dual core, 2.8-GHz); and
• A Dell PowerEdge 2950 with 2 Intel Xeon 5130s (64-bit, dual core, 2.0-GHz)

The 32-bit version of Scimark2 was compiled using version 10.0 of the Intel C++ compiler, while the 64-bit version was compiled using gcc 3.4.6 (the default compiler with the Rocks 4.3/CentOS 4.5).

Not surprisingly, the 64-bit machines perform better on the whole, as evidenced by the scores for the "Composite", "FFT" (fast Fourier transform), "SOR" (Jacobi successive over-relaxation), and "LU" (dense matrix LU factorization) computational kernels. What is surprising, however, is that the five year old PowerEdge 6650 using icc actually managed to outperform the shiny new 64-bit machines using gcc. I haven't looked in detail as to why this happens. However, based on the descriptions of the benchmark kernels, I suspect much of the performance gain comes from the Intel compiler being much better at managing certain types of memory operations.

RIP: John Wheeler (1911 - 2008)

The New York Times has an article on the life and death of John A. Wheeler. Over at Cosmic Variance, Daniel Holz offers an excellent personal tribute to one of the great physicists of the last century. Dave Bacon (The Quantum Pontiff) offers another remembrance of Wheeler and the impact he had in the world of physics.

For my part, Misner, Thorne, and Wheeler's book Gravitation remains close to the top of my list of books I should get around to reading.

Quote of the day

Seen on the Rocks clusters mailing list: "A supercomputer is a device for turning compute-bound problems into I/O-bound problems."¹ So true.

¹ Credited to either Seymour Cray or Ken Batcher, depending on who you ask.