Exascale Computing

Recently, I heard David Keyes talk about exascale computing ("Exaflop/s Seriously!"). There were two interesting lessons.

1. In one of his viewgraphs (which I unfortunately do not have access to) he plotted the peak performance of the top supercomputer in the Top500, versus time. The resulting curve looks familiar (Moore's law), and when drawn on a log-linear scale looks approximately linear. I reproduce a similar looking curve (but this one combines all the 500 top machines) below.

The interesting part of the viewgraph was that, on the same plot, he also threw in the performance of the 500th best machine in the Top500. This was also linearly increasing (on a log linear plot) curve that lay somewhat lower than the fastest computer.  The surprising bit (for me at least) was that the "phase shift" in terms of time was about 8 years. That is, if the top machine in the Top500 was left alone, in 8 years it would be overtaken by everybody else in the elite group.

This can have policy implications for HPC centers. Rather than trying to build the fastest computer now, perhaps, having a long-term plan to keep upgrading the system is more important.

2. We've seen CPU clock cycles stagnate. For HPC centers, which use thousand of them, energy considerations can quickly become the dominant concern. This explains the shift to multicore. I learned that energy scales roughly as the third power of the frequency. From here, for example

"If the clock rate of the Multi-Core CPUs will be reduced by 20% only, then the energy consumption is reduced to 50% compared to a system running at full clock speed.”

On the other hand, for multicore CPUs the energy is only proportional to the first power of the number of cores, explaining the move towards multicore, low frequency supercomputers. I don't know if the numbers here include the cost of air-conditioning (I presume they do), but they can be a significant operating cost.

I remember that we had a small Beowulf cluster (puny by today's standards), when I was in grad school, that was housed in a student office for sometime. The room was unbearable in summer.

Paper or On-screen reading?

I spend a significant fraction of my waking life reading. About ten years ago, most of my reading, and writing for that matter, was paper-based.

I distinctly remember that during my senior thesis, and the first few years in grad school - I couldn't read and think, off a computer screen at all. Writing was even harder, and I used to write stuff down on paper before composing a serious document.

Any technical paper, I had to download, print, and scribble on to really digest.

Here are articles from the Boston Globe and a University of Florida website which support the thesis that reading from paper is better. The latter website claims reading paper is 20-30% faster, more accurate (in terms of the ability to identify grammatical and typographic errors), and less taxing on the eyes.

But things change.

Personally I can now read much better off a screen. With a high-resolution monitor, I prefer it. My main reasons are the following:

1. zoom
   
2. place my paper online, and read it from any computer.
3. "Go Green"
4. read and create color documents at no additional cost
5. follow hyperlinks
6. organizing/searching papers is easier 
7. search for a word in a long document

In fact, I write much better on a keyboard too. Not only has my speed increased, I can correct spelling errors, and especially because I use a sophisticated word processor invented in the 70s called LaTeX, I worry less about appearance and more about content.

Indeed, a not-so-new paper cited at the end claims that paper and on-screen reading have now become equivalent.

Something that my own experience mirrors.

Reference:

Harrison, B, ‘E-Books and the Future of Reading’, IEEE Computer Graphics and Applications, Volume 20 , Issue 3 (May 2000) , pp. 32 - 39.