Get to Know Conky

While Ubuntu/Gnome/Compiz offer various widgets to monitor computer activity, I think they tend too much to offer a strong visual effect rather than actual useful, structured, information about what’s going on in your computer. Sometimes, it doesn’t really matter. Sometimes you want to know more.

One tool that’s not the mega-eye-candy but is very configurable and actually useful is Conky, a “free, light-weight system monitor for X, that displays any information on your desktop.”

The CFM-01

In a previous post, I presented the CFM-00, a “cluster” of 8 Pentium III at 500MHz, assembled into one MDF casing. The assembly was rather clean-cut given the rather rudimentary materials (MDF and threaded rods) but the resulting computing power is dismal (but that’s no surprise). We have about 2GHz of computing power, and at 128MB of ram per node, it makes running even just a remote shell not that responsive.

A few months ago, my friend Christopher came to me with a data center clearing deal with Pentium III 1GHz 1U rack-mount (with 512MB of RAM) servers for $15, and I got eight of them to build the CFM-01, the successor to the CFM-00. But I did not strip the motherboards from their casing this time, I built an inexpensive rack out of slotted angle steel.

The Perfect Instruction Set

The x86 architecture is ageing, but rather than looking for re-invention, it only saw incremental extensions (especially for operating system instructions and SIMD) over the last decade or so. Before getting to the i7 core, we saw a long series of evolutions—not revolutions. It all started with the 8086 (and its somewhat weaker sibling, the 8088), which was first conceived as an evolutionary extension to the 8085, which was itself binary compatible with the 8080. The Intel 8080’s lineage brings us to the 8008, a 8 bits of data, 14 bits of address micro-processor. Fortunately, the 8008 isn’t a double 4004. The successors of the 8086 include (but the list surely isn’t exhaustive) the 80186, the 80286, the 80386, first in the series to include decent memory protection for multitasking, then the long series of 486, various models of Pentium, Core 2 and i7.

So, just like you can trace the human lineage to apes, then to monkeys, and eventually to rodent-like mammals, the x86 has a long history and is still far from being perfect, and its basic weakness, in my opinion, is that it still use the 1974 8080 accumulator-based instruction set architecture. And despite a number of very smart architectural improvements (out of order execution, branch prediction, SIMD), it still suffers from the same problems the 8085 did: the instruction set is not orthogonal, it contains many obsolete complex instructions that aren’t used all that much anymore (such as the BCD helpers), and that everything has to be backwards compatible, meaning that every new generation still is more of the same, only (mostly) faster.

But what would be the perfect instruction set? In [1], the typical instruction set is composed of seven facets (to which I add an eighth):

Patching the Environment for ‘exotic’ Libraries

Every time I add a development library (or any other application) that is not found in my distro‘s repositories, I ask myself how troublesome it will be. If you’re really lucky, it comes in a package (and repository) compatible with the target distribution (like a Debian package or a RPM) and everything is just fine: you install it from the package manager, and that’s it. But if not, you have to download a tarball from some (more or less trusted) location like Sourceforge. It usually comes with a rather well designed set of configure, make, and (sudo) make install scripts that reduces configuration to little more than launching the configuration script, check for any unmet dependencies, add them and rerun the configuration script until they are all met, and then make install performs a smart, standard location install and you’re done. You won’t have the automagical upgrades with everything else, but you can go on with your life.

Then again sometimes you have to install a library (or application) that either has a half-baked installation script, or is incompatible with your distro, or, cerise sur le gâteau, both. And, just to aggravate you just fine, it installs to a non-standard location requiring you to specify include and library paths in your make files or just to invoke the application. And, of course, default location will change from from /usr/local/shared/thislib/ to /usr/shared/include/thislib between version 2.1.5 and 2.1.6, just to make sure to break just about everything you set up.

Damn you, Saint-Exupéry!

The Ubuntu Linux distribution is putting a lot of efforts into streamlining the interface and provide a greater user experience. While there’s clear progress, there are a number of things that are still really missing. The guys at Gnome and at Ubuntu are maybe taking the motto perfection is not when there’s nothing else to add, but nothing else to remove a bit too seriously. Every release shows more and more features but less and less user configurability.

Well, to be honest, I have always found my way around those limitations by hacking directly configuration files, the gconf-editor registry-like thingie, and writting scripts to set automatically configurations for which there were no other way—or just not documented, which is the same as far as I am concerned.

Amongst the extra thingies, there are many keyboard shortcuts, but not all of them are configurable. For example, if there’s a way from Gnome to configure which keys you want to use to control LCD or keyboard brightness or to display power information, it’s pretty damn well hidden. On my Dell mini, there’s a nice key with a battery icon on it. If I press it, Gnome displays in the OSD a concise battery status. But on my macbook pro, there’s’nt such a key and I have no way of telling Gnome (from Gnome itself) to use the F4/Gauge key to act as the Show Battery key.

Suggested Reading: Patterns for Parallel Programming

Timothy G. Mattson, Beverly A. Sanders, Berna L. Massingill — Patterns for Parallel Programming — Addison-Wesley, 2005, 356 pp. ISBN 0-321-22811-1

(Buy at Amazon.com)

If the Gang of Four changed the way we discuss about software design by introducing a catalogue of basic software patterns, this books vies to extend it to parallel patterns. But let us be clear, it’s not a book about parallel algorithms; no, it discusses parallelism in very general terms and present the few prototypical application types and how they can be efficiently broken down by data structure, command flow, and synchronisation, while remaining rather high level.

Upgrading to Lucid Lynx

Every once in a while, if you’re not using a rolling release distro like, say, Arch Linux, you have to dist-upgrade your machines. Dist-upgrading consist in upgrading pretty much everything on your computer to the new version sets that correspond to the next distro. I just upgraded from Koala to Lynx.

And, well, …

The CFM-00

Parallel computing is the next paradigm shift, everybody knows this, but not everyone is taking the proper action to face it adequately. One thing to do is to read on the subject and force oneself to code using threads and various degrees of parallelism; and that’s pretty easy now that a quad core machine doesn’t cost all that much. But the next step, distributed computing, necessitates, well, more than one machine, and if you have different levels of memories and communication channels, all the better.

So out of a bunch of old x86 PCs, I’ve decided to build my own portable mini-cluster with 8 nodes. Nothing all that impressive, but still plenty of fun to build.

Leafing Through Old Notes

Leafing through old notes, I found some loose sheets that must have been, at some time, part of my notes of my lectures on external data structures. I remember the professor. He was an old man—I mean old, well in his 70s—and he taught us a lot about tapes and hard drives and all those slow devices. As a youth, I couldn’t care less about the algorithms for tapes, but in retrospect, I now know I should have paid more attention. So, anyway, the sheets contains notes on how to compute average rotational latency and average (random) seek time.

Suggested Reading:Unix Systems for Modern Architectures

Curt Schimmel — Unix Systems for Modern Architectures: Symmetric Multiprocessing and Caching for Kernel Programmers — Addison-Wesley, 1994, 396 pp. ISBN 0-201-6338-8

(Buy at Amazon.com)

Schimmel proposes an introduction to cache hierarchies and their different technologies and the problems and complexities they incur for an operating system. The book starts off by presenting and comparing the various cache architectures—physical vs virtual caches, mostly. Another part is dedicated to the various locks and exclusion mechanisms such as spin locks, semaphores, etc., that may be found in Unix-type systems. He finishes with cache consistency problems for multiprocessors.