Continuing the earlier discussion about low latency and Ingo Molnar [interview]'s voluntary kernel preemption patch [story], the conversation moved onto the affect a filesystem can have on latency. Specifically, 2.6 maintainer Andrew Morton [interview] noted that ReiserFS was known to have some latency issues in both the 2.4 and 2.6 Linux kernels, "resierfs: yes, it's a problem. I 'fixed' it multiple times in 2.4, but the fixes ended up breaking the fs in subtle ways and I eventually gave up." However, he did go on to note, "actually, the 2.4 low-latency patch does still have some reiserfs fixes, so it's probably better than reiserfs in 2.6."

When asked if ext3 was a better choice for low latency work, Andrew Morton replied, "ext3 is certainly better than [reiserfs], but still has a couple of potential problem spots. ext2 is probably the best at this time." Data is continuing to be collected and reviewed by a number of kernel developers, so the more noticeable latency issues in the 2.6 kernel will likely be addressed soon.

Andrea Arcangeli is well known for having completely rewritten and stabilized the virtual memory subsystem in the 2.4 Linux kernel. Many were surprised when Linus Torvalds merged Andrea's VM into 2.4.10, but the new memory subsystem has long since proved itself. Andrea is a 27 year old Linux kernel hacker living in Italy and working for SUSE.

Anyone who's been following Linux kernel development for the past several months has heard about one exciting feature after another being merged into the still un-released 2.6 kernel. New features that noticeably affect user experience include Robert Love's [interview] preemptible kernel work [story], Ingo Molnar's [interview] O(1) Scheduler [story], Rik Van Riel's [interview] reverse mapping VM [story], Nick Piggins' [interview] Anticipatory I/O scheduler [story], and much, much more...

Having some spare time a few nights ago, I decided to give the latest kernel, 2.6.0-test4, a trial run on my aging 550Mhz PIII desktop computer, and the result was nothing short of spectacular. As the final 2.6.0 release approaches, it is important that an increasing number of users (aka testers) give this kernel a try, especially as currently it's still a sexy task for developers to track down kernel bugs and stabalize their work. Once work starts on the 2.7 development tree, inevitably much talent will again be focusing on new features.

The purpose of this document is to provide some helpful tips to readers that currently compile their own 2.4 kernels, but haven't yet made the leap to 2.6. This is still a development kernel, so you may run into problems, but overall stability and performance is quite impressive and I can't recommend enough that you try it today.

Con Kolivas, a practicing doctor in Australia, has written a benchmarking tool called ConTest which has proven to be tremendously useful to kernel developers, having been designed to compare the performance of different versions of the Linux kernel. He was kind enough to speak with us, explaining how he got started on this project, what makes his benchmark unique, and how to interpret the resulting output. Comparing the 2.5 development kernel to the 2.4 stable kernel, Con says, "a good 2.5 kernel (and that's not all of them) feels faster than 2.4 in most ways and this bodes well for 2.6." The interesting results from his frequent benchmarks back up this statement.

Con also describes his high performance patchset for the 2.4 stable kernel, currently at version 2.4.19-ck9. This patchset adds a number of performance boosting patches ideal for a desktop environment, such as the O(1) scheduler, kernel preemption, low latency and compressed caching. Read on for the full interview...