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.
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.
Ingo Molnar has been contributing to Linux kernel development since 1995 with an impressive list of accomplishments. Most recently his O(1) scheduler was merged into the 2.5 development kernel, as well as much work to enhance the handling of threads. Other highly visible contributions include software-RAID support and the in-kernel Tux web and FTP servers.
In this interview, Ingo explores how he started working on the Linux kernel noting, "it might sound a bit strange but i installed my first Linux box for the sole purpose of looking at the kernel source." He goes on to explain the concepts behind his new O(1) scheduler, and to describe many of his other kernel efforts. This interview was conducted over several months, and covers a lot of interesting ground...
A recent lkml thread explored an interesting tangent when Jeff Garzik asked about what was to follow the 2.5 development kernel, "is it definitely to be named 2.6? Maybe it's just my impression from development speed, but it felt more like a 3.0 to me :)". Linux creator Linus Torvalds first suggested that there was no reason to skip from 2.5 to 3.0, qualifying it with, "But hey, it's just a number. I don't feel that strongly either way."
Ingo Molnar reflected on the significant improvements we've seen to the VM and the IO subsystem, going so far as to say, "I think due to these improvements if we dont call the next kernel 3.0 then probably no Linux kernel in the future will deserve a major number. In 2-4 years we'll only jump to 3.0 because there's no better number available after 2.8."
Linus agreed that if the VM is as good as it seems to be, indeed the upcoming release deserves to be called 3.0. But he also pointed out that there are many silent users who tend not to speak up until there is an official release. He asks, "people who are having VM trouble with the current 2.5.x series, please _complain_, and tell what your workload is. Don't sit silent and make us think we're good to go.. And if Ingo is right, I'll do the 3.0.x thing."