Tips for tweaking your kernel.

How can I make my kernel boot faster?

If you remove things you dont need from the kernel, like SCSI support if you dont have SCSI devices and wont ever want to use a USB Mass Storage device such as a Digital Camera, you end up with a smaller kernel - which will in turn boot faster. I've not measured how much benefit you get from this however

How can I improve performance on a desktop machine? (or on a slower machine)

There's a handful of patches for the 2.4 kernel series which attempt to address some of the scheduling slowdowns seen in the Linux kernel.

LowLatency

The LowLatency patch reduces the kernels scheduling latency, which should improve performance. Here's another howto on ALSA and LowLatency. Most recent patch is for 2.4.21.

I've not used this one myself, so I can't guarantee how well it will work for you. A lot of people seem to like it however.

Pre-emptive Kernel

This patch improves the pre-emptive properties of the kernel. See KernelPreemption for more notes on what this means. It can be found at a KernelMirror near you. Most recent patch is for 2.4.21.

I have used this patch on an HP Vectra (233 MHz P2, 32 MB RAM), to fix skipping mp3s when playing via XMMS locally, or XMMS remotely + ESD locally, and running remote X. This is a fairly slow machine by todays standards, and was seeing a lot of interrupt activity - lots of network, sound, and video changes. I would get nasty crackles in the mp3s if i changed virtual desktops and a large screen redraw was needed - the preempt patch fixed this.