Ever since I started using Xen 3.0 I had a feeling disk access to my primary IDE harddrive was dreadfully slow. But as I'm running 9 domains on this one machine I thought it might be normal for the load I am putting on the system.
During a free slot this week I did some searching and found some reference to IDE DMA being disabled. I checked my disk with hdparm and sure: No DMA support. It must have been somewhere in the last century that I manually set anything in Linux for my IDE controller. Untill recently it always 'just worked'™
So today I did a recompile of the kernel, leaving generic IDE support out and only enabling the VIA IDE drivers. This took forever, because well, DMA was still disabled at this time.
A very long reboot later, DMA was enabled and this piece of silicon is flying again.
TODO: fix some startup script in some of the domains ;)