[Fedora-xen] understanding perfomance

[Ben]

I'm having a hard time understanding how to determine load on my  
domUs. I'm running FC5 on both my dom0 and domUs, all up to date  
against the official fedora repositories as of last night. On at  
least one of my domUs acting as a database, xm top shows CPU load at  
roughly 60% when I fire off some long-running queries. That sounds  
reasonable to me, but running top of the domU itself shows almost no  
cpu load. The domU *is* doing a lot of I/O, but according to vmstat  
on the domU, very little of the processors are stuck in I/O wait state.

So, I'm not sure what the proper question is. It's probably some  
combination of these two:

1. Why does the domU not think it's stuck in I/O wait?
2. Why does xm top and top on the domU disagree?