cdrom access w/o dma produces system load around 10

I have an atiixp based system (MSI RS480M2) running in 64 bit mode, using breezy. DMA is off by
default for the cdrom/dvd drives. While in it's default post-install configuration (if I don't
use hdparm to turn dma on), system load will go to 10 when copying from cdrom to hard disk. It
doesn't matter which disk drive I'm using, same effect.

When I turn dma on, that load drops down to 0 effectively.

Now I understand why dma is not currently on by default, BUT there has to be a solution for this.
A computer shouldn't have to wait anymore on disk io, but it freezes the desktop, stops music
players, etc. making the system unusable whenever any cd/dvd activity is happening (plus the dvd
burner runs at 0.7x with dma off).

This is similar to bug: 3672, but there could be another issue at hand here specific to the atiixp
chipset and/or amd64, since a load of 10 seems unusual.