High %wa, irregular blocking

[b-misc@gmx.ch]

Hi,

Some weeks ago I installed Testing on my wife's iMac [1] from 2008.
Unfortunately it has one issue:

There are irregular periods of very high %wa, maybe 3-5 times per hour, not
directly related to a certain user action. They last for some seconds up to
even a minute or so and render the machine unusable for that time. top shows %wa
of 80 or 90%, load can go up to 9 on this dual core machine, iotop shows only a
few KB/s.

I already added pcie_aspm=off to the boot options which seems to help,
but I still see this I/O hangs (without, I had about 10+ hangs per hour).

Any idea what could cause these blockings? How can I find out more? I use Linux
for 15+ years but I never saw such things... and I want to show my
wife, that Linux is the better OS, of course... ;-)

Aside from that issue everything runs quite nicely.

Thanks & best regards,
Bernd

[1] iMac 8,1: 2008, Core 2 Duo 2.8 GHz, GB RAM, 500 GB WD HDD, ATI Radeon HD
2600 PRO (PCIe)