I got some very nice help from Diablo-D3 among others over IRC yesterday, but so far this is unresolved. I recently got a 5970 in my workstation, earlier running Debian sid with 2.6.37. Since 10.12 (latest available catalyst) didn't support 2.6.37 I went back to the squeeze kernel (2.6.32) and started running the diablo miner. This worked just fine and got full load on both GPUs directly. So that was using Linux 2.6.32, Catalyst 10.12 and AMD APP SDK 2.1.

Crossfire was reported as on in aticonfig --lscs and off in aticonfig --lsch, but since it worked I payed it no mind.

Yesterday I thought I'd try 11.1, since it at last brought support for my normal kernel (2.6.37). So I installed it, and thought I'd continue business as usual. But alas! The CPU now had a 50% load (dual core, so 200% is full load) and the GPUs were only working in 60-70% load according to aticonfig --odgc, and the hashes/s dropped accordingly.

I tried reverting to 10.12 and 2.6.32, but the problem only got worse. CPUs in full load and even lower GPU load. After this I've tried basically all combinations of Catalyst 10.9 and up, supported kernels and SDK 2.1 and 2.3. What works best right now is 2.6.37, 11.1 and SDK 2.3, but its close to half the speed of what I had before the change.

I tried installing a fresh Debian squeeze on a extra disk, with SDK 2.1 catalyst 10.12 and 2.6.32. A bare X and Diablos miner. Same problem! So its not just a problem with my current install, but more with the behavior of my graphics card. Can 11.1 have effected some fuse causing all this?

And no matter what I do with aticonfig and crossfire the result is the same. But I can get either enabled/disabled or enabled/enabled on --lscs/--lsch

Last, I also tried poclbm and this can just use one core at a time, if I start one process on GPU2 and then the other one on GPU1 both get on GPU2, reverse the order and both get on GPU1. At one time I got it to run on both GPU cores, but 100% load on the first and low single digit % on the second.

Anyone else with experience with either 11.1 or HD 5970 that can be of assistance?

Yes, the DISPLAY environment variable was set. As I said the same configuration has run flawlessly before, and trying with two installations. What does --lscs and --lsch say for you when you have it working?