I'm having trouble getting decent speeds out of Jgarzik's miner on Ubuntu 10.10 (Phenom II X4 920). I'm only getting 125 kh/s per thread (4 threads), which drops to 50 kh/s with 4way enabled.

The same computer does 10+ mh/s using ufasoft's Win SSE2 miner.
Can someone please enlighten me as to how I can get the same performance under Linux.