Hello, I'm using ghc 6.6.1 under Ubuntu Gutsy on a Pentium 4 machine, and I was working to get some code running in an acceptable time. I was surprised to find that turning on profiling switches made the code run over 40x faster! Here's the first run, using ghc --make -O2: 88.03user 0.08system 1:28.16elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+13517minor)pagefaults 0swaps And with ghc --make -O2 -prof -auto-all: 2.33user 0.07system 0:02.41elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+17712minor)pagefaults 0swaps Otherwise everything is the same! Is this something anyone else has run into? I'm not sure if it might have been fixed in 6.8.1, but something funny is going on here. Thanks, Chad