[Haskell-cafe] Significant slow-down in parallel code?

Hello; I have a piece of code in which I employ the `par` construct to add some implicit parallelism to a theorem prover. However, when running the *same* code with +RTS -N1 +RTS -N5 +RTS -N10 I see a huge slowdown (a factor of 50 with 5 processes and a factor of 100 for 10 on an 8-core machine). Very little time is being spent using the garbage collector. Any suggestions? Thanks, -Jamie