Simon Peyton Jones via Haskell-Cafe
Compl’s problem is (apparently) that execution becomes dominated by GC. That doesn’t sound like a constant-factor overhead from TVars, no matter how efficient (or otherwise) they are. It sounds more like a space leak to me; perhaps you need some strict evaluation or something.
My point is only: before re-engineering STM it would make sense to get a much more detailed insight into what is actually happening, and where the space and time is going. We have tools to do this (heap profiling, Threadscope, …) but I know they need some skill and insight to use well. But we don’t have nearly enough insight to draw meaningful conclusions yet.
Maybe someone with experience of performance debugging might feel able to help Compl?
Compl, If you want to discuss the issue feel free to get in touch on IRC. I would be happy to help. It would be great if we had something of a decision tree for performance tuning of Haskell code in the users guide or Wiki. We have so many tools yet there isn't a comprehensive overview of 1. what factors might affect which runtime characteristics of your program 2. which tools can be used to measure which factors 3. how these factors can be improved Cheers, - Ben