Dear Cafe, with +RTS -p -RTS, the resulting .prof file shows (in the second part) what the expensive functions are. (counting sections as GHC docs do - first part gives program name and options) Often, that's useful, but sometimes, this info does not surprise me - some things just don't have an easy implementation. For those, I want to find out who calls them - to possibly replace some of these calls with a cheaper implementation (that is only valid because the caller knows something that the callee does not) Is there some automation for getting this information? I am not even sure how to formalize what I want. Perhaps, for the first N heavy cost centers (SCCs), a suitably ordered list of their callers (that inherit the cost)? The data is in the third (long, detailed) part of the .prof file but I find it hard to process (in that form). It represents the call hiearchy by indentation (first column) and adjacency (of rows) but this goes out the window as soon as I grep or sort the rows. The JSON output format seems the way to go https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/profiling.ht... . Yeah, I should probably just aeson it and then walk the tree. I still wanted to ask for advice first, or references to existing work. Any pointers appreciated. - J.