Tuning GHC's Runtime System

GHC's Runtime System is not something that could be called elegant, consisting of 50,000 lines of C and C-- (a C-like language) code that does a lot of managerial things to execute compiled Haskell programs. The RTS is responsible for managing exceptions, implementing GHC's primitive functions (those suffixed with a magic hash), and scheduling light-weight threads. Memory management, profiling facilities, and STM are all implemented in RTS, and more.

How is this relevant to a Haskell programmer? Knowing the scope and limitations of the RTS is one thing. Also, the RTS isn't so much a black box; it can provide useful feedback about running programs, such as memory usage, garbage-collection statistics, profiling information, and so forth. Many aspects of the RTS are configurable via flags, whose optimization is necessary to max out performance. Different applications utilize the RTS in wildly different ways.

Runtime System flags are set at program startup:

./program...