wiki:Debugging/TickyTicky

Version 2 (modified by simonpj, 4 years ago) (diff)

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Ticky-ticky profiling

Ticky-ticky profiling adds counters to every STG function. It's very low-level, but it really tells you what is going on:

  • Add the -ticky flag when compiling a Haskell module to enable "ticky-ticky" profiling of that module. This makes GHC emit performance-counting instructions in every STG function.
  • Add -debug to the command line when linking, so that you link against a version of the runtime system that allows you to display the results. [Adding -ticky should work too, but it doesn't yet.]
  • Add +RTS -rfoo.ticky to the run-time command line, to put the ticky-ticky profile in the file foo.ticky.

It's very low level stuff. You need to use -ddump-simpl -ddump-prep when compiling the source files to see the functions that correspond to the performance counter report.

You can mix modules compiled with -ticky and modules compiled without.

To really see everything you need to compile all the libraries with -ticky. To do that in a standard build tree, here are some flag settings in build.mk that work:

# Build all libraries with -ticky
GhcLibOpts += -ticky

# Build the RTS in the ticky way
GhcRTSWays += t

# Currently ticky is incompatible with threading
GhcThreaded = NO

# When linking stage2 you need -ticky, else you get unresolved symols
GhcStage2HcOpts += -ticky

# Ditto Haddock
utils/haddock_dist_EXTRA_HC_OPTS += -ticky

But see #3439, which would allow you to drop the last two.