Cabal: How to profile?

[jrp2014]

Perhaps this is a documentation issue, but when I run something like cabal v2-bench --enable-profiling the benchmark runs, but produces no profiling output that I can see. If I run with cabal v2-run +RTS -p I get the the flag -p requires the program to be built with -prof error. Perhaps the bench and run executables are pointing at different things and perhaps the profiling output is buried somewhere, but the out of the box experience is suboptimal.

[hvr]

It's quite simple actually :-)

There's two ways of operation here: either you can operate in the non-stateful way, then you need to explicitly pass the --enable-profiling to every cabal command which is able to compute an install-plan, i.e.

cabal v2-run --enable-profiling exes --  +RTS -p

or you can persist those settings by invoking

cabal v2-configure --enable-profiling

which will merely create a file cabal.project.local with the single line

profiling: True

and then you don't need to explicitly pass --enable-profiling anymore via the CLI.

I hope this clears this up. Feel free to ask follow-up questions if something's still unclear.

[jrp2014]

Many thanks, Herbert. That makes sense. (It would be good if the cabal documentation made the basic conventions clear; they seem obvious once they are explained but the cabal manual doesn't do a great job of explaining the underlying concepts (eg, when to drive and persist through the command line and when to put things into the cabal file).

[hasufell]

This doesn't work for me. I built with the following config:

library-profiling: True
profiling: True

package *
  ghc-options: -O2 -threaded -fprof-auto "-with-rtsopts=-N -p -s -h -i0.1"

When running the executable with +RTS -p -RTS it errors out with the flag -p requires the program to be built with -prof. If you do what it says, you get the problems described in https://github.com/haskell/cabal/issues/2827

Edit: I'm using cabal v2-install and then run the exe directly.

[Achierius]

Same issues as @hausfell; I'm building for Windows, and I've tried a few permutations of the ghc-options listed above without luck.

[hasufell]

@Achierius did you try to run cabal v2-build instead and then manually copy the binary? I consider v2-install broken by now (for installing local packages), because it ignores project files, afais.