[Solved] The -N RTS option is not documented in the GHC manual

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Hi!
While re-learning async (great stuff btw!) I just noticed that the -N options, controlling the number of physical threads to be used by the RTS, is not listed in the manual:

https://downloads.haskell.org/ghc/latest/docs/users_guide/runtime_control.html

It’s only mentioned by other flags, but not documented per se, we can only read about it in various stackoverflow comments.

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Isn’t it here?

https://downloads.haskell.org/ghc/latest/docs/users_guide/using-concurrent.html#parallel-options

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Ah, I was looking in the wrong place, thanks @LaurentRDC !

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Hmmm I never had to debug a problem like that. Can you tell us more about the computation?

Is it embarassingly parallel? How long do threads live? Is FFI involved?

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Thanks for following up!

after a little printf debugging I saw I was simply feeding it too few tasks at a time. Completely parallel, no data dependencies not even MVar/transactional, no FFi, just rejection sampling a lot of random structures under different conditions and streaming to disk.
Now it’s burning rubber on all 64 cores, happy times.

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