On 19/02/2011 04:57 PM, Edward Amsden wrote:
But note that with GHC 7.x, the RTS *automatically* chooses the correct
number of threads now. You no longer need to specify this manually (unless
you specifically want to use some other number of threads for some reason).
Is that stated in the changelog or documentation somewhere? Do you
still have to specify -threaded at compile-time?
You most definitely have to specify -threaded at compile-time; that
selects the threaded RTS. (Otherwise you get the non-threaded RTS, which
*always* uses 1 thread.)
This much was always true; what is new is that the threaded RTS used to
default to still using only 1 thread. Now it defaults to using a number
of threads that is determined by how many CPU cores you actually have.
(I'm not sure if it uses N cores or N-1 cores; I seem to recall that
using *all* cores caused a slowdown on some systems. I don't know if
that's fixed now...)
I don't see this mentioned in the release notes, but it's definitely in
the RTS flags documentation.
http://haskell.org/ghc/docs/7.0.1/html/users_guide/using-smp.html#parallel-options
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