[Haskell-cafe] Problems with threading?

[Louis Wasserman]

While working on the Shootout, I noticed the following benchmarks:

http://shootout.alioth.debian.org/u64/program.php?test=chameneosredux&lang=ghc&id=3
<http://shootout.alioth.debian.org/u64/program.php?test=chameneosredux&lang=ghc&id=3>
http://shootout.alioth.debian.org/u64q/program.php?test=chameneosredux&lang=ghc&id=3

The same program becomes almost 4 times slower when compiled with --threaded
and run with +RTS -N5 -- even though the multi-core benchmark really only
ever uses one processor.

Other languages seem to have found a way of arranging these threads in a way
such that parallelism actually happens, but as it stands, compiling this
benchmark without --threaded actually makes Haskell competitive against the
genuinely parallel alternatives in other languages...which is unusual by
itself.

I wanted to throw this out for people to discuss, because I'd like to see it
improved.  As it stands, I'm going to submit a version which asks not to be
compiled with --threaded (and has a few other improvements).
<http://shootout.alioth.debian.org/u64q/program.php?test=chameneosredux&lang=ghc&id=3>
Louis Wasserman
wasserman.louis at gmail.com
http://profiles.google.com/wasserman.louis
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