Re: [Haskell-cafe] Problems with threading?

--- On Mon, 6/7/10, Don Stewart wrote:

From: Don Stewart Subject: Re: [Haskell-cafe] Problems with threading? To: "Louis Wasserman" Cc: "Haskell Café List" Date: Monday, June 7, 2010, 2:50 PM wasserman.louis:

...

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

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

Using -N5 sounds suspicious. There are only 4 cores on the machine.

-N5 is likely to have been your orsuggestion for getting the most out of ghc 6.10.* :-)   -snip-

...

I wanted to throw this out for people to discuss, because I'd like to see it improved.

As Louis has already mentioned this to me, I'll take the opportunity to sketch out a simple approach - 1) GHC programs compiled without -threaded and run without +RTS -N are already shown for x86 and x64 http://shootout.alioth.debian.org/u32/compare.php?lang=ghc http://shootout.alioth.debian.org/u64/compare.php?lang=ghc 2) For quad-core, the GHC programs will all be compiled with -threaded and all run with +RTS -N4 3) That seems to match the approach taken with Erlang, where all the programs on quad-core run with smp built into the vm, and all the programs on one core run without smp built into the vm.