[Haskell-cafe] Problems with threading?

Isaac Gouy igouy2 at yahoo.com
Mon Jun 7 19:38:43 EDT 2010

--- On Mon, 6/7/10, Don Stewart <dons at galois.com> wrote:

> From: Don Stewart <dons at galois.com>
> Subject: Re: [Haskell-cafe] Problems with threading?
> To: "Louis Wasserman" <wasserman.louis at gmail.com>
> Cc: "Haskell Café List" <haskell-cafe at haskell.org>
> 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
> > 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.* :-)

> > 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



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. 


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