[Haskell-cafe] Haskell Speed Myth

[Don Stewart]

igouy2:
> otoh I see the attraction of showing parallelised versions alongside
> existing programs; otoh that adds yet another layer of confusion about
> why the measurements differ (and another level of quarreling about
> whether even vaguely the same thing is being measured); otoh some
> existing programs already use more cores when they can ...
> 
> The Scala threadring program shows 524s cpu but 157s elapsed:
> 
> http://shootout.alioth.debian.org/u64q/benchmark.php?test=threadring&lang=all

Very cool!
  
> > I'm keen to get going on this, if only because I think we can turn
> > out parallelised versions of many of the existing programs, fairly
> > cheaply.
> 
> I'm always delighted that you're keen to get going on things like this!
> 
> The benchmarks game always seems to demand somewhat unnatural acts and
> here's another - is there an effective way to /prevent/ ghc using
> multiple cores when multiple cores are available? Can we force ghc to
> only use one core on the quadcore machine? (Moreover can we do the same
> trick for other languages?)

Certainly, for the quad core, to get all 4 cores in play:

    * compile with -threaded
    * run with +RTS -N4

to force single core, we'll:

    * compile normally
    * run normally

-- Don