[Haskell-cafe] Haskell Speed Myth

Thomas M. DuBuisson thomas.dubuisson at gmail.com
Tue Aug 26 02:02:59 EDT 2008

> Simon Marlow sez:
>     The thread-ring benchmark needs careful scheduling to get a speedup
>     on multiple CPUs. I was only able to get a speedup by explicitly
>     locking half of the ring onto each CPU. You can do this using
>     GHC.Conc.forkOnIO in GHC 6.8.x, and you'll also need +RTS -qm -qw.
>     Also make sure that you're not using the main thread for any part of
>     the main computation, because the main thread is a bound thread and
>     runs in its own OS thread, so communication between the main thread
>     and any other thread is slow.

I had to see the results for myself :-)

old RTS: 0m54.296s
threaded RTS (-N1):    0m56.839s
threaded RTS (-N2):    0m52.623s

Wow!  3x the performance for a simple change.  Frustrating that there
isn't a protable/standard way to express this.  Also frustrating that
the threaded version doesn't improve on the situation (utilization is
back at 50%).

Anyway, that was a fun miro-benchmark to play with.


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