[Haskell-cafe] Performance of concurrent array access

Andreas Voellmy andreas.voellmy at gmail.com
Tue Aug 23 23:07:54 CEST 2011

Thanks for the suggestions. I tried to add strictness in the following

(1) Changing "insertDAT a j c" to "insertDAT a j $! c"
(2) Changing "insertDAT a j c" to "deepseq c (insertDAT a j c)"

I also used Int instead of Int32 throughout and changed the DAT data type to
a newtype definition. These changes improved the performance slightly, but
still, the multithreaded runs perform significantly worse than the
single-threaded runs, by about the same amount (i.e. 0.5 seconds more for
the 2 core run than for the 1 core run).

I used ghc 7.0.3 for the performance measurements I gave in my message. I've
also tried under 7.2.1, and I get basically the same behavior there.


On Tue, Aug 23, 2011 at 4:38 PM, Johan Tibell <johan.tibell at gmail.com>wrote:

> On Tue, Aug 23, 2011 at 10:04 PM, Andreas Voellmy
> <andreas.voellmy at gmail.com> wrote:
> > data DAT = DAT (IOArray Int32 Char)
> Try to make this a newtype instead. The data type adds a level of
> indirection.
> >   do let p j c = insertDAT a j c >> lookupDAT a j >>= \v -> v `pseq`
> return
> > ()
> You most likely want (insertDAT a j $! c) to make sure that the
> element is force, to avoid thunks building up in the array.
> > -- Parameters
> > arraySize :: Int32
> Int might work better than Int32. While they should behave the same on
> 32-bit machines Int might have a few more rewrite rules that makes it
> optimize better.
> -- Johan
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