Apologies, didn't see the link on my phone :)
As the comment on the link shows, youre accidentally migrating unevaluated work to the main thread, hence no speedup.
Be very careful with evaluation strategies (esp. lazy expressions) around MVar and TVar points. Its too easy to put a thunk in one.
The strict-concurrency package is one attempt to invert the conventional lazy box, to better match thge most common case.
What do you exactly mean? I have included link to full source listing:
http://hpaste.org/83460.
--
Łukasz Dąbek
2013/3/4 Don Stewart <dons00@gmail.com>:
> Depends on your code...
>
> On Mar 4, 2013 6:10 PM, "Łukasz Dąbek" <sznurek@gmail.com> wrote:
>>
>> Hello Cafe!
>>
>> I have a problem with following code: http://hpaste.org/83460. It is a
>> simple Monte Carlo integration. The problem is that when I run my
>> program with +RTS -N1 I get:
>> Multi
>> 693204.039020917 8.620632s
>> Single
>> 693204.039020917 8.574839s
>> End
>>
>> And with +RTS -N4 (I have four CPU cores):
>> Multi
>> 693204.0390209169 11.877143s
>> Single
>> 693204.039020917 11.399888s
>> End
>>
>> I have two questions:
>> 1) Why performance decreases when I add more cores for my program?
>> 2) Why performance of single threaded integration also changes with
>> number of cores?
>>
>> Thanks for all answers,
>> Łukasz Dąbek.
>>
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