[Haskell-cafe] Threading and Mullticore Computation

[Andrew Coppin]

Bulat Ziganshin wrote:
> Hello Andrew,
>
> Tuesday, March 3, 2009, 9:21:42 PM, you wrote:
>
>   
>> I just tried it with GHC 6.10.1. Two capabilities is still slower. (See
>> attachments. Compiled with -O2 -threaded.)
>>     
>
> i don't think so:
>
>   Total time    4.88s  (  5.14s elapsed)
>
>   Total time    7.08s  (  4.69s elapsed)
>   

Damnit. Foiled again!

It turns out Process Explorer is reporting CPU time, not wall time. 
Sorry about that...

(This is the second time I've tripped over that one. There doesn't seem 
to be a way to get it to report wall time either, unfortunately.)

> so with 1 thread wall clock time is 5 seconds, with 2 thread wall time
> is 4.7 seconds
>   

So a small speedup then.

> so, my conclusion - this benchmark limited by memory latencies so it
> cannot be efficiently multithreaded
>   

Probably.