Thank you Simon, I will obtain parallel 2.2.0.1 and work with it.
Actually, the reason I asked my question was because I did not
think forceParList should yield better performance than parList
(unless it was becasue of the foldl?).
I read the release notes for 6.12.1 about the work done on the ghc
parallel framework and did just a little bit more experimenting.
You might find this of interesting.
ghc 6.10.4 with parallel 1.1.0.1 (as reported before):
Serial algorithm: 1.00 unit of time
Parallel algorithm with parList: 0.81 units of time
Parallel algorithm with forceParList: 0.58 units of time
ghc 6.12.1 with parallel 1.1.0.1:
Serial algorithm: 1.00 unit of time
Parallel algorithm with parList: 0.58 units of time*
Parallel algorithm with forceParList: 0.58 units of time*
Interesting. Well, from my perspective, 6.12.1 is certainly an
improvement here.
Cheers,
- Marcus
Simon Marlow wrote:
>
> On 18/12/2009 18:31, Marcus D. Gabriel wrote:
>> Hello,
>>
>> In Control.Parallel.Strategies, parList is defined as
>>
>> parList strat [] = ()
>> parList strat (x:xs) = strat x `par` (parList strat xs)
>>
>> with
>>
>> parMap strat f xs = map f xs `using` parList strat.
>>
>> I have recently found that if I define
>>
>> forceParMap strat f xs = map f xs `using` forceParList strat
>>
>> where
>>
>> forceParList strat = foldl (\done -> (done>||) . strat) ()
>>
>> then to date, forceParList via forceParMap gives faster results
>> than parList via parMap. For example, in one experiment, parMap
>> with parList run at 0.81 the time of the serial solution whereas
>> forceParMap with forceParList run at 0.58 the time of the serial
>> solution. This is to say, forceParList completed in 0.72 the
>> time of parList. So,
>>
>> 1. Why is forceParList faster than parList?
>> 2. Is this generic to the ghc runtime model or a particularity
>> of the ghc implementation?
>
> I'm not sure. Your forceParList looks equivalent to parList, unless
> I'm misreading it.
>
> I recommend trying out the new parallel package, here:
>
> http://hackage.haskell.org/package/parallel
>
> which has a new implementation of Strategies. The version of parList
> you quoted above has a space leak problem which may be affecting your
> results.
>
> Cheers,
> Simon
_______________________________________________
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
