First of all, thanks a lot for your quick answer!
However, the question is what are the approximate limits
of this super-linear speedup? I mean, is it acceptable, if
parallelization happens even 100 time faster?
How can I calculate the limits of this speedup via the
cache size of my processor?
Cheers,
Burak.
CC:
haskell-cafe@haskell.orgFrom:
ekirpichov@gmail.comSubject: Re: [Haskell-cafe] Parallel Karatsuba - A Weird speed up value greater than 4 on an Intel Quadcore CPU!
Date: Sat, 24 Dec 2011 19:53:26 +0400
To:
ekcburak@hotmail.com
Superlinear speedup can occur due to the increased cache size.
Dear List,
I am trying to parallelize Karatsuba multiplication with Haskell's
second generation strategies. Although, I am running the code on an
Intel quad-core CPU, I abnormally have a speedup much greater
than 4, around 10, which means a weird parallelization or something
occurs.
I would be appreciated, if anyone make some comments on the issue
explaining the possible reasons why this weird incident occurs?
Here is the basic parallel portion of the code:
karatsuba :: Int -> [Bool] -> [Bool] -> [Bool]
karatsuba _ [] _ = []
karatsuba _ _ [] = []
karatsuba currentDepth xs ys
| (l < 32 || currentDepth >= limit) = mul xs ys
| otherwise = (x `add` (replicate l False ++ (z `add` (replicate l False ++ y)))) `Main.using` strategy
where
l = (min (length xs) (length ys)) `div` 2
(xs0, xs1) = splitAt l xs
(ys0, ys1) = splitAt l ys
x = (normalize (karatsuba (currentDepth+1) xs0 ys0))
y = (normalize (karatsuba (currentDepth+1) xs1 ys1))
z = ((karatsuba (currentDepth+1) (add xs0 xs1) (add ys0 ys1)) `sub` (normalize (karatsuba (currentDepth+1) xs0 ys0)) `sub` (normalize (karatsuba (currentDepth+1) xs1 ys1)))
strategy res = do (Main.rpar) (x)
(Main.rpar) (y)
(Main.rpar) (z)
Main.rdeepseq res
Many thanks in advance and kind regards.
Saluti,
Burak.