mukesh tiwari mukeshtiwari.iiitm at gmail.com
Sat Dec 10 19:14:47 CET 2011

```Hello all
I am trying to learn parallel Haskell and  I have gone through couple of
resources ( Real world Haskell and
http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel/AFP08-notes.pdf
).
I understood par and pseq and I wrote matrix multiplication using these two
function but it does not look.  Although I did not get all these details
but none of the sparks converted which is really important for parallel
programming. Could some one please tell me how to improve this. Also kindly
recommend me some  literature for parallel programming in Haskell.

Regards
Mukesh Tiwari

import Data.List
import Control.Parallel

parHelp :: ( Num a ) => [ a ] -> [ a ] -> a
parHelp [] [] = 0
parHelp ( x : xs ) ( y : ys ) = ret where
ret = par a ( pseq a ( a + parHelp xs ys ) ) where
a = x * y

helpMult :: ( Num a ) => [ a ] -> [ [ a ] ] -> [ a ]
helpMult _ [] = []
helpMult x ( y : ys ) = ret where
ret =  par a ( pseq a  ( a : helpMult x ys ) ) where
a = parHelp x y

mult :: ( Num a ) => [ [ a ] ] -> [ [ a ] ] -> [ [ a ] ]
mult [] _ = []
mult ( x : xs ) ys = ret where
ret = par a ( pseq a  ( a : mult xs ys ) ) where
a = helpMult x ys

main = print \$ mult [[1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4] ] (
transpose [[1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4] ])

[1 of 1] Compiling Main             ( Matpar.hs, Matpar.o )
[user at haskell Programming]\$ ./Matpar +RTS -N2 -s
./Matpar +RTS -N2 -s
[[10,20,30,40],[10,20,30,40],[10,20,30,40],[10,20,30,40]]
85,480 bytes allocated in the heap
5,216 bytes copied during GC
47,328 bytes maximum residency (1 sample(s))
22,304 bytes maximum slop
2 MB total memory in use (0 MB lost due to fragmentation)

Generation 0:     0 collections,     0 parallel,  0.00s,  0.00s elapsed
Generation 1:     1 collections,     0 parallel,  0.00s,  0.00s elapsed

Parallel GC work balance: -nan (0 / 0, ideal 2)

MUT time (elapsed)       GC time  (elapsed)
Task  0 (worker) :    0.00s    (  0.00s)       0.00s    (  0.00s)
Task  1 (worker) :    0.00s    (  0.00s)       0.00s    (  0.00s)
Task  2 (bound)  :    0.00s    (  0.00s)       0.00s    (  0.00s)
Task  3 (worker) :    0.00s    (  0.00s)       0.00s    (  0.00s)

*  SPARKS: 84 (0 converted, 0 pruned)*

INIT  time    0.00s  (  0.00s elapsed)
MUT   time    0.00s  (  0.00s elapsed)
GC    time    0.00s  (  0.00s elapsed)
EXIT  time    0.00s  (  0.00s elapsed)
Total time    0.00s  (  0.00s elapsed)

%GC time      33.3%  (13.5% elapsed)

Alloc rate    42,761,380 bytes per MUT second

Productivity  33.3% of total user, 45.0% of total elapsed

gc_alloc_block_sync: 0
whitehole_spin: 0
gen.sync_large_objects: 0
gen.sync_large_objects: 0