Hello All
I am trying to understand the Strategies ( http://hackage.haskell.org/packages/archive/parallel/3.2.0.2/doc/html/Control-Parallel-Strategies.html ) and wrote this quick code.
import Data.List
import Control.Parallel.Strategies
fun :: [ Int ] -> [ Int ]
fun [] = []
fun ( x : xs ) = ( x + 1 ) : fun xs
main = do
let xs = ( fun [ 1..1000000 ] ) `using` parListChunk 500000 rdeepseq
return ()
When I am running this code due to laziness , the xs is not evaluating.
[mukesh.tiwari@user ParallelStrat]$ time ./Main +RTS N1 s
48,320 bytes allocated in the heap
5,928 bytes copied during GC
38,592 bytes maximum residency (1 sample(s))
14,656 bytes maximum slop
1 MB total memory in use (0 MB lost due to fragmentation)
Tot time (elapsed) Avg pause Max pause
Gen 0 0 colls, 0 par 0.00s 0.00s 0.0000s 0.0000s
Gen 1 1 colls, 0 par 0.00s 0.00s 0.0002s 0.0002s
Parallel GC work balance: nan (0 / 0, ideal 1)
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)
SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)
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)
Alloc rate 48,368,368 bytes per MUT second
Productivity 0.0% of total user, 0.0% of total elapsed
gc_alloc_block_sync: 0
whitehole_spin: 0
gen[0].sync: 0
gen[1].sync: 0
real 0m0.003s
user 0m0.002s
sys 0m0.001s
[mukesh.tiwari@user ParallelStrat]$ time ./Main +RTS N2 s
48,248 bytes allocated in the heap
40 bytes copied during GC
38,440 bytes maximum residency (1 sample(s))
18,904 bytes maximum slop
2 MB total memory in use (0 MB lost due to fragmentation)
Tot time (elapsed) Avg pause Max pause
Gen 0 0 colls, 0 par 0.00s 0.00s 0.0000s 0.0000s
Gen 1 1 colls, 0 par 0.00s 0.00s 0.0001s 0.0001s
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 (bound) : 0.00s ( 0.00s) 0.00s ( 0.00s)
Task 2 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s)
SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)
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)
Alloc rate 48,248,000,000,000 bytes per MUT second
Productivity 100.0% of total user, 0.0% of total elapsed
gc_alloc_block_sync: 0
whitehole_spin: 0
gen[0].sync: 0
gen[1].sync: 0
real 0m0.004s
user 0m0.000s
sys 0m0.004s
The library doc suggest that parListChunk divides a list into chunks, and applies the strategy evalList strat to each chunk in parallel. Looking at the source code ( http://hackage.haskell.org/packages/archive/parallel/3.2.0.2/doc/html/src/Control-Parallel-Strategies.html#parListChunk ) , list is split into chunks and then strategy is applied parallel to every chunk. Could some one please tell me what is wrong with this concept and why the code above is showing laziness.
Regards
Mukesh Tiwari