#3586: Initialisation of unboxed arrays is too slow
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Reporter: simonpj | Owner:
Type: run-time performance bug | Status: new
Priority: high | Milestone: 6.12.2
Component: libraries (other) | Version: 6.10.4
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Os: Unknown/Multiple
Architecture: Unknown/Multiple |
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Comment (by dons):
Hello Philippos, you should take up these general design questions on the
[email protected] mailing list, not on the bug tracker.
Some quick points: since you use the mersenne-twister in Clean, you should
use it in Haskell too: http://hackage.haskell.org/package/mersenne-random.
Also, you should never need to increase the stack size with the -K option.
Finally, it is faster to thread around a seed to the random generator,
than to generate the infinite list of randoms.
Here's how I would translate your Clean program to Haskell:
{{{
{-# LANGUAGE BangPatterns #-}
{-# OPTIONS -funbox-strict-fields #-}
--
-- Compile with: ghc -O2 -fvia-C -optc-O3 --make A.hs
-- Run with : ./A +RTS -H200M
--
-- $ time ./A +RTS -H200M
-- 2.77000034e8
-- ./A +RTS -H200M 0.62s user 0.10s system 96% cpu 0.751 total
--
import Control.Monad.ST
import Control.Monad
import Data.Array.ST
import Data.Array.Base
import System.Random.Mersenne
data Op = And | Or | Not
data Tree = L !Double | T !Op [Tree]
main = do
g <- getStdGen
print $ runST $ do
let l = 0
u = 2000000 - 1
vt <- unsafeNewArray_ (l,u)
forM_ [l..u] $ \i -> unsafeWrite vt i (L 137)
fn u vt 0 g
fn :: Int -> STArray s Int Tree -> Double -> MTGen -> ST s Double
fn i a !acc g | i < 1 = return acc
fn i a acc g = do
i1 <- ri `fmap` unsafeIOToST (random g) :: ST s Int
i2 <- ri `fmap` unsafeIOToST (random g) :: ST s Int
b <- a `readArray` i1
writeArray a i2 (set (get b + 3))
c <- a `readArray` i1
fn (i-1) a (get c + acc) g
ri :: Int -> Int
ri x = (abs x) `rem` 2000000
get :: Tree -> Double
get (L r) = r
get _ = 0.0
set :: Double -> Tree
set r = L r
}}}
Your Haskell version completes for me in just over 2 minutes. The above
Haskell version completes in 0.7s. I'd imagine this is very competitive
with the Clean implementation? I give detailed instructions on how to
compile this for best results.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3586#comment:15>
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