On Tue, Apr 20, 2004 at 01:59:33PM +0100, Simon Marlow wrote:
> On 20 April 2004 12:48, Bernard James POPE wrote:
>
> > Results:
> >
> > method runtime (s)
> > ---------------------------
> > pure 0.7
> > ffi 3.2
> > fastMut 15
> > ioref 23
>
> I very strongly suspect that it is the unsafePerformIO that hurts
> performance in the fastMut case. Otherwise this case would be around
> the same speed as the FFI example, perhaps faster.
>
> You could try out that theory by copying the definition of
> unsafePerformIO into your code, and putting an INLINE pragma on it. I
> think it's safe to do this in your case (it's not safe in general).
The time for fastMut with unsafePerformIO inlined is:
3.6 sec
The code is below. Note I dropped the NOINLINE pragmas on counter and inc.
This was necessary to get the fast time (is this safe?, it gives the right
answer here but ...). Also I removed the constant 100000000 from the code
(though it doesn't make any difference).
Thanks to all who have chipped in.
Cheers,
Bernie.
--------------------------------------------------------------------------------
{-# OPTIONS -fglasgow-exts #-}
module Main where
import GHC.IOBase hiding (unsafePerformIO)
import FastMutInt
import GHC.Base
counter :: FastMutInt
counter = unsafePerformIO newFastMutInt
inc :: Int -> ()
inc n = unsafePerformIO $
do incFastMutIntBy counter n
return ()
printCounter :: IO ()
printCounter
= do val <- readFastMutInt counter
print val
main :: IO ()
main = do line <- getLine
writeFastMutInt counter 0
seq (loop (read line)) printCounter
loop :: Int -> ()
loop 0 = ()
loop n = seq (inc n) (loop $! n - 1)
{-# INLINE unsafePerformIO #-}
unsafePerformIO :: IO a -> a
unsafePerformIO (IO m) = case m realWorld# of (# _, r #) -> r
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