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