Hi, I just updated to GHC 6.12.1, and I noticed a significant drop in I/O performance that I can't explain. The following code is a simple re-implementation of cat(1), i.e. it just echos all data from standard input to standard output:

module Main ( main ) where

import System.IO import Foreign ( allocaBytes )

bufsize :: Int bufsize = 4 * 1024

catBuf :: Handle -> Handle -> IO () catBuf hIn hOut = allocaBytes bufsize input where input ptr = hGetBuf hIn ptr bufsize >>= output ptr output _ 0 = return () output ptr n = hPutBuf hOut ptr n >> input ptr

main :: IO () main = do mapM_ (\h -> hSetBuffering h NoBuffering) [ stdin, stdout ] catBuf stdin stdout

That program used to have exactly the same performance as /bin/cat, but now it no longer does: | $ dd if=/dev/urandom of=test.data bs=1M count=512 | | $ time /bin/cat /dev/null | | real 0m1.939s | user 0m0.003s | sys 0m1.923s | | $ time ./cat-hgetbuf /dev/null | | real 0m4.327s | user 0m1.967s | sys 0m2.317s I've tested different variants of the program that were built with -O, -O2, and -O2 -funbox-strict-fields, respectively, but it doesn't seem to make a difference. Is there something I'm missing? Any suggestion would be kindly appreciated. Take care, Peter