[Haskell-cafe] I/O performance drop in ghc 6.12.1
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 test.data /dev/null | | real0m1.939s | user0m0.003s | sys 0m1.923s | | $ time ./cat-hgetbuf test.data /dev/null | | real0m4.327s | user0m1.967s | 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I/O performance drop in ghc 6.12.1
On Jan 14, 2010, at 17:30 , Peter Simons wrote: 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: GHC 6.12.1 has the first release of UTF-8 support, so there's translation overhead. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I/O performance drop in ghc 6.12.1
On Thu, Jan 14, 2010 at 2:30 PM, Peter Simons sim...@cryp.to wrote: I just updated to GHC 6.12.1, and I noticed a significant drop in I/O performance that I can't explain. This is probably brought about by the new Unicode I/O support in 6.12. Your file isn't open in binary mode, so it's probably getting translated from something like UTF-8 before it reaches you. Might want to compare the two. I'm a little surprised by the magnitude of the difference; I might have expected it to be 33%, not 400%. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I/O performance drop in ghc 6.12.1
On Thu, Jan 14, 2010 at 11:38 PM, Bryan O'Sullivan b...@serpentine.com wrote: On Thu, Jan 14, 2010 at 2:30 PM, Peter Simons sim...@cryp.to wrote: I just updated to GHC 6.12.1, and I noticed a significant drop in I/O performance that I can't explain. This is probably brought about by the new Unicode I/O support in 6.12. Your file isn't open in binary mode, so it's probably getting translated from something like UTF-8 before it reaches you. Might want to compare the two. I'm a little surprised by the magnitude of the difference; I might have expected it to be 33%, not 400%. Hold on, he's using hGetBuf/hPutBuf. Although I'd suggest wrapping that in bytestrings.. the point is, those functions are documented to ignore encoding and always use binary I/O. There shouldn't be a difference at all. I wonder if the difference goes away if the handle is explicitly set to binary? It shouldn't, but then again it shouldn't exist in the first place. -- Svein Ove Aas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
