That sounds bad. What happens with 8.0? Big CAFs like [1..40000000] can be problematic... does it happen in the more realistic situation where the bounds are data dependent? Open a ticket? Simon | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Facundo | DomÃnguez | Sent: 06 January 2016 18:40 | To: ghc-devs@haskell.org | Subject: Slowdown in concurrent program | | Dear devs, | The following program shows worse measures when compiled with -O | with both ghc-7.10.2 and ghc-7.8.3. | | Am I hitting a known bug? Or may someone point a mistake in the code? | | It also shows worse measures when using anything other than -N1. | | Thanks in advance, | Facundo | | -- /opt/ghc-7.8.3/bin/ghc --make -threaded -fforce-recomp test.hs | -- time ./test: 10 seconds | -- | -- /opt/ghc-7.8.3/bin/ghc --make -threaded -O -fforce-recomp test.hs | -- time ./test: 48 seconds | -- | -- /opt/ghc-7.10.2/bin/ghc --make -threaded -fforce-recomp test.hs | -- time ./test: 23 seconds | -- | -- /opt/ghc-7.10.2/bin/ghc --make -threaded -O -fforce-recomp test.hs | -- time ./test: 57 seconds | -- | | import Control.Concurrent | import Control.Monad | import Data.List | | | main :: IO () | main = do | let xs = [ 1 .. 400000000] | mv <- newEmptyMVar | replicateM_ 4 $ forkIO $ putMVar mv $! foldl' (+) 0 xs | nums <- replicateM 4 $ takeMVar mv | print (nums :: [Integer]) | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail.haskell. | org%2fcgi-bin%2fmailman%2flistinfo%2fghc- | devs&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7cc87535716ced49a12e3308 | d316c8c028%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=4W%2b0W36E1O%2bZtxzEX | Besrv%2fUk6fwsvNGc5RqUAwMHDk%3d