I've found DiffArrays to be way too slow/memory-hogging for real usage.
Since you are in IO already (StateT s IO), you'll probably be better
off using a mutable array for a data structure.
Some things are still best done in the imperative style. You can be a
bit safer by using ST as the bottom monad, however, and returning the
result as a pure array. This gives you a single copy per "runST".
Alternatively, use IntMap instead of arrays if you want a pure data
structure with reasonably efficient update/lookup.
-- ryan
On Tue, Mar 3, 2009 at 4:44 PM, Tobias Olausson
Hello all. I am currently implementing an emulation of a CPU, in which the CPU's RAM is part of the internal state that is passed around in the program using a state monad. However, the program performs unexpectingly bad, and some profiling information makes us believe that the problem is the high memory usage of the program.
The program below is similar to our main program used when testing a sorting algorithm in this CPU:
module Main where
import Control.Monad.State.Lazy import Data.Word import Data.Array.Diff import Control.Concurrent (threadDelay)
data LoopState = LoopState { intVal :: Integer , diff :: DiffUArray Word8 Word8 }
initState :: LoopState initState = LoopState 0 (array (0x00,0xFF) [(idx,0)|idx<-[0x00..0xFF]])
main :: IO () main = do execStateT looper initState >>= putStrLn . show . intVal
looper :: StateT LoopState IO () looper = do st <- get let res = intVal st + 1 idx = fromIntegral res put $ st { intVal = res, diff = (diff st) // [(idx,idx)] } if res == 13000000 then return () else looper
Of course our program does more than updating a counter ;-) Compiling and running this program yields the following result:
[~]:[olaussot] >> ghc --make -O2 -o array ArrayPlay.hs [~]:[olaussot] >> ./array +RTS -sstderr ./array +RTS -sstderr 13000000 313,219,740 bytes allocated in the heap 1,009,986,984 bytes copied during GC 200,014,828 bytes maximum residency (8 sample(s)) 4,946,648 bytes maximum slop 393 MB total memory in use (3 MB lost due to fragmentation)
Generation 0: 590 collections, 0 parallel, 3.06s, 3.09s elapsed Generation 1: 8 collections, 0 parallel, 3.56s, 4.21s elapsed
INIT time 0.00s ( 0.00s elapsed) MUT time 0.27s ( 0.27s elapsed) GC time 6.62s ( 7.30s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 6.89s ( 7.57s elapsed)
%GC time 96.1% (96.4% elapsed)
Alloc rate 1,155,958,754 bytes per MUT second
Productivity 3.9% of total user, 3.6% of total elapsed
Why does the program spend 96.1% of its total running time collecting garbage? Any tips to make this program perform better are appreciated. Please do tell if anything is unclear.
-- Tobias Olausson tobsan@gmail.com _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe