I have included a new and improved version.
Just to make the comparison a little more reasonable I re-wrote the
program using ML and ran it with SMLNJ
eal 0m3.175s
user 0m0.935s
sys 0m0.319s
Here's the compiled haskell (ghc -O2 foo.hs -o foo):
real 0m16.855s
user 0m9.724s
sys 0m0.495s
OUCH.
I verified to make sure they were both writing valid data files.
I'm trying to learn how to fish, so I'm truly interested in finding
out _how_ to optimize using profiling and other such tools.
Here's the header of the foo.prof file:
total time = 9.44 secs (472 ticks @ 20 ms)
total alloc = 2,171,923,916 bytes (excludes profiling overheads)
2GB of allocation ??? with a base size of 131k. that seems excessive,
which gets me back to the , I don't
think I'm interpreting profiling stuff correctly.
This line is a little more interesting:
COST CENTRE
MODULE no. entries
%time %alloc %time %alloc
main
Main 178 1
98.7 99.1 98.7 99.1
So even though getData should be doing all of the allocation, main's
using a lot of time and effort. I figured it
was the show's that were slowing things up (how do I get profiling to
show that detail ?), so I had it output just "\n".
Well that finishes in no time at all.
And yea, verily, the output of the .prof file.
total time = 0.14 secs (7 ticks @ 20 ms)
total alloc = 65,562,824 bytes (excludes profiling overheads)
So I guess it's the show's, but I can't seem to find more efficient
float output.
FFI to sprintf ? yuch.
Brian
foo.hs
import Numeric
import Complex
import IO
genData :: Double -> Int -> (Double -> Complex Double) -> ([Double],
[Complex Double])
genData tstop n f =
let deltat = tstop / (fromIntegral n)
t = [ fromIntegral(i) * deltat | i <- [0..n-1]]
in
(t, map f t)
main =
do let (t, y) = genData 100.0E-6 (2 ^ 17) (\x -> x :+ 0.0)
h <- openFile "/dev/null" WriteMode
mapM_ (\(x, y) ->
do hPutStr h ((showEFloat (Just 6) x) " ")
hPutStr h (showEFloat (Just 6) (realPart y)
"\n"))
(zip t y)
hClose h
print "Done"
foo.sml
let fun genData tstop n f =
let val deltat = tstop / (Real.fromInt n)
val t = List.tabulate(n, fn i => Real.fromInt(i) * deltat)
in
(t, map f t)
end
val (t, y) = genData 100.0E~6 131072 (fn x => (x, 0.0))
val h = TextIO.openOut("data.txt")
in
List.app
(fn (x, (a,b)) =>
(TextIO.output(h, Real.fmt (StringCvt.SCI(SOME 6)) x);
TextIO.output(h, Real.fmt (StringCvt.SCI(SOME 6)) a ^
"\n")))
(ListPair.zip (t, y));
TextIO.closeOut(h);
print "Done";
()
end
On Jun 15, 2009, at 12:15 AM, Thomas ten Cate wrote:
How much output does this generate? Does it matter if you send the
output to /dev/null? This looks as if the bottleneck might well be in
I/O operations, not in the code itself. To find this out, you could
rewrite the code in C and see if that makes a difference?
Thomas
On Sun, Jun 14, 2009 at 20:44, brian<[email protected]> wrote:
Haskell Gurus,
I have tried to use profiling to tell me what's going on here, but
it hasn't
helped much, probably because I'm not interpreting the results
correctly.
Empirically I have determined that the show's are pretty slow, so an
alternative to them would be helpful. I replaced the show's with
"", and
compiled with -O2 and not much improvement.
I need to write _a lot_ of code in this style. A few words about
how best
to do this would be helpful. Laziness, infinite lists, uvector ??
Help...
Thanks,
Brian
import Complex
import System.IO
genData :: Double -> Int -> (Double -> Complex Double) -> ([Double],
[Complex Double])
genData tstop n f =
let deltat = tstop / (fromIntegral n)
t = [ fromIntegral(i) * deltat | i <- [0..n-1]]
in
(t, map f t)
main =
do let (t, y) = genData 100.0E-6 (2 ^ 15) (\x -> x :+ 0.0)
h <- openFile "data.txt" WriteMode
mapM_ (\(x, y) ->
do hPutStr h (show t)
hPutStr h " "
hPutStrLn h (show (realPart y)))
(zip t y)
hClose h
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