Re: [Haskell-cafe] Ridiculously slow FFI, or cairo binding?

+gtk2hs-users On Wed, Nov 2, 2011 at 2:10 PM, Eugene Kirpichov wrote:

Oh. This is pretty crazy, I wonder what they're doing with GMP so much...

I modified the Haskell program to use cairo directly, even with safe calls, and it now takes the same time as the C program.

{-# LANGUAGE ForeignFunctionInterface #-} module Main where

import qualified Graphics.Rendering.Cairo as C import Control.Monad import Foreign import Foreign.C.Types import Foreign.C.String

foreign import ccall "cairo.h cairo_image_surface_create" cairo_image_surface_create :: CInt -> CInt -> CInt -> IO (Ptr ()) foreign import ccall "cairo.h cairo_create" cairo_create :: Ptr () -> IO (Ptr ()) foreign import ccall "cairo.h cairo_set_source_rgb" cairo_set_source_rgb :: Ptr () -> CDouble -> CDouble -> CDouble -> IO () foreign import ccall "cairo.h cairo_rectangle" cairo_rectangle :: Ptr () -> CDouble -> CDouble -> CDouble -> CDouble -> IO () foreign import ccall "cairo.h cairo_fill" cairo_fill :: Ptr () -> IO () foreign import ccall "cairo.h cairo_surface_write_to_png" cairo_surface_write_to_png :: Ptr () -> CString -> IO ()

main = do s <- cairo_image_surface_create 0 1024 768 cr <- cairo_create s cairo_set_source_rgb cr 0 255 0 forM_ [0,2..1024] $ \x -> do forM_ [0,2..768] $ \y -> do cairo_rectangle cr x y 1 1 cairo_fill cr pic <- newCString "picture.png" cairo_surface_write_to_png s pic

On Wed, Nov 2, 2011 at 1:58 PM, Vincent Hanquez wrote:

...

On 11/02/2011 09:51 AM, Eugene Kirpichov wrote:

...

Hi Claude,

I suspected that the issue could be about unsafe foreign imports - all imports in the cairo bindings are "safe". I compiled myself a version of cairo bindings with the "rectangle" and "fill" functions marked as unsafe.

Unfortunately that didn't help the case at all, even though the core changed FFI calls from "__pkg_ccall_GC" to "__pkg_ccall". The performance stayed the same; the overhead is elsewhere.

doing a ltrace, i think the reason is pretty obvious, there's a lot of GMP calls:

__gmpz_init(0x7f5043171730, 1, 0x7f5043171750, 0x7f5043171740, 0x7f50431d2508) = 0x7f50431d2530 __gmpz_mul(0x7f5043171730, 0x7f5043171750, 0x7f5043171740, 0x7f50431d2538, 0x7f50431d2508) = 1 __gmpz_init(0x7f5043171728, 1, 0x7f5043171748, 0x7f5043171738, 0x7f50431d2538) = 0x7f50431d2568 __gmpz_mul(0x7f5043171728, 0x7f5043171748, 0x7f5043171738, 0x7f50431d2570, 0x7f50431d2538) = 1 __gmpn_gcd_1(0x7f50431d2580, 1, 1, 1, 1) = 1 <repeated thousand of time>

before each call cairo calls.

just to make sure, the C version doesn't exhibit this behavior.

-- Vincent

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-- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/

-- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/