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

[Eugene Kirpichov]

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 <tab at snarc.org> 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/
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