dropAlphaLayer - big allocations rate

[Alex Sharov]

Input: 1200x12000 image
Produce 1 Billion allocations

Benchmark code:

module Main where

import           Codec.Picture
import           Codec.Picture.Types
import           Control.Exception
import           Criterion
import           Criterion.Main      (defaultMain)
import           Weigh

main :: IO ()
main = do
  f1 <- readPng "test-png-original.png"
  let img = toRgba8 $ unpack f1

  -- bench time
  defaultMain
    [ bgroup
        "lib"
        [ bench "dropAlphaLayer" $ whnf dropAlphaLayer img
        ]
    ]

  -- bench memory
  mainWith (wgroup "lib" (do
      func "dropAlphaLayer" dropAlphaLayer img
    ))

unpack :: Either String DynamicImage -> DynamicImage
unpack eitherImg =
  case eitherImg of
    Left e         -> throw (WrongFile e)
    Right original -> original

toRgba8 :: DynamicImage -> Image PixelRGBA8
toRgba8 dynImage =
  case dynImage of
    ImageRGBA8 img  -> img
    _ -> undefined

Results:

  Case              Allocated  GCs
  dropAlphaLayer  960,478,912  918

[Alex Sharov]

Hmm... Looks like "allocations" in Haskell world has another meaning (it including heap and stack allocations). Will close ticket and try more profiling techniques from http://book.realworldhaskell.org/read/profiling-and-optimization.html