我一直在使用该Repa
库开发路径跟踪器。我最近通过使用 monadic 重构了它以合并并行性computeP
。但是,我发现性能提升可以忽略不计。而且,监控htop
,似乎程序仍然只使用一个CPU。为了深入研究这个问题,我打开ghci
并运行了以下命令:
~
❯ stack ghci --package repa
Configuring GHCi with the following packages:
GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /tmp/ghci12667/ghci-script
Prelude> import Data.Array.Repa
Prelude Data.Array.Repa> import System.Random
Prelude Data.Array.Repa System.Random> randomList = randoms (mkStdGen 0)
Prelude Data.Array.Repa System.Random> shape = (Z :. 1000000)
Prelude Data.Array.Repa System.Random> array = fromFunction shape $ \(Z :. i) -> randomList !! i
Prelude Data.Array.Repa System.Random> sumP array
没有骰子。repa
似乎仍然只使用一个 CPU 内核,如下所示htop
:
sumP
此外,执行团队在和之间几乎没有变化sumS
,略偏向于sumS
:
Prelude Data.Array.Repa System.Random> array = fromListUnboxed (Z :. 1000000) $ take 1000000 $ randoms (mkStdGen 0)
(0.01 secs, 0 bytes)
Prelude Data.Array.Repa System.Random> sumP array
AUnboxed Z [500140.92257232184]
(0.99 secs, 1,916,158,952 bytes)
Prelude Data.Array.Repa System.Random> sumS array
AUnboxed Z [500140.92257232184]
(0.93 secs, 2,348,156,248 bytes)
我错过了什么?万一这很重要,我使用的是 Arch Linux:
~
❯ uname -a
Linux roskolnikov 4.11.9-1-ARCH #1 SMP PREEMPT Wed Jul 5 18:23:08 CEST 2017 x86_64 GNU/Linux
更新
一些评论表明我应该使用文档中指示的-threaded
选项。我处于默认使用的(错误?)印象之下。无论如何,我的程序已经在使用这些标志——这是文件中的片段:ghci
repa
ghci
-threaded
.cabal
executable write
hs-source-dirs: app
main-is: Write.hs
ghc-options: -Odph
-rtsopts
-threaded
-fno-liberate-case
-funfolding-use-threshold1000
-funfolding-keeness-factor1000
-fllvm
-optlo-O3
build-depends: base
, pathtracer
, repa
, JuicyPixels
default-language: Haskell2010
此外,我在ghci
使用(我认为)正确的 ghci 选项时重新运行了命令:
~
❯ stack ghci\
--package repa\
--ghc-options -Odph\
--ghc-options -rtsopts\
--ghc-options -with-rtsopts=-N\
--ghc-options -threaded\
--ghc-options -fno-liberate-case\
--ghc-options -funfolding-use-threshold1000\
--ghc-options -funfolding-keeness-factor1000\
--ghc-options -fllvm\
--ghc-options -optlo-O3
Configuring GHCi with the following packages:
when making flags consistent: warning:
-O conflicts with --interactive; -O ignored.
GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /tmp/ghci31252/ghci-script
Prelude> import Data.Array.Repa
Prelude Data.Array.Repa> import System.Random
Prelude Data.Array.Repa System.Random> randomList = randoms (mkStdGen 0)
Prelude Data.Array.Repa System.Random> shape = (Z :. 1000000)
Prelude Data.Array.Repa System.Random> array = fromFunction shape $ \(Z :. i) -> randomList !! i
Prelude Data.Array.Repa System.Random> sumP array
仍然没有骰子:
对于此事,我深表感谢任何进一步的帮助。