[GHC] #11725: Performance Regression from 7.8.3 to 7.10.3

20 Mar 2016

      #11725: Performance Regression from 7.8.3 to 7.10.3
-------------------------------------+-------------------------------------
           Reporter:  dominic        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           Keywords:                 |  Operating System:  Linux
       Architecture:                 |   Type of failure:  Runtime
  Unknown/Multiple                   |  performance bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Some time ago I wrote a little test program for random number generation.
 Under 7.8.3 I get

 {{{
 Total   time    9.03s  (  9.15s elapsed)
 }}}

 Under 7.10.3 I get

 {{{
 Total   time   24.773s  ( 25.288s elapsed)
 }}}

 Now of course it could be the libraries that I am using rather than GHC
 itself so I have tried to make them as similar as possible. For 7.8.3 I
 have

 {{{
   build-depends:      base ==4.7.0.1,
                       mtl ==2.1.3.1,
                       primitive == 0.6,
                       mwc-random == 0.13.3.2,
                       vector == 0.10.12.3,
                       random ==1.1,
                       random-fu == 0.2.6.2,
                       random-source == 0.3.0.6
 }}}

 For 7.10.3 I have

 {{{
   build-depends:      base ==4.8.2.0,
                       mtl ==2.2,
                       primitive == 0.6,
                       mwc-random == 0.13.3.2,
                       vector == 0.10.12.3,
                       random ==1.1,
                       random-fu == 0.2.6.2,
                       random-source == 0.3.0.6
 }}}

 So the only differences are in mtl and base. I don’t seem to be able to
 coax cabal into using mtl-2.2 for 7.8.3 with all the other required
 libraries.

 {{{
 dominic@ghcPerformance:~$ cabal install 'random-source ==0.3.0.6' 'random-
 fu ==0.2.6.2' 'random ==1.1' 'primitive ==0.6' 'mwc-random ==0.13.3.2'
 'mtl ==2.2' 'vector ==0.10.12.3' --with-ghc=ghc-7.10.3
 Resolving dependencies...
 All the requested packages are already installed:
 mtl-2.2
 mwc-random-0.13.3.2
 primitive-0.6
 random-1.1
 random-fu-0.2.6.2
 random-source-0.3.0.6
 vector-0.10.12.3
 Use --reinstall if you want to reinstall anyway.
 dominic@ghcPerformance:~$ cabal install 'random-source ==0.3.0.6' 'random-
 fu ==0.2.6.2' 'random ==1.1' 'primitive ==0.6' 'mwc-random ==0.13.3.2'
 'mtl ==2.2' 'vector ==0.10.12.3' --with-ghc=ghc-7.8.3
 Resolving dependencies...
 cabal: Could not resolve dependencies:
 trying: random-source-0.3.0.6/installed-70e... (user goal)
 next goal: mtl (user goal)
 rejecting: mtl-2.2.1, 2.2.0.1 (global constraint requires ==2.2)
 rejecting: mtl-2.2/installed-cc5..., 2.2 (conflict: random-source =>
 mtl==2.1.3.1/installed-8bc...)
 rejecting: mtl-2.1.3.1/installed-8bc..., 2.1.3.1, 2.1.2, 2.1.1, 2.1,
 2.0.1.1,
 2.0.1.0, 2.0.0.0, 1.1.1.1, 1.1.1.0, 1.1.0.2, 1.1.0.1, 1.1.0.0, 1.0 (global
 constraint requires ==2.2)
 Backjump limit reached (change with --max-backjumps).
 }}}

 Cabal seems to be telling me that random-source-0.3.0.6 is the problem but
 if I look at the constraints for that package here
 https://hackage.haskell.org/package/random-source then I see

 {{{
  mtl (>=1 && <3)
 }}}

 I am not sure how to proceed from here. I’d like to solve this myself but
 I don’t want to start building versions of ghc to see which change caused
 the regression without first eliminating mtl.

 Any ideas would be gratefully received.

 {{{
 {-# LANGUAGE TemplateHaskell   #-}
 {-# LANGUAGE GADTs             #-}
 {-# LANGUAGE FlexibleInstances #-}

 import Data.Random
 import Data.Random.Source
 import qualified System.Random.MWC as MWC
 import Control.Monad.Reader
 import Control.Monad.Primitive

 $(monadRandom [d|
   instance (PrimMonad m, s ~ PrimState m) => MonadRandom (ReaderT (MWC.Gen
 s) m) where
     getRandomWord16 = ask >>= lift . MWC.uniform
     getRandomWord32 = ask >>= lift . MWC.uniform
     getRandomWord64 = ask >>= lift . MWC.uniform
   |])

 testUniform :: MonadRandom m => Int -> m [Double]
 testUniform n = replicateM (fromIntegral n) (sample stdUniform)

 n :: Int
 n = 10^7

 main :: IO ()
 main = do
     seed <- MWC.create
     xs <- runReaderT (testUniform n) seed
     print (sum xs / fromIntegral n)
 }}}

 This cabal file will build this on 7.8.3

 {{{
 name:                PerfTest8
 version:             0.1.0.0
 homepage:            TBD
 license:             MIT
 author:              Dominic Steinitz
 maintainer:          idontgetoutmuch@gmail.com
 category:            System
 build-type:          Simple
 cabal-version:       >=1.10

 executable Random8
   main-is:            TestMwcViaRandomSource.hs
   build-depends:      base ==4.7.0.1,
                       mtl ==2.1.3.1,
                       primitive == 0.6,
                       mwc-random == 0.13.3.2,
                       vector == 0.10.12.3,
                       random ==1.1,
                       random-fu == 0.2.6.2,
                       random-source == 0.3.0.6
   default-language:   Haskell2010
 }}}

 This cabal file will build this on 7.10.3

 {{{
 name:                PerfTest10
 version:             0.1.0.0
 homepage:            TBD
 license:             MIT
 author:              Dominic Steinitz
 maintainer:          idontgetoutmuch@gmail.com
 category:            System
 build-type:          Simple
 cabal-version:       >=1.10

 executable Random10
   main-is:            TestMwcViaRandomSource.hs
   build-depends:      base ==4.8.2.0,
                       mtl ==2.2,
                       primitive == 0.6,
                       mwc-random == 0.13.3.2,
                       vector == 0.10.12.3,
                       random ==1.1,
                       random-fu == 0.2.6.2,
                       random-source == 0.3.0.6
   default-language:   Haskell2010
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11725
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