#4184: Squirrelly inliner behaviour leads to 80x slowdown
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Reporter: bos | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.12.1 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
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Recently, I switched the mwc-random package
(http://hackage.haskell.org/package/mwc-random) over from running in the
ST monad to using Roman's primitive package. I didn't notice initially,
but this caused a huge performance regression.
mwc-random 0.4.1.1 uses ST internally, and runs the benchmarks/Quickie
benchmark in 0.017 seconds.
mwc-random 0.5.1.3 uses PrimMonad internally, and takes 1.328 seconds to
run the same benchmark.
That's about a factor of 80 slowdown. This causes a massive knock-on
performance loss in packages such as criterion that need fast PRNGs.
The problem is very easy to reproduce:
cabal install mwc-random-0.4.1.1
cabal install mwc-random-0.5.1.3
darcs get http://darcs.serpentine.com/mwc-random/
cd mwc-random/benchmarks
ghc -fforce-recomp -O -package mwc-random-0.4.1.1 --make Quickie -o
quickie-411
ghc -fforce-recomp -O -package mwc-random-0.5.1.3 --make Quickie -o
quickie-513
time ./quickie-411
time ./quickie-513
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4184>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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