[Haskell-cafe] Haskell performance question

[Xiao-Yong Jin]

Don Stewart <dons at galois.com> writes:

> xj2106:
>> I used `unsafePerformIO' with `INLINE', because I don't know
>> where `inlinePerformIO' is now.  And also the `-optc-march'
>> is changed to `nocona'.
>
> Using unsafePerformIO here would break some crucial inlining.
> (the same trick is used in Data.ByteString, by the way).
>
> You can find inlinePerformIO is in Data.ByteString.Internal.
>
> Comparing the two, n=5500, ghc 6.8:
>
>     $ ghc -O -fglasgow-exts -fbang-patterns -optc-O3
>     -optc-march=pentium4 -optc-mfpmath=sse -optc-msse2  -optc-ffast-math
>     spec.hs -o spec_hs --make
>
> With inlinePerformIO:
>
>     $ time ./spec_hs 5500
>     1.274224153
>     ./spec_hs 5500  26.32s user 0.00s system 99% cpu 26.406 total
>
> As expected, and comparable to the shooutout result for the same N.
> With unsafePerformIO, the whole thing falls apart:
>
>     $ time ./spec_hs 5500
>     ^Cspec_hs: interrupted
>     ./spec_hs 5500  124.86s user 0.11s system 99% cpu 2:05.04 total
>
> I gave up after 2 minutes. This FFI peek/poke code, acting as an ST
> monad, under a pure interface relies on inlinePerformIO.

Thanks for pointing this out.

Xiao-Yong
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