#7429: Unexplained performance boost with +RTS -h
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Reporter: simonmar | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.8.1
Component: Compiler | Version: 7.6.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Runtime performance bug
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonmar):
I suspect it's a weird caching effect. The program creates a small data
structure and then repeatedly traverses it (if I'm understanding
correctly). After a GC the program performs much better, which suggests
that the GC has rearranged the data in memory in a more cache-friendly way
(not deliberately, I should point out). Or perhaps the data rearrangement
has avoided some cache conflicts, but that seems unlikely - L1 caches are
usually very associative.
You should be able to get the same effect by adding a performGC after
allocating the data structure but before traversing it.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7429#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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