#1984: weird performance drop with -O2 on x86
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Reporter: guest | Owner:
Type: bug | Status: reopened
Priority: normal | Milestone: 6.8 branch
Component: Runtime System | Version: 6.8.2
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: x86
Os: Linux |
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Changes (by simonmar):
* status: closed => reopened
* component: Compiler => Runtime System
* resolution: duplicate =>
Comment:
Actually I lied - there was more to this than I thought. With -O turned
on, the main thread was only allocating in forkIO, and it turned out that
the fork primitive (and primitives in general) don't check the context
switch flag, so we ended up creating lots of threads but not running any
of them, so they didn't get a chance to die and the heap filled up with
runnable threads causing GC to take a long time.
I have a fix for this in my tree, will commit in due course.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1984#comment:5>
GHC <http://www.haskell.org/ghc/>
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