#4450: Do stack squeezing before expanding stack
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.12.3
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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The presenting effect is that `nofib/spectral/hartel/genfft` exhibits non-
deterministic allocation behaviour:
{{{
./fft-noticky 7 +RTS -sstderr
13735234/185243
112,177,208 bytes allocated in the heap
61,405,448 bytes copied during GC
15,156,968 bytes maximum residency (8 sample(s))
13,590,616 bytes maximum slop
40 MB total memory in use (8 MB lost due to fragmentation)
Generation 0: 151 collections, 0 parallel, 0.10s, 0.10s elapsed
Generation 1: 8 collections, 0 parallel, 0.06s, 0.06s elapsed
INIT time 0.00s ( 0.00s elapsed)
MUT time 0.08s ( 0.08s elapsed)
GC time 0.16s ( 0.16s elapsed)
EXIT time 0.00s ( 0.00s elapsed)
Total time 0.25s ( 0.25s elapsed)
%GC time 66.3% (66.8% elapsed)
Alloc rate 1,343,359,176 bytes per MUT second
Productivity 32.9% of total user, 33.1% of total elapsed
-----------------------------
./fft-noticky 7 +RTS -sstderr
13735234/185243
114,257,976 bytes allocated in the heap
61,405,448 bytes copied during GC
15,156,968 bytes maximum residency (8 sample(s))
14,622,696 bytes maximum slop
40 MB total memory in use (6 MB lost due to fragmentation)
Generation 0: 151 collections, 0 parallel, 0.11s, 0.11s elapsed
Generation 1: 8 collections, 0 parallel, 0.06s, 0.06s elapsed
INIT time 0.00s ( 0.00s elapsed)
MUT time 0.08s ( 0.08s elapsed)
GC time 0.17s ( 0.17s elapsed)
EXIT time 0.00s ( 0.00s elapsed)
Total time 0.25s ( 0.25s elapsed)
%GC time 66.4% (66.8% elapsed)
Alloc rate 1,354,200,704 bytes per MUT second
Productivity 32.9% of total user, 33.0% of total elapsed
}}}
The non-determinism goes away with the RTS opt `-V0`.
In discussion we think the allocation differs because stack-squeezing
happens differently in the two runs.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4450>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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