#5536: IO performance regression in 7.2 vs 7.0
---------------------------------+------------------------------------------
Reporter: simonmar | Owner:
Type: bug | Status: new
Priority: high | Milestone: 7.4.1
Component: libraries/base | Version: 7.2.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
---------------------------------+------------------------------------------
The following program:
{{{
main = interact id
}}}
runs about a third slower in 7.2.1 compared to 7.0.3 (and current 7.3 is
about the same as 7.2.1).
With 7.2.1:
{{{
$ ls -l stuff
-rw-rw-r-- 1 simonmar GHC 128464904 2011-10-07 14:59 stuff
$ ./cat <stuff >/dev/null +RTS -s
8,357,007,912 bytes allocated in the heap
793,616,736 bytes copied during GC
83,984 bytes maximum residency (1 sample(s))
24,936 bytes maximum slop
1 MB total memory in use (0 MB lost due to fragmentation)
Tot time (elapsed) Avg pause Max
pause
Gen 0 15966 colls, 0 par 0.94s 0.94s 0.0001s
0.0001s
Gen 1 1 colls, 0 par 0.00s 0.00s 0.0004s
0.0004s
INIT time 0.00s ( 0.00s elapsed)
MUT time 5.71s ( 5.71s elapsed)
GC time 0.94s ( 0.94s elapsed)
EXIT time 0.00s ( 0.00s elapsed)
Total time 6.65s ( 6.65s elapsed)
}}}
and with 7.0.3:
{{{
$ ./cat <stuff >/dev/null +RTS -s
./cat +RTS -s
5,299,570,680 bytes allocated in the heap
250,350,336 bytes copied during GC
53,232 bytes maximum residency (1 sample(s))
30,776 bytes maximum slop
1 MB total memory in use (0 MB lost due to fragmentation)
Generation 0: 10086 collections, 0 parallel, 0.50s, 0.50s elapsed
Generation 1: 1 collections, 0 parallel, 0.00s, 0.00s elapsed
INIT time 0.00s ( 0.00s elapsed)
MUT time 4.38s ( 4.38s elapsed)
GC time 0.50s ( 0.50s elapsed)
EXIT time 0.00s ( 0.00s elapsed)
Total time 4.88s ( 4.88s elapsed)
}}}
I strongly suspect this has to do with the changes to the encoding
machinery in 7.2.1.
In binary mode, the slowdown is even worse. The program:
{{{
import System.IO
main = do
hSetBinaryMode stdin True
hSetBinaryMode stdout True
getContents >>= putStr
}}}
With 7.0.3 this runs in 3.35s, with 7.2.1 it takes 5.49s, a slowdown of
63%.
After fixing this, we need to add a performance regression test.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5536>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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