weird performance drop with -O2 on x86
Here's my program:
import Control.Concurrent
import Data.IORef
maker :: IORef Int -> IO ()
maker v = loop
where
loop = do
x <- readIORef v
writeIORef v $! x + 1
forkIO (return ())
loop
main :: IO ()
main = do
v <- newIORef 0
t <- forkIO (maker v)
threadDelay 1000000
killThread t
x <- readIORef v
print x
It's supposed to print the number of threads created in one second. With ghc -O2, I get around 61104; similarly for -O1. However, with no optimization I get results around 612274, i.e. approximately ten times more threads in the same time. What's going on here?
More data points:
- 6.1 behaves similarly but the numbers are a bit higher (~10% more iterations).
<dons> be sure to mention that results appear normal on amd64.
Trac metadata
Trac field | Value |
---|---|
Version | 6.8.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |