Re: Re[2]: [Haskell-cafe] Haskell performance question
On Nov 8, 2007 10:28 PM, Bulat Ziganshin [EMAIL PROTECTED] wrote: just for curiosity, can you try to manually unroll loop and see results? I don't get any noticeable performance change when I unroll the loop by 2 by hand. I suspect that on a modern CPU loop unrolling probably isn't that much of a win. I'm more interested in strength reduction, especially when computing things like indices into multidimensional arrays. Anyone know how well ghc performs in this area? -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Haskell performance question
Hello Don,
Thursday, November 8, 2007, 10:53:28 PM, you wrote:
a - newArray (0,n-1) 1.0 :: IO (IOUArray Int Double)
forM_ [0..n-2] $ \i - do { x - readArray a i; y - readArray a
(i+1); writeArray a (i+1) (x+y) }
oh, i was stupid. obviously, first thing you need to do is to use
unsafeRead/unsafeWrite operations. i'm wonder how this code is only
20x slower than C version, may be you need to use gcc -O3 -funroll-loops
and gcc3 (because gcc4 becomes slower)
--
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Bulatmailto:[EMAIL PROTECTED]
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Re[2]: [Haskell-cafe] Haskell performance question
Hello Dan, Thursday, November 8, 2007, 10:12:04 PM, you wrote: The strictness gave me something like a 10% performance increase making the Haskell code more than 10 times slower than the C. Is this the right type of array to use for performance? yes. but ghc is especially slow doing FP arithmetics. in my own simple test ( a[i]=b[i]+c[i] ) it's 20x slower than gcc, so your results aren't surprising -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Haskell performance question
Hello Xiao-Yong,
Thursday, November 8, 2007, 10:41:11 PM, you wrote:
forM_ [0..n-2] $ \i - do { return $! i;
x - readArray a i; return $! x;
y - readArray a (i+1); return $! y;
writeArray a (i+1) (x+y) }
such cycle should be approx. 3-10 times slower than C one
I didn't know you can do that. Anyway, I tried OP's C and
Haskell versions and the one with your strictness
annotations. It seems that the `$!' thing doesn't do much,
or it's not doing anything.
i don't said that it will help, just that it may help. to know
exactly, one should either understand ghc strictness analyzer, or
check asm code
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Re[2]: [Haskell-cafe] Haskell performance question
Hello Dan, Friday, November 9, 2007, 3:58:42 AM, you wrote: HSbase-3.0.0.0.o but I was able to rerun the timings for my code. WIth -O2 the run time went from about 1.5s to 0.2s. With unsafeRead and unsafeWrite that becomes 0.16s. cool! seems that small loops now are runs on registers, in 6.6 each step of such loop was about 50 instructions long, fetching everything from memory just for curiosity, can you try to manually unroll loop and see results? btw, this still doesn't mean that ghc can be used for numeric-intensive code - it should be tried on larger code blocks. but definitely, it's a whole new era in low-level ghc programming -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
