Re: [Haskell-cafe] Substring replacements

From: Daniel Fischer To: "Branimir Maksimovic" CC: Haskell-Cafe@haskell.org Subject: Re: [Haskell-cafe] Substring replacements Date: Wed, 14 Dec 2005 17:10:20 +0100

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I think that's because on your machine Bulat's version have better perfromance with CPU cache. I don;t know but now your version is 25% faster with my test on P4 hyperthreaded.

Errrr, what's 'hyperthreaded' ? Unfortunately, I'm completely useless with computers.

I think that i've figure it now. Hyperthreading is hardware CPU feature that single CPU core can speed up execution of two running threads. For example if one thread uses integer unit and other FP unit CPU executes that in parallel. But that's not important or significant. What is interestenting is memory latency. If one thread peeks and pokes around memory for , say 1 unit of time, with usual CPU two thread will execute 2 units of time. Hyperthreaded (I'm talking about intel implementation) CPU will execute that in 1.4 points of time giving 60% boost in terms of speed. I've tested some assembler and C program that launches two threads each roaming over memory to anulate impact of cache. What is noticable is that two threads have 60% less memory latency constantly then single thread. That means if single thread for each out of cache memory access waits 300-400 CPU cycles, two threads wait 60% less. Now what has that to do with our programs as they are single threaded? I think it's garbage collection. Our programs run with garbage collector in background and you feel that burden by 20% as your program probably pushes garbage collector to work more than Bulat's version. On hyperthreaded CPU impact of garbage collection is reduced by a factor of 30-60 % resulting in your program being 30% faster on my machine. Greetings, Bane. _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/