RE: Re[2]: [Haskell-cafe] Re: Haskell Speed

From: Bulat Ziganshin Reply-To: Bulat Ziganshin To: "Branimir Maksimovic" CC: igouy@yahoo.com, haskell-cafe@haskell.org Subject: Re[2]: [Haskell-cafe] Re: Haskell Speed Date: Fri, 30 Dec 2005 17:56:57 +0300

Hello Branimir,

Friday, December 30, 2005, 3:44:26 AM, you wrote: BM> myHashString = fromIntegral . ff''' . ff'' . ff' . foldr f 0

i use the following hash function in my program:

filenameHash = fromIntegral . foldl (\h c -> h*37+(ord c)) 0

(it's written without explicit parameter in order to try to help GHC machinery better optimize this function)

I've found that hasing function and anything that does calculation is fast enough (compared imported C function and Haskell, and no real difference, Haskell is fast regarding calculations) , problem is with memory leak. In this case hashing function have to be strong in order to avoid linear search. when memory leak with HashTable dissapears I will use some even better hash functions.

BM> All in all functional version consumes less memory and is twice as BM> fast.

IOArrays is second-class citizens in GHC/Haskell. they are scanned on _each_ GC, and this can substantially slow down program which uses large IOArrays.

Hm, there is Hans Boehm GC for C and C++ and I have gcmalloc and gcmalloc_atomic. Why this isn;t present in Haskel? gcmalloc_atomic is usefull when allocating large arrays that does not contain any references/pointers.

for your program, things will be not so bad because IOArray, used inside your HashTable, contains far less than million elements and because your program has more to do itself. but try to compare MUT time of functional and imperative version - may be your algorithm is really faster and only GC times makes this comparision unfair

Hm that can be solved if hash_table use gcmaloc_atomic I guess. (If all execution times goes for GC scans).

.. writing this message i thought that reducing number of GCs can speed up my program and your program too. so there is third variant - using IOArray, but with "+RTS -A100m"

Wow, that option almost doubled speed of HashTable program (memory leak remains). Thank you, for enlighten me about GC. After this I can think of gc_add_scanrange,gc_remove_scanrange and gcmalloc_atomic functions as they are now common to other languages? We need low level GC interface in order to produce fast programs. Greetings, Bane. _________________________________________________________________ Don't just search. Find. Check out the new MSN Search! http://search.msn.com/