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Old 2008-11-19, 19:06   #1
testi
 
Nov 2008

3 Posts
Default ICC performance gain

Hello, just out of interest i compared msieve performance when compiled with ICC and gcc 4.3.

Hardware :
model name : Intel(R) Core(TM)2 Duo CPU E8500 @ 3.16GHz
ram : DD2 8500

Software:
gcc (Debian 4.3.2-1) 4.3.2
icc (ICC) 11.0 20080930

Flags :
gcc : -O3 -fomit-frame-pointer -march=core2 -D_FILE_OFFSET_BITS=64
icc : -fast -fp-model precise -D_FILE_OFFSET_BITS=64

GMP was used, compiled with gcc (I could'nt get it to compile with ICC before giving up)


Number to be factored (random 100 digits number generated with openssl):
1802716097522165018257858828415111497060066282677325501816640492782221110851604465066510547671104729

I tried to be as fair as possible and copied the factor base from the first run (gcc) for the icc run and fixed the random number in the source.

Results :
GCC :
Code:
Mon Nov 17 03:29:59 2008  prp50 factor: 38589340584901213653958931179714585367490014795273
Mon Nov 17 03:29:59 2008  prp50 factor: 46715390058453362424711065024780497160328505582673
Mon Nov 17 03:29:59 2008  elapsed time 31:46:11
ICC:
Code:
Tue Nov 18 13:39:01 2008  prp50 factor: 38589340584901213653958931179714585367490014795273
Tue Nov 18 13:39:01 2008  prp50 factor: 46715390058453362424711065024780497160328505582673
Tue Nov 18 13:39:01 2008  elapsed time 27:00:43
Full logs are attached
Attached Files
File Type: bz2 logs.tar.bz2 (4.9 KB, 77 views)
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Old 2008-11-19, 21:28   #2
jasonp
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Oct 2004

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Thanks, that's good to know. Brian Gladman has kindly performed a complete overhaul of the preprocessor defines for compiler-specific inline asm, so that the next version will allow icc to reuse all the gcc-specific assembly language. I suspect that it currently does not.

Was this a 64-bit or 32-bit binary?
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Old 2008-11-19, 22:45   #3
testi
 
Nov 2008

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64 bits.
Do you mean msieve will use gcc intrinsics ?

I have seen with other programs that ICC register allocator and optimisations are dramatically more efficient than gcc (for SSE2)
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Old 2008-11-19, 23:41   #4
jasonp
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I meant using gcc-format inline asm statements, which according to Brian can be parsed by icc. He also reports favorable speedups on windows.
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Old 2008-11-19, 23:46   #5
testi
 
Nov 2008

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maybe it would be worth trying intrinsics, i'll try to check if I have time
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Old 2008-11-20, 03:00   #6
jasonp
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Actually, Intel's compiler could probably benefit from a prefetch intrinsic. The code has gcc and MSVC versions but no icc version in include/util.h
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