2018-10-11, 16:08 | #1 |
Sep 2009
2^{3}×7×43 Posts |
Multithreaded Linear Algebra threshold
By default msieve only uses multiple threads for matrices with more than 200000 columns. I've found this causes a step in the run time to solve a matrix:
Code:
grep -e ' lanczos halted' -e BLanczosTime -e 'commencing L' f*/ggnfs.log | less ... f600_51+3/ggnfs.log:Tue Oct 9 21:48:53 2018 commencing Lanczos iteration (4 threads) f600_51+3/ggnfs.log:Tue Oct 9 21:49:40 2018 lanczos halted after 3203 iterations (dim = 202523) f600_51+3/ggnfs.log:Tue Oct 9 21:49:41 2018 BLanczosTime: 60 ... f61_80+7/ggnfs.log:Wed Oct 10 01:50:19 2018 commencing Lanczos iteration f61_80+7/ggnfs.log:Wed Oct 10 01:52:15 2018 lanczos halted after 3134 iterations (dim = 197959) f61_80+7/ggnfs.log:Wed Oct 10 01:52:15 2018 BLanczosTime: 128 Code:
chris@vega:~/msieve-svn/trunk> diff common/lanczos/lanczos.h ~/msieve-svn.old/trunk/common/lanczos/lanczos.h 98c98 < #define MIN_NROWS_TO_THREAD 100000 --- > #define MIN_NROWS_TO_THREAD 200000 On the same system after the change: Code:
f791_47+6/ggnfs.log:Thu Oct 11 15:24:58 2018 commencing Lanczos iteration (4 threads) f791_47+6/ggnfs.log:Thu Oct 11 15:25:39 2018 lanczos halted after 2973 iterations (dim = 187904) f791_47+6/ggnfs.log:Thu Oct 11 15:25:39 2018 BLanczosTime: 51 That system has 4 real cores, no hyperthreading. On another system where msieve is running on 1 core and it's hyprethreaded partner there's no step in run times. Note it's only worth doing if you are factoring a lot of numbers with a matrix in this size range. And you do need to check if it will help on the system you are using. Chris |
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