20050907, 21:33  #1 
Sep 2005
UGent
2^{2}·3·5 Posts 
Wildly differing times for step 2 with ecm6.0.1
I recently started exploring GMPECM and noted that for a given number and given parameters, the Step 1 time is almost constant, but Step 2 time varies from run to run up to a factor 5 or so. This is on one and the same machine for 5 curves:
Code:
Step 1 took 1188420ms Step 1 took 1188460ms Step 1 took 1189800ms Step 1 took 1188310ms Step 1 took 1189760ms Code:
Step 2 took 671880ms Step 2 took 718610ms Step 2 took 2851240ms Step 2 took 475260ms Step 2 took 558580ms 
20050907, 21:38  #2 
"Nancy"
Aug 2002
Alexandria
2,467 Posts 
Stage 2 can use quite a lot of RAM. Is the computer running out of memory and starting to swap to disk a lot? In that case, the performance you'd get would depend i.e. on how many other applications are running.
What system are you on, what number are you factoring and with what parameters? Alex 
20050910, 08:11  #3 
Sep 2005
UGent
2^{2}×3×5 Posts 
Looking at a `top', I think I can explain the problem: a load average of 1.3 (should be 1.0). However, apart from `ecm' I see nothing else running... so that will require some investigation.
By the way: the machine is a PentiumIV 3.0GHz with 2GB ram and zero swap. The number is a C288, and I'm running ecm6.0.1 with B1=11e6. Other question: Is there any difference between running `ecm' ten times, as opposed to running once with a c 10 option? 
20050910, 09:23  #4  
Mar 2003
New Zealand
13·89 Posts 
Quote:


20050911, 21:25  #5  
Sep 2005
UGent
2^{2}×3×5 Posts 
The problem with differing times seems to have resolved itself by rebooting (I still don't know what caused it).
Quote:


20050911, 23:19  #6  
Jul 2004
Potsdam, Germany
3·277 Posts 
Quote:


20050912, 00:33  #7  
Mar 2003
New Zealand
13×89 Posts 
Quote:


20050912, 01:30  #8 
Mar 2003
New Zealand
13×89 Posts 
As a reference point, here is a curve for a general 284 digit number on a 2.66GHz P4:
GMPECM 6.0 [powered by GMP 4.1.4] [ECM] Input number is 1659 ... 8037 (284 digits) Using B1=11000000, B2=25577181640, polynomial Dickson(12), sigma=3150013712 Step 1 took 645928ms Step 2 took 208735ms 
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