20170201, 19:36  #1 
"Geoffrey Yeung"
Feb 2017
London
2·3^{2} Posts 
Low CPU/GPU usage?
Hi, just started learning to use msieve, trying to run on a 170 digit number, but I notice CPU and GPU usage are both quite low. Is this normal?

20170201, 21:45  #2 
"Geoffrey Yeung"
Feb 2017
London
22_{8} Posts 
Sorry, apparently I forgot the attachment or something:
https://imgur.com/a/g3xFM I am in fact running factmsieve.py, after following instructions from that guide. I should be using the CUDA version if I did it correctly.I just started the process, so I'm still in the poly selecting stage. Here's the log file, if it's of any use: http://pastebin.com/0jitawas 
20170201, 21:53  #3 
I moo ablest echo power!
May 2013
1,747 Posts 
The GPU is used only for part of the np step (np1, if you look at the msieve h), so it's not being used 100% of the time. Not sure about the CPU since I think the other parts of np1 (nps and npr) are multithreaded. Maybe npr is not.
Also, based on your filename, are you trying to crack an RSA number? Might want to explain what you're doing... 
20170201, 22:10  #4 
"Geoffrey Yeung"
Feb 2017
London
2×3^{2} Posts 
As you mentioned them, can you explain the flags / process in a bit more depth? I'm still reading up on NFS very slowly...
As for the "RSA", we're learning cryptography in our computing class, and the 170 digit number is the example modulus used. I take this chance to try and crack it while reading up on some extra maths. I believe the standard for RSA nowadays is (or rather should be) 2048 bit anyway, and probably not this unusual 170 digit. 
20170201, 22:17  #5 
I moo ablest echo power!
May 2013
1,747 Posts 
Truthfully, there are others on here (including MSieve's creator) who can explain it better than I can, so I'll leave that to them.
I only asked about the RSA name because there have previously been others on here trying to crack keys. As you might imagine, people are less inclined to help them. Also, that C170 is going to take a while to factor using GNFS. I'm working on a C150 (with 6 threads), and that's going to take me a week or so. I believe the general rule of thumb is that time to factor via GNFS roughly doubles for each 5 digit increase, so you're looking at something like 4 months or so? 
20170201, 22:30  #6 
"Geoffrey Yeung"
Feb 2017
London
22_{8} Posts 
Thanks for the info, I'll keep looking around!
I wasn't sure how long will it take; your 4 months estimate is a bit high for me. My spring term ends at the end of March, and if I don't expect to finish cracking by then, I'll probably stop the project and go back to finding primes. I may be able to use my uni's computers to speed up the process a bit, but I'm not sure how effective can that be. 
20170201, 22:43  #7 
"Curtis"
Feb 2005
Riverside, CA
2^{2}×17×71 Posts 
Expanding on Wombatman's info:
Poly select can be run for as long as you like; I suggest about a GPUweek as a reasonable balance (that is, if you spent only 3 days on poly search you might spend 4 extra days on the other longer steps, compared to a better poly that the extra 4 days *might* find it's guesswork and expectations). Once that step is done,and you can run that step on different ranges of leading coefficients on multiple machines (say, 1 day each on 7 machines with each one assigned a range on the command line), then you'd invoke factmsieve.py with the proper number of threads for your machine's hardware. For best speed, DO take advantage of hyperthreading; a quadcore HT should have 8 threads running. Speed: I've finished a GNFS156 on a 6core i7 in nearly exactly 7 days. So, using the "double every 5 digits" rule of thumb, you can expect 78 weeks if you have 6 cores available, or 1012 weeks if you have just a single quadcore. You can definitely split the task over two or more machines; just make each machine do its own region of qvalues. If you look at the command that factmsieve issues to the command line as it runs, you can figure out how to manually invoke lasieve4i15e on any number of machines. It takes a little practice/trial and error; I suggest you try to factor something around 130 digits and mess with command lines and editing qvalues and renaming outputs to spairs.add to see how the script adapts to these things. If you post the number here, I'll give my GPU a few hours of poly select on it, and can explain what score means for your expected sieving time. Note the stage after sieving, when you solve the matrix, will be done on one machine only. Expect a few days for that last step (unless you have a really fast machine like a Xeon or 6core, which might reduce that to 5065 hr). Good luck! 
20170201, 23:04  #8 
"Geoffrey Yeung"
Feb 2017
London
2×3^{2} Posts 
If you're interested, here's the information for our given RSA encryption: http://pastebin.com/QTC4LpvJ
I'll mess around a bit more with the code on uni's computer tomorrow. I got so far as to figured out the escore(?) is the 10^13 one in .dat.p file; "rroots" is probably the number of real roots of the polynomial, and that smallest integer param is a good indication of progress. I'm progressing but struggling quite a bit understanding the ggnfsdoc.pdf, as I barely know any group theory. On the bright side, I'll have a quite a head start next year Again, thank you everybody for the information! 
20170202, 04:06  #9 
"Curtis"
Feb 2005
Riverside, CA
2^{2}·17·71 Posts 
I admit I don't grok the NFS algorithm as well as I'd like, but for your purposes it's quite useful to understand the stages and what progress looks like.
I'm running poly select on two GPUs this evening on your number; I'll let them each run a couple hours and post the best poly I find here (so you can compare what you find, which will surely be better). In this subforum, you'll find a thread "best msieve poly scores". Post #7 notes a C170 has best score 3.91e13. If you break that score, I'd end poly select and proceed right to the sieving step (and post the poly you found so I can note the new record!) A C171 has score of 3.13e13, so you should expect to beat that score with your search. Score is, roughly, a measure of the rate at which you can expect to find relations, so a larger score is better (and project length scales roughly with inverse of score a 3e13 project is *about* 10 times harder than a 3e12 project). Your search will produce quite a few okay polys, with occasional good ones. In some sense, we wait for a really good one to pop out of the search but how long to wait, as well as what "good" is, isn't quite clear. That's why I track best scores if you break someone else's best for a size, you've likely found a really good poly and can skip the rest of poly select. If you find a few around 3.2e13, and then one batch has one or two like 10% better, you've probably found your poly. It's worth holding out a few days of poly select for a hit 810% better than the typical best results from a run (I check twice a day, and consider each halfday a "run"), because 8% shorter project length for an 8week effort is ~5 days of saved sieving time. The factmsieve script has been tested and refined for inputs up to about 150155 digits; the automatically generated settings aren't the fastest for 150+ digits, simply because so few projects are done at those sizes the author lacked data to create a set of best parameters (so he guessed a little, and figured anyone serious enough to do C170 would already know enough to set parameters himself). The NFS@home BOINC project has recently done a bunch of factorizations in this size category, but they've not always optimized parameters for shortest project length; all the same, their parameters are useful to copy for this project absent better info. If you decide you wish to do this factorization, I'll explain testsieving in a future post, so you can test a couple possible parameters choices and hope to discover savings of a day or week in sieving via betterthanscriptdefault choices. Last fiddled with by VBCurtis on 20170202 at 04:09 
20170202, 05:51  #10 
"Curtis"
Feb 2005
Riverside, CA
2^{2}·17·71 Posts 
2 hrs on each of two GPUs yielded 5 polys between 3e13 and 3.1e13, one just over 3.1e13, and this one:
Code:
# norm 1.664492e16 alpha 7.157348 e 3.470e13 rroots 5 skew: 5053398.85 c0: 2786893278589734609571856633574386128995 c1: 4306299542743462566376217981723261 c2: 3783578211791106561032446613 c3: 821977447850264829373 c4: 149300456419050 c5: 5352984 Y0: 387655707969523635036413081890624 Y1: 16516041263376677 ./msieve np1 nps "5000000,6000000 stage1_norm=4e24 stage2_norm=4e22" s rsa170test When I got bored, I stopped it and then ran: ./msieve npr s rsa170test The 5million,6million part is the value of the first coefficient to search over; this is the part you can easily spread over multiple machines. The other settings I set based on personal experience and the speed of my GPUs. Hope this helps! 
20170202, 08:50  #11 
"Geoffrey Yeung"
Feb 2017
London
2·3^{2} Posts 
Sorry, I think I set up something wrong.
I ran the poly sel overnight (~16 hour total), and the best poly is slightly less than 3e13, and you have few over 3e13 in few hours. The test also only ran from 0 to ~400 for the leading coefficient, instead of your 5 million. Perhaps because I invoked it through factmsieve.py, instead of using custom parameters? Again, the CPU / GPU usage is consistently low (~50% at best), is that normal? Lastly, I tried to run '.\msieve np1 nps "6000000,7000000 stage1_norm=4e24 stage2_norm=4e22" s RSA', it complains "cannot open input file 'worktodo.ini'". I tried to make a worktodo.ini with the C170 number in it and see what happen. It creates a .ms file, it runs and outputs log on the command prompt, but it has yet to output anything. When I interrupted it, it shows "error generating or reading NFS polynomials". All files remain empty / unchanged Sorry for the bombard of questions Last fiddled with by GeoffreyY on 20170202 at 08:50 
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