20190604, 05:25  #1 
Oct 2007
London, UK
1,297 Posts 
P1 on OBD candidates
Does anyone know of some utility that can handle P1 on these monsters?
v29.8 of prime95 says it only accepts exponents up to 595,800,000, which I assume corresponds to its maximum FFT size. A few years ago LaurV made a post about potentially implementing P1 in CUDA which sounds encouraging, but I don't know if he or anyone else got much further. https://www.mersenneforum.org/showpo...3&postcount=11 At least Prime95 can give optimal bounds for P1. If I put in a candidate TF'd to 86 bits, it recommends B1=B2=44,680,000, no stage 2 due to RAM limitations I believe. This doesn't sound completely unreasonable, and offers a 3.53% chance of a factor, this is slightly higher than the chance of a factor from continuing TF up to 89 bits (3/89 ~ 3.37%). If I say the candidate has been TF'd to 91 bits instead (which seems to be vaguely where GPU TFing should probably stop), then Prime95 offers the bounds B1=B2=30,920,000 with a 2.07% chance of a factor. Seems a bit odd to me that the bounds are LOWER when TF has progressed more, but alright. 
20190604, 06:00  #2  
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
111011110110_{2} Posts 
On an FMA3capable system prime95 should be capable of going to 920M (50M fft since V29.2). I'm running 701M now on 29.7b1 x64.
https://www.mersenneforum.org/showpo...&postcount=218 CUDAPm1 has been around for years but doesn't reach that high, due to various issues, although it nominally supports sufficiently large fft lengths, on gpus with sufficient ram. https://www.mersenneforum.org/showthread.php?t=23389 Quote:
Last fiddled with by kriesel on 20190604 at 06:26 

20190604, 06:10  #3 
Oct 2007
London, UK
10100010001_{2} Posts 

20190604, 06:46  #4  
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
2·5·383 Posts 
Quote:


20190604, 08:05  #5 
Oct 2007
London, UK
1,297 Posts 
Perhaps in time the limits will be raised such that stage 1 for these numbers will be possible. Though I completely understand why enabling such functionality is not exactly top priority.
For the memory usage, is there any possibility that it could be lowered if the second stage was broken down into multiple chunks, similar to stage 2 of ECM? 
20190611, 19:24  #6  
"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest
2·5·383 Posts 
Quote:
Of course, they are all going to be impacted by the roughly p^{2.2} run time scaling also. The 701M P1 run on my i78750H (all cores one worker) took 32.3 days at NRP~25, while a recent 430M P1 on a 3GB GTX1060 took ~5. days at NRP=5 (for both stages, no factor found). Those would scale to ~989. days and ~449. days respectively, per P1 on a gigadigit candidate. Note that run time also lengthens when NRP goes toward 1 due to memory size limitations. (CUDAPm1 reference info https://www.mersenneforum.org/showthread.php?t=23389 re prime95 see https://www.mersenneforum.org/showthread.php?t=23900) Last fiddled with by kriesel on 20190611 at 19:26 

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