Thread: ECM work vs LL work View Single Post
2018-10-10, 22:18   #6
kriesel

"TF79LL86GIMPS96gpu17"
Mar 2017
US midwest

13FB16 Posts

Quote:
 Originally Posted by irowiki Well I've had a few machines where Primenet detects them as P4 100mhz equiv to start, assigns them ECM work, and then after a while of ECM work, it realizes that "oh, this is actually a 5 ghz P4 equiv, here, have a doublecheck" The only machine I had only get ECM work only was an Atom Netbook that I brought on as a test, and it took it days to do one assignment so I retired it. I started in august, every machine I've brought online (almost 50) has done a few doublechecks then moved on to a LL check. Oddly, when I bumped everything up to "get 10 days of work" they got confused and heaped on more doublechecks. Edit: so P-1 Factoring helps weed out things so the LL tests are better, and I should get machines with a ton of ram and make them do P-1 tests?
For the basics see https://www.mersenne.org/various/works.php and https://www.mersenne.org/various/math.php
P-1 factoring bounds are tested for each run for the values which give optimal time savings given the probabilities of finding a factor or not, given the estimated time costs of P-1 factoring versus performing a number of LL or PRP tests on the exponent. P-1 done extensively may save the project time. But the system time you allocate to P-1 factoring won't find a Mersenne prime, although it may find some impressively large factors.
P-1 and PRP are performed with very similar calculations (3 raised to a power mod the Mp using DP fft transforms), and LL is close too, so the credit per cpu hour expended is close. If P-1 takes 1/40 the time of a primality test and has a 3% chance of a factor, you'll get 1000 P-1 factored in the time it takes to do 25 primality tests, and find about 30 factors, eliminating the need for ~30-60+ primality tests. (First LL, LL DC, and the occasional third test when residues don't match, for 60+. Or 30 PRPs.) So the project would be 5 primality tests ahead in that hypothetical case.
P-1 speed is helped by more RAM available to it, in stage 2. But slow machines can run it with 1GB available, at the current wavefront.
Double checks are welcome both because they test a system's reliability and because they help cut down on the growing double-check backlog.