MilkyWay@Home, my main BOINC GPU project, was out of workunits for about 32 hours, so today I briefly crunched PrimeGrid. PrimeGrid is my backup BOINC GPU project, its resource share is 0%, so it kicks in only when MilkyWay@Home is completely out of work.
When you set resource share to 0, you will get no tasks for that BOINC project, as long as there are any other tasks running. When all BOINC projects with higher resource shares are exhausted and your GPUs go completely idle, only then the resource share zero project is contacted. That makes it an ideal setting for your backup BOINC project(s).
I have configured PrimeGrid to run only GFN-15 (looking for primes in the form of b215+1) and GFN-16 tasks (looking for primes in the form of b216+1). Such numbers are called Generalized Fermat Numbers or GFN. Those are quite short tasks (they take only a couple of minutes on any decent GPU), so you can crunch plenty of them in a short period of time. In 32 hours, I crunched 2941 GFN-15 tasks and 462 GFN-16 tasks with 6 HD7970 GPUs. Crunching so many tasks increases your chances of getting that special one, which contains a yet undiscovered prime number.
And indeed, I discovered one such number today: 62537488^32768+1. It's 255464 digits long, full decimal representation is here. By today's standards, that's not a very large prime number, but a nice discovery nevertheless. Such numbers get published on PrimeGrid front page (under 'Newly reported primes'), on GFN Prime Discoveries forum thread and on prime number list associated with my account. Larger primes also get published on The List of Largest Known Primes, under your own name (if you choose so, through your PrimeGrid account settings).
My computer 293682 needed 211.53 secs to crunch this lucky workunit on a HD7970 GPU. Other computer 515810 (GeForce GTX 560 Ti) crunched it almost twice as fast. That's not surprising, PrimeGrid FP32 GPU tasks were always better suited for Nvidia GPUs. Nevertheless, I managed to report this result first because I intentionally keep my work queue very small, so it gets crunched ASAP, waiting exactly for an opportunity like this. Careful tuning beats raw computing power for once :)
Literally as I was writing this post, MilkyWay@Home admins apparently fixed the problem and workunits are flowing there again. So, back to mapping the Galaxy, with another prime number acquired! Always plenty of interesting stuff going on in the world of computational science.
Of course, both MilkyWay@Home and PrimeGrid are whitelisted by Gridcoin, meaning you can also earn cryptocurrency while crunching for science and discovering things. Meaningless PoW hashing is a thing of the past (or will be soon).
