P-1 coordination thread - discussion

[SlicerAce]

Can someone tell me how to use multiple worker threads in Prime95 on Windows XP? I am using mprime on another machine, and the nice thing about it is that I only start one instance of mprime and it creates two worker threads for the dual-core processor I have in that machine.

I have a dual-core processor on this machine as well, but it runs windows, and I have had a heck of a time trying to figure out how to get Prime95 to do the same thing. I think I found something that said that it's possible to do this on the Windows version, but there aren't any details how. People also make reference to stress testing where multiple threads are executed simultaneously.

One other nice thing about the multiple threads is that when one thread is in stage 2 and using lots of memory, the other thread will try to find other stage 1 work to do as not to use up even more system memory.

My question basically revolves around the worktodo.ini file structure. In the mprime version of the program, the structure is as follows:

[Worker #1]
Pminus1=blah blah blah
Pminus1=blah blah blah

[Worker #2]
Pminus1=blah
Pminus1=blah

and the program automatically recognizes what work is assigned to which thread. I tried putting this structure into the Prime95 worktodo.ini, but to no avail. Has anyone gotten this to work?

Update: Nevermind. I now find that the official release version of Prime95 does not support multithreading, while the latest version (25.4), available on the Mersenne Forums, does support multithreading. This is nice from the standpoint that it can start multiple threads and one can designate each thread to run on a separate core, but apparently the author had to make a change to the p-1 save file format to allow for larger B2 bounds, so the save file formats are not compatible. Anyone considering upgrading should keep this in mind -- finish up both stages of a number using the old client and THEN switch

On another note, does anyone have any information regarding the justification behind choosing B1 and B2 bounds? How do we estimate the probability that on a given number of the form k*2^n+1, a B1/B2 pair of bounds gives ____ % chance of finding a factor? A screenshot from an old version of Prime95 on someone's web site shows this estimate in the output of the program, but it appears that this is not in the final version. Even a rough estimate would be useful for getting a hold on these B1 and B2 bounds...