Hi all,
I'm working on prime95 version 20. The important new feature
is a P-1 factoring step prior to a Lucas-Lehmer test. The P-1 factoring
step has a 3-5% chance of finding a factor at a cost of 2-4% of an LL test.
The net effect is we speed up GIMPS' throughput by a percent or two (more
if you factor in the fact that a double-check is avoided too).
Stage 2 of P-1 factoring requires more memory than an LL test.
The more memory you give the program the faster stage 2 executes.
For example, an exponent around 10 million requires about
4MB of data. P-1 stage 2 would like to have 48MB, but can get by with
as little as 24MB. The good news is that the LL test takes a month, P-1
factoring takes a day, and the memory hungry stage 2 takes only half a day.
GIMPS has always had a good reputation for not interfering with
your normal work. To preserve GIMPS' reputation, I'm thinking of implementing
the following. In the Options/CPU dialog, prime95 will let you select the
maximum
amount of memory the program can use and the hours of the day it can use it.
The default would be 80% of RAM (divided by the number of CPUs) during
nighttime hours only.
Finally, the questions:
Would we be better off disabling P-1 factoring unless the user explicitly
activates it (knowing that most users won't read enough to turn it on)?
Are there better solutions? It would be nice if prime95 could detect that
memory thrashing was happening and pause itself until more memory
was available. Can Windows programs do this?
Are the defaults too aggressive (especially the 80% of RAM)?
You can send your comments and suggestions to me privately
or to the entire mailing list.
Having fun,
George
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