Brian Beesley writes (re. Mfactor):
> I found that Mfactor on a 21164 was significantly
> faster than Prime95 on a system which runs LL tests at
> about the same rate. However the operational
> inefficiencies caused by driving Mfactor manually
> were outweighing this even before an improved LL
> tester for the Alpha platform came along (Thanks!)
Re. the manual aspect, Martijn Kruithof suggests
> We are talking unix here aren't we?
>
> You could make an input file with the factors (As you
> must enter them, including any stuff you must enter
> before you enter the first factor) and then run
> mfactor in the background
>
> nohup mfactor < input.file > output.file &
>
> then you can log out.
..which significantly eases the manual aspect, but not
the automatic reporting one.
I wrote:
> > I think the suggestion to have one machine (whether
> > that be a PC running Prime95 or a MIPS or Alpha
> > running Mfactor) do all the factoring needed to keep
> > multiple non-PC machines well-fed with exponents is
> > a good one, since otherwise, juggling factoring and
> > LL work becomes a pain.
to which Brian replies:
> Yes. Despite the inefficiency I find the best thing to
> do is to use an Intel PC running mprime/linux or
> Prime95/windoze to do the factoring. The point is one
> can simply take the worktodo.ini lines off PrimeNet
> (manual testing), change "Test" to "Factor" & stuff
> the file into George's program - without even
> bothering to check the factoring limits. Those that
> are already factored deep enough just get thrown out
> straight away.
>
> This is even more the case since v20 with P-1 factoring
> capability came out. Now one changes
>
> Test=<exponent>,<depth>
>
> to
>
> Pfactor=<exponent>,<depth>,0
>
> or
>
> DoubleCheck=<exponent>,<depth>
>
> to
>
> Pfactor=<exponent>,<depth>,1
>
> & waits for any neccessary trial factoring plus the
> P-1 factoring to be run.
>
> A P100 running (trial & P-1) factoring will easily
> keep a couple of PII-400s (or equivalent) busy running
> nothing but LL tests. The other advantage of doing it
> this way is that the the factoring system will report
> results to PrimeNet for you, automatically if you so
> choose.
Sounds like the right way to go to me, unless one has a
fast Alpha and really wants a thrills-a-minute kind of
ride. Note that the 21064 and 21164 are not as fast at
factoring as the 21264, but it seems a shame to have a
big fat L2 cache (the 21264s typically have 4 or 8MB)
and not use it (Mfactor gains very little in speed from
a large L2, since on the 21264, the 64MB L1 cache is
already big enough to hold a decently large small-primes
sieving table).
Come to think of it, factoring would be an excellent
application for a 21264 without an L2 cache, but I don't
know if they come that way (except perhaps in a
massively parallel setting, where the problem of
maintaining cache coherency in a multilevel cache
hierarchy often is nearly intractable). Then again, if
one turned a MP machine to factoring, GIMPS might soon
run out of factoring assignments, which would not please
those with 486s and other slower CPUs whose only useful
contribution to GIMPS is factoring.
Cheers,
-Ernst
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