mersenneforum.org 'Total time' value in Factor4
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 2010-11-13, 20:43 #1 Rodrigo     Jun 2010 Pennsylvania 2×467 Posts 'Total time' value in Factor4 Hello, I just (finally) completed running an exponent to 73 bits, and I have a question about the time reading that's given at the end. The "Total time" value is given as "414528.281 secs." Supposing that "secs." is seconds, then if I haven't forgotten completely how to do math, that amounts to (414528.281/60) = 6908.8 minutes, or (6908.8/60) = 115.146 hours. That would be less than four full days. But in fact the poor computer was patiently chipping away at this one exponent 24/7 since the first week of October, or close to a month and a half. So the question is -- what does that "Total time" value represent? In case it helps to find the answer, that PC (an older model) is running Factor4. Thanks! Rodrigo
2010-11-13, 23:30   #2
lavalamp

Oct 2007
Manchester, UK

17×79 Posts

Quote:
 Originally Posted by Rodrigo if I haven't forgotten completely how to do math That would be less than four full days.
Ahem.

But anyway, did you restart the PC and resume from a checkpoint part way through or something? Possibly it only records however long the last run was.

Alternatively, perhaps something else on the PC was using most of the CPU time, and factor4 only got to use the CPU for a combined total of 115.147 hours.

I also note that the time in seconds multiplied by 10 gives ~48 days, which is approximately a month and a half, maybe that is just a coincidence though.

2010-11-14, 00:18   #3
Rodrigo

Jun 2010
Pennsylvania

93410 Posts

Quote:
 Originally Posted by lavalamp Ahem.
lavalamp,

LOL! I guess that I have forgotten how to do math -- that's less than five days.

Quote:
 Originally Posted by lavalamp But anyway, did you restart the PC and resume from a checkpoint part way through or something? Possibly it only records however long the last run was.
The PC worked almost nonstop on this exponent since September 30, except for a four-day hiatus in mid-October when we went away on vacation. So I counted as of October 4, through today, 40 days.

Nothing else was going on on the PC, except for the security software (AV and firewall) and the occasional automatic definitions updates to it.

Now, I said that it ran "almost" nonstop, because I did restart the system a couple of times, closing Factor4 and then reloading it using the -r switch. Oh, and -- come to think of it -- we had a brief power outage exactly as long ago as Factor4 reports the "Total time" was! (Thank you, APC.) So the program was not properly shut down.

That must be the reason. Maybe Factor4 forgets how long it's been working on an exponent, if it doesn't get closed correctly.

Thanks lavalamp -- your idea led me to what no doubt is the answer!

Rodrigo

2010-11-14, 00:34   #4
mdettweiler
A Sunny Moo

Aug 2007
USA (GMT-5)

3×2,083 Posts

Quote:
 Originally Posted by Rodrigo That must be the reason. Maybe Factor4 forgets how long it's been working on an exponent, if it doesn't get closed correctly.
This is a rather common phenomenon with prime-crunching applications. For instance, LLR (a Prime95-based program for testing numbers of the form k*b^n+c) similarly only reported time elapsed since the last resume until its 3.8.0 release earlier this year, in which it started keeping track of that in the save file. AFAIK, it is still the only application of its kind to support such a feature.

 2010-11-14, 01:13 #5 Rodrigo     Jun 2010 Pennsylvania 11101001102 Posts mdettweiler, That's interesting! So, Factor5 must work like Factor4 in this regard. Not that it's a critical flaw or anything, just an obscure corner of the software to wonder about on a lazy Saturday... Rodrigo Last fiddled with by Rodrigo on 2010-11-14 at 01:13
 2010-11-14, 12:02 #6 ET_ Banned     "Luigi" Aug 2002 Team Italia 10010110010112 Posts Rodrigo, mdettwweller and lavalamp are right: the program only records the time elapsed since last restart. Luigi
 2010-11-14, 16:41 #7 Rodrigo     Jun 2010 Pennsylvania 2·467 Posts Luigi, Thanks for confirming! Rodrigo

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