P-1 RAM usage and "E=6"
 

I have 2 machines doing basically nothing but P-1. I notice that one of my machines (both have 1GB RAM) seems to take full advantage of the ~920MB allocated, and I get "E=6" (which I understand means that Prime95 has more memory available than is required, therefore it runs P-1 longer/faster/deeper than it would if it had less memory) on all results, but my other machine only uses about 840MB, even though it's allocated 920MB, and I (usually) don't get "E=6" on any of the results. Any idea on what causes this, and how I can get better RAM utilization?

Borrow some RAM from another computer for 5 min, set up Prime95 to use all of it, then take it out, and Prime95 will adjust itself. One warning, you may have to re-activate Windows as it's a "major change in hardware."

[QUOTE=James Heinrich]I have 2 machines doing basically nothing but P-1. I notice that one of my machines (both have 1GB RAM) seems to take full advantage of the ~920MB allocated, and I get "E=6" (which I understand means that Prime95 has more memory available than is required, therefore it runs P-1 longer/faster/deeper than it would if it had less memory) on all results, but my other machine only uses about 840MB, even though it's allocated 920MB, and I (usually) don't get "E=6" on any of the results. Any idea on what causes this, and how I can get better RAM utilization?[/QUOTE]

Just let prime95 do its thing and don't worry about it. It is a pretty complex formula for choosing how much RAM to use in stage 2.

[QUOTE=Mike]Borrow some RAM from another computer for 5 min, set up Prime95 to use all of it, then take it out, and Prime95 will adjust itself.[/QUOTE]Tried that (put another 512MB in, let Prime95 use 1381MB (max allowed)), but no change. The only difference I got was that B2 was calculated to 197500 "but using 195000 from the save file".

I should probably mention that Stage-1 for these exponents was done with a 32MB limit on a machine that had very little memory, so I assume this is an after-effect of that. In a week or so I'll get through this set and onto some new exponents that haven't had stage-1 done yet, so I'll see what happens then.

[QUOTE=James Heinrich]Stage-1 for these exponents was done with a 32MB limit on a machine that had very little memory, so I assume this is an after-effect of that.[/QUOTE]
No, stage 1 uses very little memory, less than 32 MB, so that wasn't a problem.

The memory amounts you specified are only used for stage 2. Stage 1 doesn't need them.

[QUOTE=cheesehead]The memory amounts you specified are only used for stage 2. Stage 1 doesn't need them.[/QUOTE]Of course, I know that :smile:

But I theorize that if Prime95 runs stage1 and it only has a max of (for example) 32MB, it will write something different to the savefile than it would if it was allocated 920MB (even if it only uses very little memory during stage 1).

[QUOTE=James Heinrich]Of course, I know that :smile:[/quote]
Oh, sorry.

[quote]But I theorize that if Prime95 runs stage1 and it only has a max of (for example) 32MB, it will write something different to the savefile than it would if it was allocated 920MB (even if it only uses very little memory during stage 1).[/QUOTE]
No.

I can't believe I didn't check [i]prime.ini[/i] and notice that [b]OnlyRunStage2WithMaxMemory=1[/b] was missing from the machine in question... :whistle:

I think that may be the problem... let's see if it fixes it :smile:

[QUOTE=James Heinrich]I can't believe I didn't check [i]prime.ini[/i] and notice that [b]OnlyRunStage2WithMaxMemory=1[/b] was missing from the machine in question... :whistle:

I think that may be the problem... let's see if it fixes it :smile:[/QUOTE]

It won't. That only applies to machines where daytime memory is different from nighttime memory setting. If they are different stage 2 is only run at night when the extra memory is available.

I have 32MB allocated during "daytime" hours, 920MB allocated at "night" (the exact distribution of day/night is somewhat complex, as described in [url=http://www.mersenneforum.org/showpost.php?p=46723&postcount=8]this thread[/url]).

Sure enough, after changing [i]prime.ini[/i] I now have lines showing [b]E=6[/b] (and it's now using about 900MB instead of 840MB).