20060919, 12:17  #67 
"James Heinrich"
May 2004
exNorthern Ontario
110100100001_{2} Posts 
Could you please explain (briefly) what benefit more allocated memory gives? It says something about processing more relative primes when more memory is available. But what does it mean? I assume there's no greater chance of finding a factor, so it would have to be a speed improvement? How much better is it to process 20 relative primes compared to 10, for example? Basically, what do I get out of allocating 1500MB to P1 vs just 500MB?

20060919, 13:35  #68  
P90 years forever!
Aug 2002
Yeehaw, FL
2^{2}×1,873 Posts 
Quote:
The extra memory helps in several ways: As you noticed it processes more relative primes at a time. If there are 480 to process and process 20 at a time, then it takes 24 passes vs 48 passes if only 10 are processed at a time. There is a small fixed cost to do a pass so you save 24 times this fixed cost. Extra memory also helps by allowing prime95 to choose a 2nd pass that uses more relative primes. Prime95 processes from B1 to B2 in groups of 30 (2*3*5) or 210 (2*3*5*7) or 2310 (2*3*5*7*11). There are 8, 48, or 480 relative primes respectively. The bigger the group, the less fixed cost in counting from B1 to B2. We see above that using lots of memory, reduces the cost of processing from B1 to B2 a little bit. Therefore, it may pay to increase the B2 bounds a little bit to increase the chance of finding a factor. Finally, if you have lots of memory prime95 uses Suyama's trick to also include some factors above B2 at a small cost. It is an open issue whether extra small chance of finding a factor is worh this small cost. The above isn't real helpful. In short, you get a real big benefit when you go from a tight memory situation to a decent memory allocation. You get a tiny gain going from a decent memory allocation to a generous one. Last fiddled with by Prime95 on 20060919 at 13:38 

20060919, 14:31  #69  
Jun 2005
2·191 Posts 
Quote:
Is there an easy way to determine where the knee is in the cost vs. benefit curve? I assume it depends on the size of the exponent. I want to test things as effectively as I can, but I must say that P1 stage 2 is the only part of Prime95 that can be intrusive at times, such as when I run another memoryintensive task. Perhaps there can be a 'smart memory' setting that will determine the most reasonable value as long as it's below the allocated memory setting. Drew 

20060919, 17:44  #70 
Oct 2004
Austria
2482_{10} Posts 
Can Prime95 version 25 handle bigger B2 values than 4290M (for ECM and P1)?

20060919, 19:21  #71 
P90 years forever!
Aug 2002
Yeehaw, FL
16504_{8} Posts 

20060920, 01:32  #72 
"James Heinrich"
May 2004
exNorthern Ontario
3,361 Posts 
As drew said, the question then becomes how to figure out what qualifies as "tight", "decent" and "generous" memory amounts for a given exponent... Could you throw out a few numbers so that we can graph tight/decent/generous vs exponent, please?

20060920, 04:22  #73 
Oct 2004
Austria
2·17·73 Posts 

20060920, 13:17  #74  
P90 years forever!
Aug 2002
Yeehaw, FL
2^{2}×1,873 Posts 
Quote:
I suspect the "knee" is somewhere around 13 temporary variables. This lets prime95 run the 2*3*5 case in one pass over the 8 relative primes. So for a 2048K FFT you would need roughly 13 * 2048K * 8 (sizeof of a float) + 10M (rough guess of sin/cos and other needed data). That is 218MB. Do some real world tests to see if my suspicion is correct. 

20060920, 13:18  #75 
P90 years forever!
Aug 2002
Yeehaw, FL
2^{2}·1,873 Posts 

20061111, 20:30  #76 
"James Heinrich"
May 2004
exNorthern Ontario
3,361 Posts 
I've featurerequested this elsewhere before, but it may fit even better in with this multithreaded version:
Similar to the PauseWhileRunning setting, I'd like to see a LowMemoryUseWhileRunning setting which would limit Prime95 to only lowmemory tasks, such as P1.stage1, LL, TF. I find that Prime95's CPU usage is not an issue for me (idle priority seems to work very well), but the disk thrashing when loading up a memoryhogging program (Adobe*, games, etc) is unacceptable, and I need to either stop Prime95 completely or set the min/max memory settings to 8MB or somesuch to force Prime95 not to do any P1.stage2. 
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