Prime95 version 25.5

[James Heinrich]

I'm still getting hard crashes of v25.5 on WinXP32 on my Northwood 3.0C. I ran a 2-thread torture test for 14 hours today, no problems at all, but tried running ECM in 2 threads for maybe 15 minutes and it died. No errors logged.

[StarQwest]

OK, I just increased my L2 cache to 32,768KB and the per iteration time decreased to 0.644 seconds. Is there still something I can do to reduce it to 0.500?

[ixfd64]

How do you modify the L2 cache size?

[Prime95]

Originally Posted by StarQwest

OK, I just increased my L2 cache to 32,768KB and the per iteration time decreased to 0.644 seconds. Is there still something I can do to reduce it to 0.500?

How can you increase your L2 cache? The L2 cache is part of your CPU.

Xyzzy's guess is probably accurate. Your huge FFT is putting enormous pressure on your smallish L2 cache. Using another CPU increases the pressure on the L2 cache - negating much of the advantage of using a second CPU.

What can you do? Not much short of buying new hardware. Sorry.

[Prime95]

Originally Posted by James Heinrich

I'm still getting hard crashes of v25.5 on WinXP32 on my Northwood 3.0C. I ran a 2-thread torture test for 14 hours today, no problems at all, but tried running ECM in 2 threads for maybe 15 minutes and it died. No errors logged.

Is it dying because of overcommitting memory? I have a fix for that particular bug. I've uploaded a new Win32 version for you to try.

[StarQwest]

Originally Posted by Prime95

How can you increase your L2 cache? The L2 cache is part of your CPU.

Xyzzy's guess is probably accurate. Your huge FFT is putting enormous pressure on your smallish L2 cache. Using another CPU increases the pressure on the L2 cache - negating much of the advantage of using a second CPU.

What can you do? Not much short of buying new hardware. Sorry.

It is easy to increase your cache. First press Ctrl+Alt+Delete to bring up Windows Task Manager (I am doing this on Windows XP, I don't know if this will work for Vista). Click on the performance tab and there will be a "Physical Memory (K)" section. Look at your System Cache to see how much cache you have available (it should be in the order of 400,000KB). Then, open up your Prime95 v.25.5 folder and click on local.txt. It will open up a configuration setting text box. Insert the line CpuL2CacheSize=32768. This will increase your L2 Cache to 32,768KB. You can set the number to anything you want up to your available cache limit.

I just increased the cache to 256,000KB and it reduced interation time to 0.636 seconds. However, I noticed that if I even move the mouse the iteration time increases to 0.650 - 0.660 seconds, even though I have the priority set to 10! Another thing that I am wondering about is that I only have 1GB of RAM on my computer. I am allotting 920MB (the maximum allowed) to this system, but Windows Task Manager says Prime95 is only using 367MB (it uses about 20MB for a 10 million digit number) and 95% of the CPU. Would adding more RAM increase the speed at all, or is 0.636 iterations per second the best I can do with my current machine using both cores of the Pentium D?

[petrw1]

Originally Posted by StarQwest

I just increased the cache to 256,000KB and it reduced interation time to 0.636 seconds.

Is this just a version 25 thing?

I am still running the current production version 24.14 and LL testing a number in the 36M range. I tried CPUL2CACHESIZE anywhere from 128 to 32768 and the per iteration time on my P4 2.4 Ghz was always 0.082 secs.

[StarQwest]

Originally Posted by petrw1

Is this just a version 25 thing?

I am still running the current production version 24.14 and LL testing a number in the 36M range. I tried CPUL2CACHESIZE anywhere from 128 to 32768 and the per iteration time on my P4 2.4 Ghz was always 0.082 secs.

It doesn't improve your per iteration time all that much (increasing from 128MB to 256000MB improved mine from 0.660 seconds to 0.636 seconds). The only way to check if it worked or not is to open up Prime95, click on Options, then CPU. It will tell you your L2 Cache size in this window at the bottom.

[chappjc]

Originally Posted by StarQwest

It is easy to increase your cache. First press Ctrl+Alt+Delete to bring up Windows Task Manager (I am doing this on Windows XP, I don't know if this will work for Vista). Click on the performance tab and there will be a "Physical Memory (K)" section. Look at your System Cache to see how much cache you have available (it should be in the order of 400,000KB). Then, open up your Prime95 v.25.5 folder and click on local.txt. It will open up a configuration setting text box. Insert the line CpuL2CacheSize=32768. This will increase your L2 Cache to 32,768KB. You can set the number to anything you want up to your available cache limit.

L2 cache is something completely different from the Physical Memory you are describing.

[Mr. P-1]

Originally Posted by StarQwest

It is easy to increase your cache. First press Ctrl+Alt+Delete to bring up Windows Task Manager (I am doing this on Windows XP, I don't know if this will work for Vista). Click on the performance tab and there will be a "Physical Memory (K)" section. Look at your System Cache to see how much cache you have available (it should be in the order of 400,000KB). Then, open up your Prime95 v.25.5 folder and click on local.txt. It will open up a configuration setting text box. Insert the line CpuL2CacheSize=32768. This will increase your L2 Cache to 32,768KB. You can set the number to anything you want up to your available cache limit.

As has already been pointed out, the system cache and the L2 cache are two very different things. You cannot alter your L2 cache other than by changing your processor. What you are doing with your CpuL2CacheSize line is overriding Prime95's auto-detected value.

I just increased the cache to 256,000KB and it reduced interation time to 0.636 seconds.

That's very interesting, since it indicates, at least for these huge exponents, that the codepaths used when the autodetected (i.e., correct) value is used are highly suboptimal. George might want to have a look at that, (or he might not, given that the exponent is so far from the normal range).

However, I noticed that if I even move the mouse the iteration time increases to 0.650 - 0.660 seconds, even though I have the priority set to 10! Another thing that I am wondering about is that I only have 1GB of RAM on my computer. I am allotting 920MB (the maximum allowed) to this system, but Windows Task Manager says Prime95 is only using 367MB (it uses about 20MB for a 10 million digit number)

That sounds about right. Extra memory is only used during stage 2 of P-1 and ECM.

Incidently, have you tried running a few ECM curves on your exponent? It could find a factor missed by P-1 and trial factoring and save you a lot of time.

EDIT: the limit for ECM factoring is 20,500,000, which your exponent is obviously way beyond.

and 95% of the CPU.

My guess is that LL iterations can't be parallelised 100%, so for part of the time one thread will be waiting for the other.

Would adding more RAM increase the speed at all, or is 0.636 iterations per second the best I can do with my current machine using both cores of the Pentium D?

Extra ram won't help but further revisions of the code might.

[ixfd64]

Yes, the L2 cache and physical memory are two different things. I tried increasing my "L2 cache" to 32,768 kb like you described, and nothing happened.