LL tests running at different speeds

[GARYP166]

I upgraded my PC last week. Prime 95 seems to have detected this, because I am now testing two numbers. But they never run at the same speed.

I then tried to copy and paste from the screen displays, and found that I have to copy by hand.

[Jun 29 18:17] Iteration 30130000 / 40962983 [73.55%] Per iteration time 0.158 sec
[Jun 29 18:36] Iteration 30140000 / 40962983 [73.57%] Per iteration time 0.113 sec
[Jun 29 19:00] Iteration 30150000 / 40962983 [73.60%] Per iteration time 0.140 sec
[Jun 29 20:46] Iteration 30160000 / 40962983 [73.62%] Per iteration time 0.491 sec
[Jun 29 21:08] Iteration 30170000 / 40962983 [73.65%] Per iteration time 0.129 sec

[Jun 29 18:03] Iteration 2730000 / 39815987 [6.85%] Per iteration time 0.110 sec
[Jun 29 18:24] Iteration 2740000 / 39815987 [6.88%] Per iteration time 0.122 sec
[Jun 29 18:50] Iteration 2750000 / 39815987 [6.90%] Per iteration time 0.159 sec
[Jun 29 19:13] Iteration 2760000 / 39815987 [6.93%] Per iteration time 0.137 sec
[Jun 29 19:28] Iteration 2770000 / 39815987 [6.95%] Per iteration time 0.088 sec

I am happy with the program speeding up or slowing down depending on what else I am doing, but why are the two primes not keeping in step with each other?

Gary

[cheesehead]

Originally Posted by GARYP166

I am happy with the program speeding up or slowing down depending on what else I am doing, but why are the two primes not keeping in step with each other?

The two exponents' tests are running in different cores. The "what else [you are] doing" runs on various cores at various times, so there's no lock-step.

Suppose 40962983 is being tested on core 0 and 39815987 is being tested on core 1.

Then when you start up Windows Explorer, for example, the OS may schedule it to run on core 0. Core 1 would be unaffected and the 39815987 test will proceed at the same speed as before, but the prime95 test of 40962983 on core 0 will be slowed down by interruptions for the higher-priority time slices given to Windows Explorer on that core.

[GARYP166]

Thanks

[TimSorbet]

Try finding the times they get when nothing else is using the CPU. Set the "Iterations between screen outputs" (in Options > Preferences) to something low like 10. Bring up Task Manager to check that Prime95 is getting all of your CPU. If they're about the same when it's like that, then it is just that other tasks get sent to one core more than the other. If not, then something else is going on. Either way, you can set that number back to 10000 so it doesn't flood your screen all the time.
Are the two numbers using the same FFT length? It says the FFT length used when you start/resume the number, e.g. "Resuming primality test of M40962983 using FFT length 2560K". Your two candidates are near an FFT cutoff. I don't think they should be using different FFT sizes unless your CPU doesn't support SSE2, in which case it wouldn't have two cores in the first place. (if this doesn't make sense, don't worry about it, just post those FFT size numbers from Prime95 )
Do you know if your CPU has two separate cores or if it is hyperthreaded? It might be related to that.

[starrynte]

Also, go to Edit -> Copy Window to copy the text from whichever window is selected at the time.

[henryzz]

in general i find on windows that a low priority job running on core 0 will lose more time than any other core

[cheesehead]

Originally Posted by henryzz

in general i find on windows that a low priority job running on core 0 will lose more time than any other core

I agree.

[Uncwilly]

Originally Posted by henryzz

in general i find on windows that a low priority job running on core 0 will lose more time than any other core

There are times that I do things that tie up a core with a browser. Core 1 is the one that suffers, it can virtually stop dead, while core 0 pumps right along.

[henryzz]

Originally Posted by Uncwilly

There are times that I do things that tie up a core with a browser. Core 1 is the one that suffers, it can virtually stop dead, while core 0 pumps right along.

weird
i must point out that i have found this with a quad not a duo

[GARYP166]

Originally Posted by Mini-Geek

Are the two numbers using the same FFT length? It says the FFT length used when you start/resume the number, e.g. "Resuming primality test of M40962983 using FFT length 2560K". Your two candidates are near an FFT cutoff.

Both are using FFT length 2560K.

Originally Posted by Mini-Geek

Do you know if your CPU has two separate cores or if it is hyperthreaded? It might be related to that.

No I'm afraid I don't know that. How would I find out please?

Gary

[patrik]

Originally Posted by GARYP166

[---]

No I'm afraid I don't know that. How would I find out please?

Gary

If you are using Windows and Intel, you can download the Intel® Processor Identification Utility. Install it, and then select the CPU Technologies tab.