i7-2600k on Windows 8.

[Flatlander]

Why does Prime95 choose 4 threads instead of 8?

Would switching to 64bit Windows give me a speed increase?

(I haven't used Prime95 in ages.)

[science_man_88]

Originally Posted by Flatlander

Would switching to 64bit Windows give me a speed increase?

from another thread:

Originally Posted by Prime95

BTW, if your CPU supports 64-bit then 64-bit prime95 is 10-15% faster than 32-bit prime95.

[Flatlander]

Thanks. I'll re-install tonight when everything hits 100%. I assume the save files won't transfer?
64bit will run hotter?
Should I force 8 threads?

[Dubslow]

The save files should transfer. The intermediate data is independent of calculation method.

[swl551]

Originally Posted by Flatlander

Why does Prime95 choose 4 threads instead of 8?

1. Hyperthreading is turned off in the bios.
2. P95 didn't detect all cpu configs.
3. you can manually set it to 8 from the menu.


Expect to see ~0.026 iteration times for 4 threads and ~0.050 for 8 threads as hyperthreading comes at a cost. (4.0 ghz, dual channel memory, LL testing).

Your mileage may vary a bit, but you'll see similar results.

[Flatlander]

Originally Posted by swl551

1. Hyperthreading is turned off in the bios.
2. P95 didn't detect all cpu configs.
3. you can manually set it to 8 from the menu.


Expect to see ~0.026 iteration times for 4 threads and ~0.50 for 8 threads as hyperthreading comes at a cost. (4.0 ghz, dual channel memory, LL testing).

Your mileage may vary a bit, but you'll see similar results.

I'm getting 0.030, about right.

[Main thread Feb 20 19:18] Mersenne number primality test program version 27.7
[Main thread Feb 20 19:18] Optimizing for CPU architecture: Core i3/i5/i7, L2 cache size: 256 KB, L3 cache size: 8 MB
[Main thread Feb 20 19:18] Logical CPUs 1,5 form one physical CPU.
[Main thread Feb 20 19:18] Logical CPUs 2,6 form one physical CPU.
[Main thread Feb 20 19:18] Logical CPUs 3,7 form one physical CPU.
[Main thread Feb 20 19:18] Logical CPUs 4,8 form one physical CPU.
[Main thread Feb 20 19:18] Starting workers.

Core(TM) i7-2600K CPU @ 3.40GHz
CPU speed 3392.28 MHz, 4 hyperthreaded cores
CPU features: Prefetch SSE, SSe2 SSe4, AVX
...

[swl551]

Originally Posted by Flatlander

I'm getting 0.030, about right.

Looks good. However you on version 27.7 and 27.9 is available. I have read posts where people stated better stability with hyperthreading using 27.9. I never had a problem with 27.7, but now run all my PCs on 27.9 anyway.

[kracker]

4. Hyper-threading makes it actually slower, at least for LL tests.

[Flatlander]

Thanks. Things are starting to make sense again.
But, what happened to P90 years!? (Or was it days?)

[Flatlander]

From the 'Best way to find large factors thread',

Originally Posted by ATH

P-1 will also run in around 1 day (anywhere from 12 hours to 2-3 days probably) depending on how much RAM you give it and how fast your CPU is.

It's almost a "waste" now to trialfactor on a CPU since GPU's are so much faster at it and P-1 is more needed atm, but it is of course up to you what you want to do.

For P-1 you should give at least 300 Mb RAM for every thread that runs P-1, and the more the better.

1) If I choose P-1 work should I run on 8 threads or 4?
(2560K of 4096K reserved 24/7, i7-2600k on 64bitWin8)

2) If 8 threads is faster is that enough memory? Candidates are at 62-63M.
Stage 1 of M62,089,483 says,

Using AVX FFT length 3360K, ...

Thanks.

[Dubslow]

Originally Posted by Flatlander

From the 'Best way to find large factors thread',

1) If I choose P-1 work should I run on 8 threads or 4?
(2560K of 4096K reserved 24/7, i7-2600k on 64bitWin8)

2) If 8 threads is faster is that enough memory? Candidates are at 62-63M.
Stage 1 of M62,089,483 says,

Thanks.

I would say 4 is probably better -- the more independent threads, the more memory bandwidth you need, and with AVX and DDR3-1333 you're pretty close the memory-bottlenecking limit as it is.

(Testing of course is the best way to produce an answer )