i7-2600k on Windows 8.
 

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.)

:smile:

[QUOTE=Flatlander;330363]Would switching to 64bit Windows give me a speed increase?
[/QUOTE]

from another thread:
[QUOTE=Prime95;329612]BTW, if your CPU supports 64-bit then 64-bit prime95 is 10-15% faster than 32-bit prime95.[/QUOTE]

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?

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

[QUOTE=Flatlander;330363]Why does Prime95 choose 4 threads instead of 8?


:smile:[/QUOTE]

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.

[QUOTE=swl551;330380]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.[/QUOTE]
I'm getting 0.030, about right.
[QUOTE][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.
[/QUOTE]

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

[QUOTE=Flatlander;330383]I'm getting 0.030, about right.[/QUOTE]

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.

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

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

From the 'Best way to find large factors thread',
[QUOTE=ATH;329650]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.[/QUOTE]
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,
[QUOTE]Using AVX FFT length 3360K, ...[/QUOTE]
Thanks. :smile:

[QUOTE=Flatlander;330823]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. :smile:[/QUOTE]

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 :smile:)

[QUOTE=Flatlander;330823]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. :smile:[/QUOTE]
My evaluation of 8 threads on P-1 testing showed the same linear degradation in throughput as seen on LL tests. You are just weighing time vs concurrency. Personally I only run 4 threads on my i7 cuz it kills me to see my i5 based PCs kicking butt on my i7. An i7 with hyper-threading off is basically an i5 with more L1/L2 cache.