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Old 2016-01-28, 17:13   #1
lidocorc's Avatar
Nov 2008
Rosenheim, Germany

110002 Posts
Default Unable to detect logical CPUs

I changed the processor in my computer, now it's a i7-3820, which is a model with hyperthreaded logical CPUs. When I run prime95 on that processor I get the message: "Unable to detect one of the hyperthreaded logical CPUs." Is this important or is it to be ignored? Will my computer be more effective if it uses all 8 logical CPUs? And if yes, what can I try to get this working?

Thanks for help
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Old 2016-01-28, 23:46   #2
VBCurtis's Avatar
Feb 2005
Riverside, CA

495510 Posts

For LL testing, hyperthreads are not effective; P95 tries to detect hyperthreaded cores in order to avoid using them.
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Old 2016-01-29, 01:58   #3
Romulan Interpreter
LaurV's Avatar
Jun 2011

3·3,253 Posts

Read in the docs (and undoc.txt) and search the forum about affinity scramble. Use the right affinity (if it is not detected properly) and do not use more threads (workers times threads per worker) than the physical cores of the CPU, unless you do ECM or P-1, both of them benefit a bit from HT in their "stage 1" phases. For LL tests, HT is detrimental.

Last fiddled with by LaurV on 2016-01-29 at 02:00
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Old 2016-07-16, 04:38   #4
Jul 2016

1 Posts
Default Same problem

Hello. I am new to the forum and I just started running Prime95. I am also having the same issue with a message in the communications window that it is unable to detect logical CPUs. I am also getting a message in the worker window that says possible hardware errors may have occurred. I am using an Intel 5820k CPU, Asus Rampage V Extreme MB, Corsair H110i cpu water cooler, 64 gb RAM, and Asus Strix 980Ti GPU. I have checked on my logical cpu pairings and have used AffinityScramble2=0123456789AB. Please tell me if this is the correct annotation or if I need to change it or if there is anything else I should do to get rid of these errors or if it's negligible. Thank you!!!
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