cpu usage under 100%

jiangv · 2019-07-22, 04:21

Hi guys

when I using my computer running p95 stress testing, some of my cpu cores are not fully loaded, the usage jumping between 100% and 20%, but there is no error shows up, so what is this situation means, my pc have flaws?

Thanks in advance! :D

VBCurtis · 2019-07-22, 04:24

Do you know what hyperthreads are? What model CPU do you have? What operating system?
Prime95 usually uses as many threads as there are actual cores. Windows doesn't know the difference between actual cores and hyperthreads, so a 4-core CPU may show up in windows as an 8-core if hyperthreading is enabled. Prime95 will use all 4 cores, but windows shows half the chip as unused; it's a flaw in Windows' presentation.
If you don't have hyperthreading, then it's something else...

jiangv · 2019-07-22, 05:40

Thanks VBCurtis

I using I9 9900X doing overclocking, 10 cores running at 4.9Ghz, with non-avx and HT disable, so in system it have 10 cores and 10 threads, Prime running 10 threads.

Uncwilly · 2019-07-22, 06:06

How are your temps?

What is your RAM set-up?

jiangv · 2019-07-22, 06:10

Thanks Uncwilly

I have 4x8G gskill ddr4 3200c14 mems using xmp profile which is MB certified. cpu cache ratio is 2.7G.

Prime95 · 2019-07-22, 06:14

It in no way indicates a PC flaw. It is possible you are thrashing.

Try reducing the amount of RAM prime95 is allowed to use (a custom torture test). Or do an in-place torture test.

jiangv · 2019-07-22, 06:16

Thanks Prime95

I will try this way and reply you soon, hope it could resolve my problem, :D

jiangv · 2019-07-23, 09:44

Hi Prime95

I just reset my system config to default except disabled HT.

my set-up is a 9900X cpu, x299 MB, 16GB ddr4 mem running in default at all. no overclocking at all.

I was running Prime95 298B5 version, section 1, smallest fft testing without avx instructions.
using hwinfo64 to monitor the system status, no other app running at the time

at the first it looks good, but after about ten mins, it start drop, the avg usage for some cores were only 80% to 90%, and the real time usage not always in 100%, also the same when I check windows task manager. and there is no any error shows up in the p95 thread output, system temp also in a good status, maximum temp under 60.

so, do you know what happening exactly?

Prime95 · 2019-07-23, 16:53

I don't have a Windows machine, so I do not know what is happening. Maybe someone else here can help.

Rest assured, your machine is fine. Only be concerned if you see error messages in the worker windows.

kriesel · 2019-07-23, 18:36

Look for paging activity. Setting too large an allowed memory in prime95 can cause lots of paging to disk and back, and reduced cpu usage. Some web browsers can grow to multi-gigabyte working sets and cause the problem also.

Check for other tasks that run. I've found that using one core on another task such as the gcd phase of CUDAPm1, on a system without hyperthreading, shuts down an entire prime95 worker for the duration, so if that worker is assigned n cores, n-1 go idle.
Probably other applications, or system tasks could have that effect too; file indexing, disk defragmentation, backups, virus scans, etc.

jiangv · 2019-07-25, 01:38

Thanks Prime95

yes I am taking it as a good sign as long as I dont see errors.

another question about the new version Prime95, I saw when I disable avx by modify local.txt with cpusupportavx=0, it only have fft length 4k/5k/6k available for testing, can't test mem as the old version, so how can I using non-avx instructions to test mem with new Prime95.

Thanks.

2019-07-22, 04:21	#1
jiangv Jul 2019 F₁₆ Posts	cpu usage under 100% Hi guys when I using my computer running p95 stress testing, some of my cpu cores are not fully loaded, the usage jumping between 100% and 20%, but there is no error shows up, so what is this situation means, my pc have flaws? Thanks in advance! :D

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2019-07-22, 04:24	#2
VBCurtis "Curtis" Feb 2005 Riverside, CA 2·2,927 Posts	Do you know what hyperthreads are? What model CPU do you have? What operating system? Prime95 usually uses as many threads as there are actual cores. Windows doesn't know the difference between actual cores and hyperthreads, so a 4-core CPU may show up in windows as an 8-core if hyperthreading is enabled. Prime95 will use all 4 cores, but windows shows half the chip as unused; it's a flaw in Windows' presentation. If you don't have hyperthreading, then it's something else...

2019-07-22, 05:40	#3
jiangv Jul 2019 1111₂ Posts	Thanks VBCurtis I using I9 9900X doing overclocking, 10 cores running at 4.9Ghz, with non-avx and HT disable, so in system it have 10 cores and 10 threads, Prime running 10 threads.

2019-07-22, 06:06	#4
Uncwilly 6809 > 6502 """"""""""""""""""" Aug 2003 101×103 Posts 2²·2,767 Posts	How are your temps? What is your RAM set-up?

2019-07-22, 06:10	#5
jiangv Jul 2019 F₁₆ Posts	Thanks Uncwilly I have 4x8G gskill ddr4 3200c14 mems using xmp profile which is MB certified. cpu cache ratio is 2.7G.

2019-07-22, 06:14	#6
Prime95 P90 years forever! Aug 2002 Yeehaw, FL 17×487 Posts	It in no way indicates a PC flaw. It is possible you are thrashing. Try reducing the amount of RAM prime95 is allowed to use (a custom torture test). Or do an in-place torture test.

2019-07-22, 06:16	#7
jiangv Jul 2019 17₈ Posts	Thanks Prime95 I will try this way and reply you soon, hope it could resolve my problem, :D

2019-07-23, 09:44	#8
jiangv Jul 2019 3×5 Posts	Hi Prime95 I just reset my system config to default except disabled HT. my set-up is a 9900X cpu, x299 MB, 16GB ddr4 mem running in default at all. no overclocking at all. I was running Prime95 298B5 version, section 1, smallest fft testing without avx instructions. using hwinfo64 to monitor the system status, no other app running at the time at the first it looks good, but after about ten mins, it start drop, the avg usage for some cores were only 80% to 90%, and the real time usage not always in 100%, also the same when I check windows task manager. and there is no any error shows up in the p95 thread output, system temp also in a good status, maximum temp under 60. so, do you know what happening exactly?

2019-07-23, 16:53	#9
Prime95 P90 years forever! Aug 2002 Yeehaw, FL 17·487 Posts	I don't have a Windows machine, so I do not know what is happening. Maybe someone else here can help. Rest assured, your machine is fine. Only be concerned if you see error messages in the worker windows.

2019-07-23, 18:36	#10
kriesel "TF79LL86GIMPS96gpu17" Mar 2017 US midwest 17220₈ Posts	Look for paging activity. Setting too large an allowed memory in prime95 can cause lots of paging to disk and back, and reduced cpu usage. Some web browsers can grow to multi-gigabyte working sets and cause the problem also. Check for other tasks that run. I've found that using one core on another task such as the gcd phase of CUDAPm1, on a system without hyperthreading, shuts down an entire prime95 worker for the duration, so if that worker is assigned n cores, n-1 go idle. Probably other applications, or system tasks could have that effect too; file indexing, disk defragmentation, backups, virus scans, etc.

2019-07-25, 01:38	#11
jiangv Jul 2019 3·5 Posts	Thanks Prime95 yes I am taking it as a good sign as long as I dont see errors. another question about the new version Prime95, I saw when I disable avx by modify local.txt with cpusupportavx=0, it only have fft length 4k/5k/6k available for testing, can't test mem as the old version, so how can I using non-avx instructions to test mem with new Prime95. Thanks.