Uneven core temps using Prime95

Nov 28, 2018
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So I was using cinebench and get fairly even temps on all cores with 6c difference between lowest and hottest core


But using Prime95 there was a difference up to 17c on two of the cores never seen anything like it before


This is a 9700k at 5ghz temps max 80c on prime 69c on cinebench

 

CompuTronix

Intel Master
Moderator
Just as it should be, and as expected.

ivandanko,

Sorry you missed the memo. Do not use Prime95 versions later than 26.6. Here's why:

Not all loads are created equal. “Stress” tests vary widely and can be characterized into two categories; stability tests which are fluctuating workloads, and thermal tests which are steady workloads. Intel tests their processors at a steady 100% TDP workload to validate Thermal Specifications.

Prime95 version 26.6 Small FFT's is ideal for CPU thermal testing, because it's a steady 100% workload with steady Core temperatures that typically runs Core i variants with Hyperthreading and Core 2 processors within +/- a few % of TDP. No other utility so closely replicates Intel's test conditions.

Utilities that don't overload or underload your processor will give you a valid thermal baseline. Here’s a comparison of utilities grouped as thermal and stability tests according to % of TDP, averaged across six processor Generations at stock settings rounded to the nearest 5%:

All tests will show 100% CPU Utilization in Windows Task Manager, which indicates processor resource activity, not % TDP workload. Core temperatures correspond directly to Power dissipation (Watts) which is workload. Prime95 v26.6 Small FFT’s provides a true and steady 100% workload, so if Core temperatures are below 85°C, then your processor should run the most demanding real-world workloads without overheating.

Each test creates distinct thermal signatures. Here's a few examples:

Shown above from left to right: Small FFT's, Blend, Linpack and IntelBurn Test.

Note the steady thermal signature of Small FFT's, which allows accurate measurements of Core temperatures. A steady 100% workload is key for thermal testing so the CPU, cooler, socket, motherboard and voltage regulators can thermally stabilize.

2nd and 3rd Generation i7, i5 and i3 CPU’s have AVX (Advanced Vector Extension) Instruction Sets. 4th through 9th Generation i9, i7, i5 and i3 CPU’s have AVX2 Instruction Sets. Prime95 versions later than 26.6 run AVX/2 code on the CPU's Floating Point Unit (FPU), which is an unrealistic workload. 2nd and 3rd Generation CPU’s are minimally affected by AVX, but 4th through 9th Generation with AVX2 may experience Core temperatures up to 20°C higher.

Many 6th through 9th Generation motherboards address the AVX problem by providing “offset” adjustments (downclock) in BIOS. -3 (300 MHz) or more may be needed to limit Core temperatures to 85°C. Since 4th and 5th Generation don’t have AVX offsets, you can create a BIOS Profile for gaming, and a downclock Profile for AVX apps such as rendering or transcoding. If you don’t use AVX apps, BIOS should still be configured for it, as certain utilities use AVX for stability testing.

AVX can be disabled in Prime95 versions later than 26.6 by inserting "CpuSupportsAVX=0" into the "local.txt" file in Prime95's folder. However, since Core temperatures will be the same as 26.6, it's easier to just use 26.6. AVX doesn't affect Core i 1st Generation, Core 2, Pentium or Celeron processors as they don't have AVX/2 Instruction Sets. As per Intel’s Datasheets, TDP and Thermal Specifications are validated “without AVX”.

• Prime95 v26.6 - http://www.mersenneforum.org/showthread.php?t=15504

There's a Sticky at the top of the CPU's Forum you need to read: Intel Temperature Guide - http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html

CT :sol:
 
Nov 28, 2018
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Doing a few more tests I'm getting mid high 70's on a few cores and 4 were in low 40s

This is using Prime 95s small FFTs test
 
It looks to be a little bit out of Intel specifications.
It could be that the version of Prime95 is not optimized for the 9 gen just yet. Try using version Prime95 26.6.

Also, Intel specifications allow for up to 10° C deviation from the highest and lowest core temps, since factors like Intel thermal solution application between the IHS and die could vary and the Digital Thermal Sensor (DTS) could be off by a few degrees.
If you see a 20° C deviation from the highest and lowest core temps then you should be concerned and it could be cause for a RMA.
 
Nov 28, 2018
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Ran some games and benchmarks even temps its just prime doing it though none of what I tested used as much cpu as prime

If something was wrong though wouldn't it show doing other things?
 
Nov 28, 2018
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29.4b8


I don't know other good free cpu tests I tried cinebench, aida64 extreme and 3dmark demo time spy all temps are fine.



 
Nov 28, 2018
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Ok I went back to default stock speed (4.8ghz on my motherboard because of the MCE)

Its giving normal even temps on cores


So it was the overclock that did it..


 

CompuTronix

Intel Master
Moderator
Just as it should be, and as expected.

ivandanko,

Sorry you missed the memo. Do not use Prime95 versions later than 26.6. Here's why:

Not all loads are created equal. “Stress” tests vary widely and can be characterized into two categories; stability tests which are fluctuating workloads, and thermal tests which are steady workloads. Intel tests their processors at a steady 100% TDP workload to validate Thermal Specifications.

Prime95 version 26.6 Small FFT's is ideal for CPU thermal testing, because it's a steady 100% workload with steady Core temperatures that typically runs Core i variants with Hyperthreading and Core 2 processors within +/- a few % of TDP. No other utility so closely replicates Intel's test conditions.

Utilities that don't overload or underload your processor will give you a valid thermal baseline. Here’s a comparison of utilities grouped as thermal and stability tests according to % of TDP, averaged across six processor Generations at stock settings rounded to the nearest 5%:

All tests will show 100% CPU Utilization in Windows Task Manager, which indicates processor resource activity, not % TDP workload. Core temperatures correspond directly to Power dissipation (Watts) which is workload. Prime95 v26.6 Small FFT’s provides a true and steady 100% workload, so if Core temperatures are below 85°C, then your processor should run the most demanding real-world workloads without overheating.

Each test creates distinct thermal signatures. Here's a few examples:

Shown above from left to right: Small FFT's, Blend, Linpack and IntelBurn Test.

Note the steady thermal signature of Small FFT's, which allows accurate measurements of Core temperatures. A steady 100% workload is key for thermal testing so the CPU, cooler, socket, motherboard and voltage regulators can thermally stabilize.

2nd and 3rd Generation i7, i5 and i3 CPU’s have AVX (Advanced Vector Extension) Instruction Sets. 4th through 9th Generation i9, i7, i5 and i3 CPU’s have AVX2 Instruction Sets. Prime95 versions later than 26.6 run AVX/2 code on the CPU's Floating Point Unit (FPU), which is an unrealistic workload. 2nd and 3rd Generation CPU’s are minimally affected by AVX, but 4th through 9th Generation with AVX2 may experience Core temperatures up to 20°C higher.

Many 6th through 9th Generation motherboards address the AVX problem by providing “offset” adjustments (downclock) in BIOS. -3 (300 MHz) or more may be needed to limit Core temperatures to 85°C. Since 4th and 5th Generation don’t have AVX offsets, you can create a BIOS Profile for gaming, and a downclock Profile for AVX apps such as rendering or transcoding. If you don’t use AVX apps, BIOS should still be configured for it, as certain utilities use AVX for stability testing.

AVX can be disabled in Prime95 versions later than 26.6 by inserting "CpuSupportsAVX=0" into the "local.txt" file in Prime95's folder. However, since Core temperatures will be the same as 26.6, it's easier to just use 26.6. AVX doesn't affect Core i 1st Generation, Core 2, Pentium or Celeron processors as they don't have AVX/2 Instruction Sets. As per Intel’s Datasheets, TDP and Thermal Specifications are validated “without AVX”.

• Prime95 v26.6 - http://www.mersenneforum.org/showthread.php?t=15504

There's a Sticky at the top of the CPU's Forum you need to read: Intel Temperature Guide - http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html

CT :sol:
 

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