i5 8250u randomly capping itself at 15-16w despite no thermal throttling.

[LainIwakura]

Even with PL1 and PL2 set to 4095, it would go up to 20-35w sometimes then after some time, despite no thermal throttling, power throttle down to 15-16 watts. Any clue what this could be? The laptop model is an

HP Pavilion x360 - 14-cd0001nx, running Windows 10​

 

[unclewebb]

The 8250U has a 15W TDP rating.

Intel® Core™ i5-8250U Processor (6M Cache, up to 3.40 GHz) Product Specifications

Intel® Core™ i5-8250U Processor (6M Cache, up to 3.40 GHz) quick reference guide including specifications, features, pricing, compatibility, design documentation, ordering codes, spec codes and more.

ark.intel.com

HP is likely using an embedded controller (EC) to enforce this 15W limit. When the EC turbo power limits are set lower than the MSR or MMIO power limits, during a long term stress test, the CPU will be limited to whatever value the EC has set. The lowest set value wins control of the CPU.

Not all manufacturers use an EC to enforce power limits. I had a Lenovo C930 laptop with a similar 8550U CPU and it was possible to run it well beyond the 15W TDP spec indefinitely. It would start to thermal throttle at 95°C but there was no power limit throttling.

Now you know what to test the next time you buy a laptop. Performance of the exact same CPU can vary significantly depending on what limits a manufacturer has set.

 

[LainIwakura]

The 8250U has a 15W TDP rating.

Intel® Core™ i5-8250U Processor (6M Cache, up to 3.40 GHz) Product Specifications

Intel® Core™ i5-8250U Processor (6M Cache, up to 3.40 GHz) quick reference guide including specifications, features, pricing, compatibility, design documentation, ordering codes, spec codes and more.

ark.intel.com

HP is likely using an embedded controller (EC) to enforce this 15W limit. When the EC turbo power limits are set lower than the MSR or MMIO power limits, during a long term stress test, the CPU will be limited to whatever value the EC has set. The lowest set value wins control of the CPU.

Not all manufacturers use an EC to enforce power limits. I had a Lenovo C930 laptop with a similar 8550U CPU and it was possible to run it well beyond the 15W TDP spec indefinitely. It would start to thermal throttle at 95°C but there was no power limit throttling.

Now you know what to test the next time you buy a laptop. Performance of the exact same CPU can vary significantly depending on what limits a manufacturer has set.

Would there be any way to override EC values, perhaps a BIOS mod or something physical?

 

[unclewebb]

Modifying the IMON Slope or IMON Offset BIOS variables can be used to trick the CPU into reporting power consumption incorrectly. Not sure if this would be possible on an HP laptop. I think the HP BIOS might be well protected.

 

[LainIwakura]

Modifying the IMON Slope or IMON Offset BIOS variables can be used to trick the CPU into reporting power consumption incorrectly. Not sure if this would be possible on an HP laptop. I think the HP BIOS might be well protected.

Well I am certainly willing to try.. are there any available BIOS mods for my model or a similar one? If there aren't, I'd like to know where I could go to attempt to create my own.

 

[unclewebb]

You will have to do some Google searching. I am not familiar with your laptop model or with any BIOS mod tools.

Maybe you can find some info on this site.

BIOS Modding Guides and Problems

about AMI and Phoenix/Award BIOSes

winraid.level1techs.com