CPU won't reach Max Turbo Frequency in Prime 95 (Temp: ~70, and fan speed is medium)

[inteli7.Ti]

Decided to undervolt an i5-8250u (Dell XPS 9370) using Throttlestop. I undervolted it 100mv, and then I ran prime 95. Before I ran prime 95, the cpu was running at 3.4 GHz (max turbo) but immediately after I started running prime 95, it went down to about 2.4 GHz. I don't think its because of the temperature, because the CPU package temperature is around 70 C. And, fan speed is medium (I've heard it go way louder). 

 

Any reason why this may be happening? Anything related with Speed Shift (Dell did disable speed shift on previous XPS laptops) or does Dell just want to be really, really safe?

[badreg]

It's probably power throttling. Does it start out at full turbo, and then throttle clocks after a few seconds?

 

Check with XTU to confirm.

[inteli7.Ti]

1 minute ago, starcoaster said:

have you considered this could be an AVX offset

I haven't thought about that, could be why. Is there a specific program(throttlestop??) or do I go into the BIOS to change the offset?

[inteli7.Ti]

2 minutes ago, badreg said:

It's probably power throttling. Does it start out at full turbo, and then throttle clocks after a few seconds?

 

 Check with XTU to confirm.

I'm charging it right now, and at idle it's running at 3.4 GHz. But it changes immediately after I start running prime95. 

 

I don't think its power throttling because its using 22-23 watts during prime95.

[unclewebb]

3 hours ago, inteli7.Ti said:

I don't think its power throttling

The Core i5-8250U has a TDP rating of 15 Watts so long term, they are designed to throttle down to this level.  Does ThrottleStop Limit Reasons not show you something glowing in red.  This is your reason for throttling.

[inteli7.Ti]

On 7/16/2019 at 7:04 PM, unclewebb said:

The Core i5-8250U has a TDP rating of 15 Watts so long term, they are designed to throttle down to this level.  Does ThrottleStop Limit Reasons not show you something glowing in red.  This is your reason for throttling.

Thanks for your reply! I did open Limit Reasons when running prime95 again, and sure enough there is something glowing red!

 

I read some other threads on this forum, and is it right that the PL1 and PL2 limits cannot be changed? I'm just wondering if I get it to stop throttling.

 

[unclewebb]

Most manufacturers that are using low power U series CPUs set the PL1 throttling limit equal to the rated TDP which is 15 Watts.  Some manufacturers will allow you to use software to increase this limit while many Dell laptops do not allow this.

There are actually a primary and a secondary set of power limits.  Download the RwDrv.zip file from Mega and copy the RwDrv.sys file into your ThrottleStop folder.

https://mega.nz/#!CNNA0SoC!Z2Xi2icwX4d4jzW016dKnKGhVglWmSSPpgiRU7VCG6g

 

Now you can open up the FIVR window and check the Disable and Lock Turbo Power Limits option.  Close the FIVR window, open the TPL window and try increasing your Turbo Boost Long and Short power limits beyond 15 Watts.  With my Lenovo laptop, the sky is the limit.