Question Regarding Power Limit Throttling

[Muhlis]

 

Hi,

 

I have a laptop with i5-8250U. Recently, I tried out the Intel XTU software to undervolting my laptop. At first, I ran a stress test on my CPU and noticed it score a 2.84 GHz maximum "max core frequency" and 64°C maximum package temperature.

 

Then, I tried -0,080 V (undervolting). I ran a stress test again and it scored a 3.03 GHz maximum "max core frequency" (the average is much higher now) and the same maximum package temperature.

 

But it still can't reach 3.4 GHz on 100% CPU utilization. I also notice that power limit throttling is on when frequencies drop. (In the picture; green is before undervolting and yellow is after undervolting)

 

Can you guys help me with this?

 

Thanks.

[unclewebb]

 

2 hours ago, Muhlis Gursoy said:

I ran a stress test on my CPU

What stress test?

 

The 8250U has a 15 Watt TDP limit.  During any long term test, by default, Intel designed this CPU to throttle based on this 15 Watt TDP power limit.  That is what Intel XTU is telling you.

 

Do you have access to the two turbo power limits in XTU and have you tried increasing those?  If you raise the short and long power limits, then your CPU might be able to run for a longer period of time or even indefinitely without any power limit throttling problems.

[Muhlis]

10 hours ago, unclewebb said:

What stress test?

When I wrote this answer, I was using XTU's native stress test. Then I tried Prime95 overnight and made sure -0,090 V is working well.

 

I think I have access to them (I included a picture below this). How much should I increase it? In another post, I read that I should increase it to the maximum (unlimited) but I was doubting, will it harm my laptop?

[unclewebb]

Intel's low power U series CPUs are not intended to be used to run stress tests like Prime95 or the XTU stress test at full speed.  It has a 15 Watt TDP rating.  To keep power consumption at that level during one of these tests, the CPU is designed to throttle back its speed and slow down.  

8 hours ago, Muhlis Gursoy said:

will it harm my laptop

Probably not but it might.  If you are worried about hurting your laptop then do not run Prime95 overnight.  If you want some more performance, try increasing the turbo power limits.  Instead of 15 Watts, try using 20 Watts or 25 Watts.  Watch your CPU temperature.  As long as your CPU heatsink and fan are up to the task and your CPU is not overheating, everything should be OK.

 

Some laptops with low power U series CPUs have a hard 15 Watt power limit set internally.  Adjusting the turbo power limits that Intel XTU lets you adjust might not get you beyond 15 Watts.  It never hurts to try.  Lenovo left my 8th Gen U series CPU unlocked so it has no problem running way beyond its 15 Watt power limit indefinitely or until it overheats.

 

https://i.imgur.com/eo0J744.png

[Muhlis]

54 minutes ago, unclewebb said:

Some laptops with low power U series CPUs have a hard 15 Watt power limit set internally.

I think my laptop has that limit. I noticed every time the power limit throttling on (when 100% utilization), the package TDP drops to 10W (max 13W). The temperature average didn't change more than 2-3°C.

 

I increased the turbo boost limits to 25W, btw I equalized both turbo boost power max and turbo boost short power max. Seems like the frequency increased by 5%? Whatever, the undervolted CPU still better than the default one.

[svmlegacy]

On 3/28/2020 at 12:37 PM, Muhlis Gursoy said:

Hi,

 

I have a laptop with i5-8250U. Recently, I tried out the Intel XTU software to undervolting my laptop. At first, I ran a stress test on my CPU and noticed it score a 2.84 GHz maximum "max core frequency" and 64°C maximum package temperature.

 

Then, I tried -0,080 V (undervolting). I ran a stress test again and it scored a 3.03 GHz maximum "max core frequency" (the average is much higher now) and the same maximum package temperature.

 

But it still can't reach 3.4 GHz on 100% CPU utilization. I also notice that power limit throttling is on when frequencies drop. (In the picture; green is before undervolting and yellow is after undervolting)

 

Can you guys help me with this?

 

Thanks.

Intel TurboBoost is really what makes these low power CPU's viable. 3.4 GHz is the maximum it's allowed to hit for a single core load. For a U class CPU, typically Intel drops the maximum speed for all-core significantly. The reason for this is simple: 2 cores at the same speed draw double the power as a single. If you're not using all cores, there's additional power headroom to let a single core clock higher. If you really want to see it hit 3.4, boot up Windows with 1 thread, to force it into a single core scenario, and run your benchmark.

[unclewebb]

@svmlegacy  Many Intel CPUs use staggered turbo ratios depending on how many cores are active.  The 8250U is different.  It can use the full 34 multiplier whether 1, 2, 3 or all 4 cores are active.  Intel relies on reduced power limits to control these CPUs and leaves the turbo ratios untouched.

5 hours ago, Muhlis Gursoy said:

I think my laptop has that limit.

What laptop model do you have?  Dell and HP firmly lock most of their low power U series laptops but Lenovo and some other manufacturers leave the maximum power limits completely unlocked.  Intel XTU is not capable of taking advantage of this situation.  If you want to try running at a higher power limit, you will need to switch from XTU to ThrottleStop.  It has a feature in its FIVR window called Disable and Lock Turbo Power Limits.  This has made a huge difference to many laptops.

[Muhlis]

13 hours ago, unclewebb said:

What laptop model do you have?  Dell and HP firmly lock most of their low power U series laptops but Lenovo and some other manufacturers leave the maximum power limits completely unlocked.  Intel XTU is not capable of taking advantage of this situation. 

I use Acer Swift 3 (SF315-52G). Also the latest XTU version wasn't working with my laptop, I downloaded a previous version that was provided from someone in Acer community. I have tried the ThrottleStop but didn't understand the process much, but I still have it installed on my laptop.