Undervolting Dell laptops with Intel CPUs: Picking the right ones on the used market

[misha1350]

Hello! Recently I got myself a retired Dell Precision 3530 with an Intel Core i7-8750H (which is essentially Latitude 5591 with a dGPU) at my company. Thanks to them disabling the BIOS updates in their Windows 10 Enterprise, it was preserved with an old BIOS up until I bought it. I was able to undervolt rather well, and overall I got a great machine for its price - but I made a rookie mistake:

1. I didn't read if BIOS downgrading was possible, or necessary, for undervolting to work;
2. I didn't turn off UEFI Capsule Updates in the Dell BIOS;
3. I let Windows update my drivers automatically.
4. ??????
5. -15-20% performance, quietness and battery life loss in an instant!

I naively thought that Dell was not an empire of evil, unlike Lenovo's ThinkPad division, because I was not only able to downgrade the BIOS on my ThinkPad T480 from the newest ver. 1.51 to 1.26 (the last one before the dreaded microcode update) without issues, but I didn't need to - since the newest ThinkPad T480 BIOS still let me undervolt.

Apparently, Dell blocks BIOS downgrades outright if it has "critical security updates", which, judging by the amount of angry people who reported more heat, noise and outrageous idle power consumption, I assume, is a codeword for "critical planned obsolescence shenanigans". The last BIOS version for Latitude 5591 and Precision 3530 that supports undervolting is 1.10, which came out in September 2019 (before roughly November 2019 when they started locking it down). I am currently at 1.33 and I can only downgrade to 1.30

I decided that I would try my luck at the next trading window and I found an even more fantastic deal for me - a Latitude 5501 with an i7-9850H. I don't need a dGPU because I don't game and hardly ever use NVENC for anything (Intel QSV is great enough), but a fast CPU and better battery life due to no dGPU are much needed. The hardware layout seems worse, though, and the 97Wh batteries are not as easy to find as the Precision 3530's 92Wh was, but the CPU makes it worth buying for the $150 it sells for in my country. They seem to have a BIOS version 1.3.2 dating back to August 2019, and the later BIOS versions only came out later. So since the 9th gen CPUs appear to support undervolting too, is this laptop guaranteed to support undervolting?

 

[unclewebb]

is this laptop guaranteed to support undervolting?

When it comes to laptops and undervolting, I would not guarantee anything. Even if you get lucky and undervolting works, you might run into severe power limit throttling which is another Dell feature. I have seen some Dell laptops with 45W TDP CPUs that are forced to throttle along at 10W or less.

I would not buy an 8th or 9th Gen Dell laptop unless I could immediately return it with no questions asked. Even then I would be hesitant. Too many severe throttling problems can start out of nowhere and many of these problems cannot be fixed. Good luck.

 

[misha1350]

Even if you get lucky and undervolting works, you might run into severe power limit throttling which is another Dell feature. I have seen some Dell laptops with 45W TDP CPUs that are forced to throttle along at 10W or less.

I would not buy an 8th or 9th Gen Dell laptop unless I could immediately return it with no questions asked. Even then I would be hesitant. Too many severe throttling problems can start out of nowhere and many of these problems cannot be fixed. Good luck.

I shall then test the throttling in CPU benchmark and videogames, right? Since I have this laptop with surprisingly good build quality and hardly any heat from the keyboard (which is great for us programmers), I would like to see how well it would handle a sustained workload at 35W (which these CPUs seem to be rated for, especially because they only have one fan with two heatpipes). The VRMs on this model are not connected to the heatsink, so I am pretty interested in how well my Precision 3530 that I got for a low price ($220 for a model with i7-8750H, Quadro P600 4GB 25W (also non-undervoltable, sadly), and 32/512GB) handles the job. I will report on how hard it throttles under load later on.