Question Undervolting the CPU

Mellelmejor

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Jan 29, 2016
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I'm undervolting my I7 8750H and I'm a little bit confused about what's going on with my CPU and why. I have a Lenovo Legion Y730 17" and replaced the thermal paste of the CPU. I undervolted my latest stable undervolt was -235mv, the first and only crash was at -250mv.

I'm confused here because now even if I push the voltage to -350mv it doesn't crash and nothing really happens, sometimes even if I push the voltage lower, the power consumption goes up a little (61 instead of 58-57). My stock CPU package consumption was about 70W with clocks staying about 3.3 or even lower. After undervolting to -200mv I managed to have 3.9ghz on all cores and between 58 and 60W on the package.

Yesterday I was benchmarking at -235 and the clocks remained stable, literally a straight line, on 3.9, as well as the power on 59 and the voltage around 1v. Benchmarked for about half an hour with no problems and all the lines were totally straight, not even a slight fluctuation on the core.

I am benchmarking with p95, Aida and TS Bench all at the same time because p95 alone doesn't seem to push the CPU to its limits.

The problem being that as far as I know I would reach the limit once the CPU crashes (BSOD), but I'm not getting any, so I don't understand what is going on, as well as why it was so stable yesterday and now it is fluctuating between 50 and 60 (see screenshots).

The weirdest thing is that when is use TS Bench it is stable indeed, you can see the line to the left of the pictures, where it is quite stable at max clocks under 60W. After the TS Bench stops and p95 + Aida continue, I get this fluctuations which I wasn't getting yesterday with the same settings.

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Could someone explain to me what is going on in here, as well as why, and also why yesterday it was a straight line with the exact same settings, and how do I know when do I ACTUALLY reach my undervolting limit? Because I can seem to be able to push the voltage lower and lower, but nothing actually changes and I don't get a BSOD. Of course the actual voltages remain above .950 and under 1.050 usually, but even so I don't understand why is this like this.

These graphs are with -230mv, and as far as I can tell it is stable. My temps are always under 90 even with everything maxed out (the throttling you see there is just an outlier).

I understand the power limit of this CPU is 50W and it might be because of that, but doesn't explain why it was stable at 58W yesterday and no fluctuation, as well as why it isn't crashing or reducing the clocks (aside of the fluctuation).

PS: No, this is not my first time doing this. This is a new laptop to me and a much powerful now, so I am also dealing with different stuff here. I'm not that knowledgeable or experienced either, but I have an idea of what I'm doing.

Thanks a lot for your time!
 

Lutfij

Titan
Moderator
Are you on the latest BIOS for your laptop's motherboard? Often times with overclocking, stress testing doesn't always reveal an issue with your apparent mods, until you maybe fire up a game. It's also possible that one or more games will run fine with no issues while one or more games might not like what you've done.

I'm assuming you've used this guide in dealing with Intel's XTU app...?
 

Mellelmejor

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Jan 29, 2016
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Are you on the latest BIOS for your laptop's motherboard? Often times with overclocking, stress testing doesn't always reveal an issue with your apparent mods, until you maybe fire up a game. It's also possible that one or more games will run fine with no issues while one or more games might not like what you've done.

I'm assuming you've used this guide in dealing with Intel's XTU app...?

I'm using ThrottleStop. I am in the latest BIOS, and I'm not worried on whether my games will run or not, but rather I want to learn how to identify when I've reached my CPU limit and understand why it is behaving as it is.
 

Mellelmejor

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Jan 29, 2016
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ThrottleStop is a bad idea. It simply turns OFF the throttling of the CPU when it goes past its thermal threshold.
Thanks for your response, but this is not the kind of information I'm looking for. Throttlestop doesn't "unthrottle" the CPU if it the temperature is too high, I guess maybe if you turn off that option, but I didn't and I also do not have thermal issues, so that's not a problem.