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Undervolted my Skylake CPU-so far, so good!

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Stevo
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Undervolted my Skylake CPU-so far, so good!

#1 Post by Stevo » Tue May 08, 2018 3:32 pm

This works with a p-state kernel like our default ones and Intel third generation CPU or higher. AMD users or older Intel users, or the Liquorix kernel, might be able to use PHC instead.

I just followed the install directions here: https://github.com/tiziw/iuvolt Note that you need bc and msr-tools installed. I then tried the sample command with their offset values, and the temperature dropped on my processor, which is running flat out compiling Krita, from around 152 F to around 145 F.

Pros: drops system CPU temperatures and increases battery life on laptops. Also saves power overall on AC. Go Captain Planet!

Cons: none so far on my machine, may make systems crash on other machines with those particular values.

If I want to start it automatically at system boot without running systemd, should I put that command in /etc/profile after saving the config?

Edit: looks like /etc/rc.local file is the correct location. And it seems that after suspend or hibernation resume the system goes back to the standard voltages, so you will need to add it to one of the pm-utils scripts.

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Krissharm
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Re: Undervolted my Skylake CPU-so far, so good!

#2 Post by Krissharm » Sat May 26, 2018 6:22 pm

Stupid question...
This slows down the CPU too? The link didn't state that. But that is what I assume?

Thanks for sharing. I've nothing new enough to take advantage yet, but its worth knowing that such a choice exists.
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Stevo
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Re: Undervolted my Skylake CPU-so far, so good!

#3 Post by Stevo » Sat May 26, 2018 7:16 pm

No, it keeps running at the same speed, just with a lower temperature. In fact, overclockers use it to keep the machines cooler when running at higher than normal speeds.

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Krissharm
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Re: Undervolted my Skylake CPU-so far, so good!

#4 Post by Krissharm » Sun May 27, 2018 4:50 pm

Amazing topic - lost hours looking into this - thank you
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antiX-Dave
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Re: Undervolted my Skylake CPU-so far, so good!

#5 Post by antiX-Dave » Sun May 27, 2018 11:26 pm

Do you have a good link explaining this theory?
I am not quite understanding.... How can you consume less power, keep the unit cooler, and maintain the same speed using the same hardware?

I keep thinking that in order to produce the same speed / work from the cpu while dropping the voltage would require a higher amperage. However higher amperage would turn out more heat... yet the cpu does not burn out... so if voltage is lower and amperage is lower because there is less heat, then how is the amount of work that the cpu is doing remain the same ?

I never delved into cpu benchmarking but I would have to guess that the work a cpu can do would be based on multiple factors... so is another factor crashing when clock speed is remaining the same?

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Re: Undervolted my Skylake CPU-so far, so good!

#6 Post by Krissharm » Mon May 28, 2018 12:38 am

The best that I can tell so far...
All the CPU's are built within a certain tolerance, so if the voltage is too low it will freeze/crash, playing with reducing it, you can sometimes get away with a lower voltage because its actually enough.
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skidoo
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Re: Undervolted my Skylake CPU-so far, so good!

#7 Post by skidoo » Mon May 28, 2018 1:10 am

it's a real thing (a win-win). Plenty of ongoing discussion about such things at overclockers.net
The notion of "silicon lottery" is well-established, documented, and the "spec'ced" voltage for a given CPU represents the midpoint of a mfg-tested range. Yeah, work per unit energy, looks good on paper but doesn't play out that way in practice. I don't know what you would consider to be a "definitive" reference, here's a couple links:

Should You Undervolt Your CPU? https://www.youtube.com/watch?v=AxaIZgzTbMA
https://en.wikipedia.org/wiki/Dynamic_voltage_scaling

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