Compute Challenge: Underclock* Your CPU

[plumpan]

* Underclock = use a less aggressive power mode

Ok hear me out

I imagine quite a few people here have newer AMD CPUs, Zen 2 and newer. For you all, I have a challenge: "Underclock" your CPU for a week.

How? Well don't actually underclock it because that's now how CPUs work nowadays. Change your OS's power settings. To avoid going into all of the details, I'd suggest just setting "Power Save" in your power mode settings. If you're on Linux, the incantation you want is "amd_pstate", and you have the same power option names as in Windows now: Performance, Balanced, and Power Save ("powersave"). Regardless of your OS, you'll probably end up with the same clock speed under load regardless of how many cores are active, a fair bit lower than even your all core speed would be normally. And the CPU will run much, much cooler.

You could mess around with eco mode settings in the bios but that's a big fuss, power profiles should get you most of the way there. Obviously if you've done manual overclocking, those probably won't work. I think these should still also work as expected even if you have PBO enabled.

This may also be possible on newer Intel CPUs but I'm not familiar with their clock scaling behavior at all and I'm not sure if they ever moved to something more dynamic than the old PL buckets.

The goal? Just to see how much you notice the difference, and if you think the difference matters. Do everything you normally would, see if running the CPU slower actually matters. I'd actually suggest not running any benchmarks other than some stress tests to see what your single/low/all core load clock speeds are before and after. After a week or so, you know exactly what it's like! Job done. You can also get some Bonus Points if you have a UPS or Kill-A-Watt to see what the change in power use is as well.

I've been on an older kernel on Linux and haven't had access to the newer p-state stuff, the OS options I have are "behave normally" or "lock all cores to 2.2GHz at all times". I can notice the difference at 2.2 but it's honestly not that bad, and the trade off is my CPU never gets hot enough to ramp the fans up. I run it like that more often than not now, only turning it off when I need to run a big video encode. I'm curious what it does with a newer kernel or if it just behaves the same on account of being an older Zen 2 CPU.

[dogbold_system]

linux nerd here.
amd_pstate is a whole kernel module, and i'm not quite sure how to get it to do what you're saying i can do with it. what are you talking about with it being an "incantation?"

[plumpan]

linux nerd here.
amd_pstate is a whole kernel module, and i'm not quite sure how to get it to do what you're saying i can do with it. what are you talking about with it being an "incantation?"

In reference to "Take this incantation to the homepage" from GCCX translations; "look up this phrase to understand what you need to do".

It means you want to look up how it works because exactly how you interact with it will change depending on your distro. And if you're on an older kernel you may be using a completely different driver to control such things that behaves entirely differently, like me.

Some distros/DEs have it entirely integrated into the UI so you can control it in quick settings (KDE and Gnome), some you might have to use something like power-profiles-daemon, some you may be manually echoing settings to the driver. Too many variables to try and cover in a quick post.

[a_random_fox]

Ok, sounds interesting. My own computer, which runs a Linux distro called Tuxedo OS, has a pretty good tool for that actually. Didn't use the default low power profile because the fan profiles that come with it are not that good (has a tendency to often switch between low and high fan speed), but the custom one wasn't that hard to make and it actually let me exactly specify the maximum amount of watts it is allowed to use. Results are to be seen, it currently is drawing about 7W as seen in the screenshot, but it already did that before selecting the profile as there wasn't much going on. The temperature being high is more due to the ambient temperature also being high than the CPU producing much heat.

I'd expect that most of the time i won't notice it as the CPU wouldn't need more power than the limits anyway, with the exceptions being games. Even with those, there are probably many that would still be fine, like older/retro games or visual novels.

[bunnyconda]

I do this with my GPU.

Recent-ish NVidia cards (not experienced with AMD but I assume it's not too different there) leave a lot of overhead for undervolting and through tweaking while running benchmarks I was able to cut some 35% (70W) off the max power draw with only 5% (if even that) performance loss, helps a ton with managing heat; on the more extreme end, I also made a script that locks the GPU's clock speeds to their lowest possible speed, and it's surprisingly easy to forget that it's enabled depending on what I'm doing.

[plumpan]

Ok, sounds interesting. My own computer, which runs a Linux distro called Tuxedo OS, has a pretty good tool for that actually. Didn't use the default low power profile because the fan profiles that come with it are not that good (has a tendency to often switch between low and high fan speed), but the custom one wasn't that hard to make and it actually let me exactly specify the maximum amount of watts it is allowed to use.

This is interesting. Whenever I can pick up a replacement NVMe for my laptop I'll throw Tuxedo on it and see what those options look like on the backend.

I do this with my GPU.

I've thought about stuff like this but my GPU is low enough power to begin with that I'm not as worried about it (100w or so) and I find just turning on vsync or otherwise frame capping games tends to whack the power consumption down immensely. This was actually very useful advice to a friend whose UPS was shutting down whenever they started up a game!

[a_random_fox]

Ok, sounds interesting. My own computer, which runs a Linux distro called Tuxedo OS, has a pretty good tool for that actually. Didn't use the default low power profile because the fan profiles that come with it are not that good (has a tendency to often switch between low and high fan speed), but the custom one wasn't that hard to make and it actually let me exactly specify the maximum amount of watts it is allowed to use.

This is interesting. Whenever I can pick up a replacement NVMe for my laptop I'll throw Tuxedo on it and see what those options look like on the backend.

Here is the source code on the developers website: https://github.com/tuxedocomputers/tuxe ... rol-center