Coding

Ryzen Ubuntu Server: Throttle CPU Frequency for power saving

This is a super quick one, I have a Ryzen server running a bunch of VMs. I noticed it’s running quite hot and pulling a fair bit of power.

As none of the VMs running are particularly performance sensitive I wanted to force the CPU to use a more conservative power setting.

First up, how do I see what frequencies the CPU is currently running at? For that we’ll use cpufreq-info, this will tell us what frequency each core is at:

cpufreq-info | grep current
  current policy: frequency should be within 2.20 GHz and 3.60 GHz.
  current CPU frequency is 4.23 GHz.
  current policy: frequency should be within 2.20 GHz and 3.60 GHz.
  current CPU frequency is 2.70 GHz.
.... more

Now how do I see what power draw this is causing, well that’s more complicated. In my case I have an APC UPS connected to the system to keep it up during power outages. This has a tool called apcaccess which gives me information about the UPS’s load. Knowing the size of the UPS you can back track from the load % to a rough watt’s usage.

In our case what I want to do though is use this to prove that changing the CPU has worked. Before making any changes it outputs 19% load.

apcaccess | grep LOADLOADPCT  : 19.0 Percent

To throttle the CPU we can use a govenor lets see what governors we have available

cpufreq-info | grep governors
  available cpufreq governors: conservative, ondemand, userspace, powersave, performance, schedutil
  available cpufreq governors: conservative, ondemand, userspace, powersave, performance, schedutil
  available cpufreq governors: conservative, ondemand, userspace, powersave, performance, schedutil
  available cpufreq governors: conservative, ondemand, userspace, powersave, performance, schedutil

Cool, well powersave looks like a good one to try out, lets give that a go by running sudo cpupower frequency-set --governor powersave and then looking at the load and frequencies again.

lawrencegripper@libvirt:~$ sudo cpupower frequency-set --governor powersave
Setting cpu: 0
Setting cpu: 1
Setting cpu: 2
....
Setting cpu: 15
lawrencegripper@libvirt:~$ cpufreq-info | grep current
  current policy: frequency should be within 2.20 GHz and 2.20 GHz.
  current CPU frequency is 2.20 GHz.
  current policy: frequency should be within 2.20 GHz and 3.60 GHz.
  current CPU frequency is 2.20 GHz.
  current policy: frequency should be within 2.20 GHz and 3.60 GHz.
  current CPU frequency is 2.20 GHz.
....
lawrencegripper@libvirt:~$ apcaccess | grep LOAD
LOADPCT  : 15.0 Percent

That did the trick, apcaccess is reporting a drop to 15% load and CPU frequency is down to 2.2GHz.

I’ve got a smart meter for my home and can also see the drop in usage roughly reflected there too.

Done. Server is now being more eco-friendly.

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