Ubuntu 20.04 disable cpu core?

Multi_ · May 2021

Hello guys,

I do have a vps with 3 cores which I am allowed to use 75% 24/7. So I thought disabling one of the 3 cores to max out 2 cores 24/7 would be my way to go.

I tried to disable one core by editing the /etc/default/grub and adding maxcpus=2 but after running update-grub and restarting the cpu2 is still online.

Is there anything differnt in newer ubuntu versions so this method does not work?

Thanks in advance.

ehab · May 2021

with your last setting , did you try to make a workload that uses all cpu and check from htop what is being used?

Multi_ · May 2021

@ehab said:
with your last setting , did you try to make a workload that uses all cpu and check from htop what is being used?

No, I just checked htop to see how many cpus are avaible and took a look at /sys/devices/system/cpu/cpu2/online if it's online. Did not think of it might show up but is not being used.

yoursunny · May 2021

@Multi_ said:
I do have a vps with 3 cores which I am allowed to use 75% 24/7. So I thought disabling one of the 3 cores to max out 2 cores 24/7 would be my way to go.

420 special, isn't it?
https://talk.lowendspirit.com/discussion/comment/62861/#Comment_62861

@Multi_ said:
took a look at /sys/devices/system/cpu/cpu2/online if it's online.

Do you know you can write to this file?
Write a 0 and the CPU is offline.

Bochi · May 2021

If it is a single process, that is producing the load you could use taskset to set its affinity.
Or create a cpu cgroup with some limits for a whole set of processes and its threads, maybe even in combination with a cpuset.

Multi_ · May 2021

@yoursunny said:

@Multi_ said:
I do have a vps with 3 cores which I am allowed to use 75% 24/7. So I thought disabling one of the 3 cores to max out 2 cores 24/7 would be my way to go.

420 special, isn't it?
https://talk.lowendspirit.com/discussion/comment/62861/#Comment_62861

Yes, exactly.

@Multi_ said:
took a look at /sys/devices/system/cpu/cpu2/online if it's online.

Do you know you can write to this file?
Write a 0 and the CPU is offline.

I can do that, but after a restart it's online again.

ehab · May 2021

@Multi_ said:
I can do that, but after a restart it's online again.

google sysctl.d

Multi_ · May 2021

@ehab said:

@Multi_ said:
I can do that, but after a restart it's online again.

google sysctl.d

Sorry for the late reply.

I am unable to set the amount of cpu cores with a sysctl config. According to this list the "maxcpus" parameter is a kernel parameter but I am unable to use that in a config.

I am really sorry but I am kinda new to the topic Kernels and their parameters. Until now it just worked for me ^^

teamacc · May 2021

Are you sure you're allowed to max 75% of all 3 cores? Linux tends to list cpu usage as percentage of a single core, ie maxing out 2 cores would result in 200% cpu usage.

Could be that your provider has (rightfully so in my opinion) put the limit below 1 core all the time, since it's a shared environment.

InceptionHosting · May 2021

@teamacc said:
Are you sure you're allowed to max 75% of all 3 cores? Linux tends to list cpu usage as percentage of a single core, ie maxing out 2 cores would result in 200% cpu usage.

Could be that your provider has (rightfully so in my opinion) put the limit below 1 core all the time, since it's a shared environment.

If I had €1 for every time I have had to explain that.... well I would not be a millionaire but it would be a good chunk of change..

People are so quick to look for loopholes to get dedicated resources on a shared resource environment.

If the host wanted to they will just kill your cpu weight in the back end anyway I guess

Maybe just ask your host to remove a core for you? If you are confident that is what you paid for it should not be a problem right?

yoursunny · May 2021

@Multi_ said:

@Multi_ said:
took a look at /sys/devices/system/cpu/cpu2/online if it's online.

@yoursunny said:
Do you know you can write to this file?
Write a 0 and the CPU is offline.

I can do that, but after a restart it's online again.

Create a custom systemd service to write the file upon start, and make that service auto start.

@teamacc said:
Are you sure you're allowed to max 75% of all 3 cores? Linux tends to list cpu usage as percentage of a single core, ie maxing out 2 cores would result in 200% cpu usage.

Terms of Service for 420 special: https://hosterlabs.net/tos/
Archive link: http://web.archive.org/web/20210420230451/https://hosterlabs.net/tos/

"CPU Abuse is defined as: You might not use more than 75% of a shared CPU resource for more than 72 hours in a given week or 6 straight hours."

This applies to every plan.
It's only reasonable to interpret as "75% of all cores", otherwise there would be no difference paying for 1 core or 6 cores.

Moreover, the provider themselves said "technically yes" when I asked: https://talk.lowendspirit.com/discussion/comment/62863/#Comment_62863

@InceptionHosting said:
People are so quick to look for loopholes to get dedicated resources on a shared resource environment.

If the host wanted to they will just kill your cpu weight in the back end anyway I guess

I know.
It's like docker run --cpus 0.02, and everything in the container slows to a crawl.
Oracle Cloud and EUserv are definitely doing that.
VirMach is probably doing that.

I have no problem with that, and I even prefer a permanent throttling of every resource.
I hate having to set CPU limits on every process myself, and still worry about a suspension hammer.

InceptionHosting · May 2021

I read “a shared cpu resource” as a (singular) thread or core.

I am not just saying that to take an opposing view, that is honestly how I understood it on initial reading so it needs some clarification IMO.

Ubuntu 20.04 disable cpu core?

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