After reboot a lot of processes ran in the isolated cpus

doraemon

3/9/24, 1:03 PM

This question is migrated from stackoverflow since it was marked as off-topic there

I am running ubuntu 22.04 with kernel vmlinuz-5.19.0-35-generic. I isolated a few cpus by editing /etc/default/grub and did a sudo update-grub

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash isolcpus=4-7"

However, after I rebooted the system, I saw a lot of processes already running on one of the isolated CPUs, including some dockerd and systemd processes.

(I have rebooted for several times and observe the same)

I also checked /proc/cmdlin and dmesg. It does show that isolcpus is in the command line.

Is there a bug?

PS:

I also found some one saying similar, but don't know whether they are related.
There is a page on how to isolate cpus. when discussing the approach using isolcpus, it still asks to use cset to ping the docker and kubepods to the unshielded cpus. Does this mean that docker will generally not respect the isolcpus settings?

271

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kernel

cpu

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Ubuntu

gene-weber

5/9/24, 9:19 PM

Isolcpus did not work as I was expecting. I found an answer here. The two key points from that thread are:

It appears that presently, isolcpus= only affects user space threads, and hence, kernel threads will show up on the isolated CPU's.

In summary, Ubuntu isn't ignoring the option, it's working as intended. Whether it's working as desired is a different query.

+ 4

doraemon

5/10/24, 12:04 AM

For me, not only the kworkers, but the user apps are running in the isolated CPUS. If the user session leader is running there, all the children will be started over there and have no chance to be rescheduled to other threads.

Taylor R

5/11/24, 6:19 AM

This does not really answer the question. If you have a different question, you can ask it by clicking [Ask Question](https://askubuntu.com/questions/ask). To get notified when this question gets new answers, you can [follow this question](https://meta.stackexchange.com/q/345661). Once you have enough [reputation](https://askubuntu.com/help/whats-reputation), you can also [add a bounty](https://askubuntu.com/help/privileges/set-bounties) to draw more attention to this question. - [From Review](/review/late-answers/1297258)

gene-weber

5/11/24, 10:48 AM

@TaylorR You are correct. I intended it as more of a comment, but I didn't see a comment link when I wrote it. I edited it to try and make it as much of an answer as I can.

gene-weber

5/11/24, 10:51 AM

@doraemon I've given up on using isolcpus to try and keep one CPU clear for my real time process. I'm looking into cset now and can let you know how that works out.

Elon Musk

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EN: After reboot a lot of processes ran in the isolated cpus

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