Tuned-admin profile realtime does not work for ubuntu 20.04

Wei Qiu

7/14/24, 6:37 AM

I would isolate cores using tuned realtime profile.

I have modfiled /etc/tuned/realtime-variables.conf

# Examples:

isolated_cores=0-7

#
#
# Uncomment the 'isolate_managed_irq=Y' bellow if you want to move kernel
# managed IRQs out of isolated cores. Note that this requires kernel
# support. Please only specify this parameter if you are sure that the
# kernel supports it.
#
isolate_managed_irq=Y

and then run tuned-admin profile realtime

however, tuned does not add isolcpus to boot command line.

After reboot, I can still see processes scheduled to core 0-7.

1 + 0

realtime

20.04

Score:1

Ubuntu

Andrew Lowther

7/25/24, 10:58 PM

The tuned software is written for RedHat and there are a number of bugs with the package ported for Ubuntu. This looks like another one, but there may be a work around.

I duplicated your attempt and looked in /var/log/tuned/tuned.log. I see the lines

2023-07-25 22:31:07,931 INFO     tuned.plugins.plugin_bootloader: installing additional boot command line parameters to grub2
2023-07-25 22:31:07,932 ERROR    tuned.plugins.plugin_bootloader: cannot find grub.cfg to patch, you need to regenerate it by hand by grub2-mkconfig

Looking at the tuned source code I believe tuned is looking for the file /etc/grub2.cfg.

If I symlink this file then the profile does apply.

ln -s /boot/grub/grub.cfg /etc/grub2.cfg
tuned-adm profile realtime

Now the isolcpus argument is in /boot/grub/grub.cfg. I think the only file directly modified by tuned is /etc/tuned/bootcmdline.

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