In the simple script, one can change a normal kernel to a Realtime PREEMPT kernel in Debian 9 and CentOS7.

bash rt_conf.bash

I don't recommend this script, please contact relevant persons to ask the real time kernel support. Even so, one would like to try this script (It may switch the entire environment to the generic one, one can revert these changes manually. There is no support on them.), please run the script with an argument as follows:

bash rt_conf.bash clean

• postfix
• sendmail
• cups

• ethtool

Current CentOS repositories have the broken dependency issues. This approach is weird, but we need to move forward. Please use the generic CentOS 7.

Use the default Debian repository

• Use the CERN CentOS 7 rt repository [1]. Note that CentOS 7 should be generic one.
• Disable all repositories in order to keep the one RT kernel

$ yum repolist
$ yum-config-manager --disable \*
$ yum repolist
Loaded plugins: fastestmirror, versionlock
repolist: 0

• Set the default kernel to the RT kernel

$ grubby --set-default-kernel=/boot/vmlinuz-3.10.0-1062.9.1.rt56.1033.el7.x86_64

One can check the default one via

$ grubby --default-kernel

According to the Reference [2], we select the minimum boot parameters as follows:

• idle=pool (with the assumption that TSC is selected as the system clock source)
• intel_idle.max_cstate=0
• processor.max_cstate=1
• skew_tick=1

The tuned kernel boot parameters have the requirement of TSC clock. Please check it and select TSC if not.

• Check the current clock source

cat /sys/devices/system/clocksource/clocksource0/current_clocksource

• Check the available clock source

cat /sys/devices/system/clocksource/clocksource0/available_clocksource

• Select the tsc (Time Stamp Counter) [2] as the current clock

echo tsc > /sys/devices/system/clocksource/clocksource0/current_clocksource

$ systemctl get-default
graphical.target
$ systemctl set-default multi-user.target
$ reboot

Disable Power Saving and other features.

At the baseline of the configuration, we would like not to use the irqbalance with Linux PREEMPT RT kernel. Note that one should check its status via systemctl status irqbalance after rebooting with RT kernel. Or one can use rt_check.bash.

>>> System service : irqbalance
● irqbalance.service - irqbalance daemon
   Loaded: loaded (/usr/lib/systemd/system/irqbalance.service; disabled; vendor preset: enabled)
   Active: inactive (dead)

[1] http:https://linux.web.cern.ch/linux/centos7/
[2] https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux_for_real_time/7/
[3] https://en.wikipedia.org/wiki/Time_Stamp_Counter