IRQBALANCE_BANNED_CPUS setting

[t3kg33k]

Hello, all. I've already posted this on Red Hat's community forum but, so far, no one has been able to provide any assistance and I am on a time crunch to get the solution for work.
I'm hoping someone could help with the following articles:

2.4. Interrupt and Process Binding Red Hat Enterprise Linux for Real Time 7 | Red Hat Customer Portal

Access Red Hat’s knowledge, guidance, and support through your subscription.

access.redhat.com

https://access.redhat.com/solutions/3152271 # If you can't access this, I have also attached it.


First, the following setting is made in our environment that was set by the Admin before me in /etc/sysconfig/irqbalance:


IRQBALANCE_BANNED_CPUS=000fffff


This is supposed to be set for CPUs 0-19. I'm actually having a difficult time understanding if that hex setting is correct for CPUs 0-19 per the Admin's intention. I could not find anywhere in the articles (and in my Google'ing) on how to tell if that setting is actually working as intended. One thing I have found on the systems that have that setting is if I run 'ps -aeF' I still see what looks to be irqs' on CPUs 0-19. Based on my understanding from the articles, I would have assumed I would NOT see any irq assigned to any of the CPUs 0-19.
The other thing I am trying to do and I'm a little confused on how to set is to add CPU 27 to that setting.
If anyone can assist, I would greatly appreciate it. This is for RHEL/CentOS 7.9.
Thanks.

 

[t3kg33k]

So, after further research, I think I came to a solution. First of all, if my configurations are correct, my CPU27, in hex, should b 8000000. Also, I think I can see the results from irqbalance -d...I think. I'm still trying to grasp the output of that command.

 

[f33dm3bits]

I have never tried this but looking at one of the examples in the documentation link you shared I would think it would look something like this.

IRQBALANCE_BANNED_CPUS=00000001,0000ff00

Because below that it says.

The above mask excludes CPUs 8 to 15 as well as CPU 33 from IRQ balancing.

 

[t3kg33k]

By my calculations based on this formula from the KB:

$ echo "obase=16;ibase=2;00001000000011111111111111111111" | bc | tr '[:upper:]' '[:lower:]'

I think my setting is supposed to be this since I want to continue to ban 0-19 and add 27 to the setting (my systems have more than 32 CPUS):

IRQBALANCE_BANNED_CPUS=000fffff, 8000000

But, I could be wrong, because math.