Manually balance IRQs or use irqbalance?
A good discussion of when manual IRQ balancing is and is not appropriate came up on the page where we posted a tech brief on the subject:
https://access.redhat.com/knowledge/techbriefs/optimizing-red-hat-enterprise-linux-performance-tuning-irq-affinity
If you have had success manually pinning IRQ interrupts to specific processors (or tried it and decided you didn't get the performance improvements you had hoped), feel free to contribute your experiences here.
Responses
This document is an excellent write up.. but unfortunately is now a little dated (2+ years). Are there any newer resources from Red Hat on irqbalance particularly in regards to irqbalance on virtual guests?
Is irqbalance relevant on a virtual guest? do Red Hat have a recommendation?
I have seen mention of running irqbalance on the KVM/RHEV host which makes sense, but I have concerns about how effective it is when using it in the guest with virtual processors.
I found some additional discussion here:
https://access.redhat.com/solutions/41535
The KB response essentially says there are some workloads that may require it (in a few more words).
Terry's first post also provides some insight (point 2.)
Virtual Guests. It does not really make sense because unless you are pinning the guest to specific CPUs and IRQs and dedicated net/storage hardware, you will likely not see the benefits you would on bare metal. But your KVM/RHEV host SHOULD be using irqbalance and numad and tuned.
Then Terry's second response provides guidance to use the virtual-guest tuned profile (not sure if this has irqbalance or not)
Any additional thoughts / recommendations from any irqbalance gurus out there?
I guess the real question I am asking isn't the benefit that it provides, but what negative impact can I expect (if any) if it's running in a VM?.
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