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I'm trying to measure the effects of cpu overcommitting on a KVM setup (both host and guest). I can detect performance is degraded when the number of vCPUs is increased but ideally I want to look at some more objective metric (like CPU Ready in esxtop). Is there an equivalent to esxtop for KVM that provides a similar metric.

Bhargav Rao
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pldimitrov
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1 Answers1

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There is a fundamental difference between how you monitor VMs in KVM and how you monitor them with ESXi.

Since a lot of people run KVM in Linux, I'm going to assume your underlying OS is a Linux based one.

How to get CPU Ready like functionality with KVM?

  1. With htop enable additional metrics and watch the gu section. This tells you how much CPU usage a guest is using.
  2. Use virt-top which tells you overall CPU usage (among other things) of a guest.

The oversubscription principles that apply to ESXi also apply to KVM. Although KVM does not use CPU bonding (by default) like ESXi does, you still do not want to go more than 1:5 ratio pCPU to vCPU ratio in KVM. Of course, this depends on how much you're utilizing the CPUs. You also do not want to give more CPU cores than necessary either. Start with 1 core and move up.