While building a small Citrix NetScaler… ehm… ADC VPX (I really hate this name…) lab environment, I noticed that the fan of my Lenovo T480s was spinning up. I was wondering why, because the VPX VM was just running for a couple of minutes – without any load. But the task manager told me, that the VMware Workstation Process was consuming 25% (I have a Intel i5 Quad Core CPU) CPU. So VMware Workstation was just eating a whole CPU core without doing anything. I would not care, but the fan… And it reminded me, that I’ve seen an similar behaviour in various VPX deployments on VMWare ESXi.
A quick search lead me to this Citrix Support Knowledge Center article: High CPU Usage on NetScaler VPX Reported on VMware ESXi Version 6.0. That’s exactly what I’ve observed.
The solution is setting the parameter cpuyield to yes.
> set ns vpxparam -cpuyield YES
> show ns runningConfig | grep "cpuyield"
set ns vpxparam -cpuyield YES
The VPX does not need a reboot. Short after setting the parameter, the fan stopped spinning. Have I mentioned how I love silence on my desk? I’m pretty happy that my T480s is a really quiet laptop.
But what does this parameter is used for? In pretty simple words: To allocate CPU cycles, that are not used by other VMs. Until ADC VPX 11.1, the VPX was sharing CPU with other VMs. This changed with ADC VPX 12.0. Since this release, the VPX was like a child, that was playing with their favorite toy just to make sure, that no other child can play with it. Not very polite…
This is a quote from the Support Knowledge Center article:
Set ns vpxparam parameters:
-cpuyield: Release or do not release of allocated but unused CPU resources.
YES: Allow allocated but unused CPU resources to be used by another VM.
NO: Reserve all CPU resources for the VM to which they have been allocated. This option shows higher percentage in hypervisor for VPX CPU usage.
I don’t think that I would change this in production. But for lab environments, especially if you run this on VMware Workstation, I would set -cpuyield to yes .