high CPU usage for guest VM seen on Fedora host

asked 2017-03-30 11:20:51 -0500

iamauser gravatar image

I have a Fedora-23 (updated to kernel-4.8) as a VM host server. It is running a CentOS-7 and a few other custom distros as VMs.

The CentOS-7 guest VM is assigned 2 CPUs. During iperf3 tests on the CentOS-7 VM, for a high network throughput ( > 400 Mbps ), the CPU usage for the qemu pid shoots to 200% on the host. In the meantime, the guest VM, CPU usage < 10%. I use top -p <guest-vm-pid> to monitor the CPU usage on the host. I am using virtio for the guest network drivers.

There seems to be a strong correlation between the CPU usage seen on the host and the throughput.

Any suggestion or help regarding these questions would be appreciated.

Why is the discrepancy between the CPU usage seen on the guest and on the host ?

Why CPU usage seen on the host for the guest VM is so high when receiving high throughput ?

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