I have a Debian machine with 4 CPU cores running Xen with two virtual machines, and I'm having trouble determining overall real CPU usage.

Each machine has two VCPUs assigned to it with no cap on CPU use:

Domain-0                             0    256    0
dom01                                1    256    0
dom02                                4    256    0

While logged into each of those machines, top shows 80-90% CPU usage on each CPU (I press '1' to show each core individually). xentop on dom0 agrees with this report.

However, top on dom0 shows all 4 CPU cores spending most of their time idle.

Does xen hide the CPU utilization of the virtual environments from dom0's top? If so, is there any way to display the real utilization of the CPU cores on the machine?

1 Answer 1


Correct, dom0 doesn't see domU CPU activity.

The answer is in your question: xentop on dom0 shows you the real utilization of the CPUs.

  • 1
    I don't see any way to view the utilization of individual CPU cores in xentop, only the total CPU % used by each virtual machine. Is there any way to get a per-core total? Nov 24, 2011 at 22:17
  • To get a per-core total of CPU usage hit V in xentop.
    – MikeyB
    Nov 24, 2011 at 22:22
  • That gives per-VCPU total seconds. But no CPU %, which is what I'm after. Nov 24, 2011 at 22:25
  • … yeah, you asked for a 'per-core total'.
    – MikeyB
    Nov 24, 2011 at 22:26
  • If it's important to you to see CPU%, you can try adding that functionality to xentop :) Or source dive to figure out where it's getting the information from.
    – MikeyB
    Nov 24, 2011 at 22:27

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