Re: [libvirt-users] cpuTimes and qemu-kvm on F13
On Fri, Aug 13, 2010 at 08:42:21PM -0400, Matthew Farrellee wrote:
http://libvirt.org/html/libvirt-libvirt.html#virDomainInfo
http://libvirt.org/html/libvirt-libvirt.html#virVcpuInfo
Both virDomainInfo and virVcpuInfo have a nanosecond cpuTime field. How
do the two related to one another?
With some experiementing, it appears the virDomainInfo::cpuTime is equal
to the host CPU time used by the qemu-kvm process for the domain. It
also appears that the sum(virVcpuInfo::cpuTime) for a domain is not
equal to the virDomainInfo::cpuTime. Is the virVcpuInfo::cpuTime how
much host CPU time was spent simulating the vCPU? Making the difference
between the sum and the virDomainInfo::cpuTime the overhead of qemu-kvm?
Yes, virVcpuInfo::cpuTime is the execution time for a single vCPU,
while virDomainInfo::cpuTime is execution time for the whole VM.
QEMU has other non-VCPU threads, eg I/O threads, which is where
the discrepancy you see comes in.
Does the relationship hold for other hypervisors?
Yes & no. The 'whole VM' execution time is somewhat hard to actually
define & report. eg QEMU with vhost enabled has a kernel thread
doing some work that we are unable to report/account under the
'whole VM' time. With Xen meanwhile the 'whole VM' time is only
really counting the time associated with the guest domain context,
not stuff running in Dom0 context on behalf of the VM - eg qemu-dm
time. IIUC, with stub domains that is resolved
Daniel
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