[libvirt-users] [API reference] confused by CPU time term

[Eric Blake]

On 04/16/2012 04:02 AM, Zhihua Che wrote:
> I find that the cpu_time returned by virDomainGetCPUStats is always
> increasing despite it's restarted.

That is the time attributed to a single domain.  Are you saying that the
value doesn't restart at 0 every time you stop and then restart the
domain?  That would be a problem, because my understanding is that each
new qemu process should start over at 0, because we should be
(re-)creating a new cgroup subdirectory for each new qemu process.

> 
> Precisely, after calling virDomainGetCPUStats, it return a array of
> virTypedParameter, each element for each cpu.
> one example is
> {
>     .fiedl = "cpu_time",
>     .type = 4,
>     .value.ul = 7744142223
> }
> 
> I guess this value is cumulative running time of the domain since it's
> created? Is that right?

Yes, virDomainGetCPUStats is documented as returning the cumulative time
attributed to the running of this particular domain from the perspective
of the current host.  At present, migration or managedsave would reset
these counts to 0 (as migration starts a new qemu process); perhaps we
need to consider enhancing the domain XML associated with live domains
in order to transfer cumulative run-time across migration scenarios?

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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