Re: [Xen-devel] Estimating CPU utilization of DomU

[Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>]

Hi Guarav

  You should test by xentop, instead of libvirt.
Also you should write which kernel you are using.

Thanks
Atsushi SAKAI


Gaurav Dhiman <dimanuec@xxxxxxxxx> wrote:

> Hi All,
> 
> I am trying to implement a small script to estimate the CPU
> utilization of my DomU's from Domain-0 using libvirt APIs. I am using
> the virDomainInfo structure for that:
> 
> struct virDomainInfo{
> unsigned char state   : the running state, one of virDomainState
> unsigned long maxMem  : the maximum memory in KBytes allowed
> unsigned long memory  : the memory in KBytes used by the domain
> unsigned short        nrVirtCpu       : the number of virtual CPUs for the 
> domain
> unsigned long long    cpuTime : the CPU time used in nanoseconds
> }
> 
> So basically I query this structure for my DomU's every 'n' seconds,
> and get the CPU utilization by taking the difference of cpuTime (in
> seconds) and diving it by 'n'. To verify my estimates, I am running
> sar inside my DomU's (I do 100-%idle to estimate CPU util). It works
> perfectly for CPU intensive DomU's, but I observe some discrepancies
> for I/O intensive DomU's. My scripts shows higher CPU utilization than
> the sar output. Sometimes the difference is close to 10-15%. I am not
> sure what is the reason for this? Is there some time which the DomU
> VCPUs spend running, which sar cannot see? Or does the libvirt API add
> up the time spent by domain-0 for work done on behalf of DomU to its
> structure?
> 
> Any insights here would be really helpful!
> 
> Thanks,
> -Gaurav
> 
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