Re: Estimating CPU utilization of DomU

[Gaurav Dhiman <dimanuec@gmail.com>]

On Fri, Jul 16, 2010 at 1:19 AM, Atsushi SAKAI <sakaia@jp.fujitsu.com> wrote:
> Hi Guarav
>
>  You should test by xentop, instead of libvirt.
> Also you should write which kernel you are using.
>

Thanks for your reply. I will test with xentop as well. But what is
wrong with libvirt? Ultimately both of them use Xen APIs, right? I am
using Linux 2.6.30 pv_ops kernel as my Dom0, and Linux 2.6.18-xen
kernel (from the Xen website) as my DomU.

Thanks,
-Gaurav


> Gaurav Dhiman <dimanuec@gmail.com> 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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>
>
>