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Re: [libvirt] [RFC][PATCHv1 2/5] libvirt - new API for getting percpu statistics of VM



2011/4/20 KAMEZAWA Hiroyuki <kamezawa hiroyu jp fujitsu com>:
> On Tue, 19 Apr 2011 12:29:05 +0100
> "Daniel P. Berrange" <berrange redhat com> wrote:
>
>> On Fri, Apr 15, 2011 at 04:43:03PM +0900, KAMEZAWA Hiroyuki wrote:
>> > On Fri, 15 Apr 2011 09:43:15 +0200
>> > Matthias Bolte <matthias bolte googlemail com> wrote:
>> >
>> > > 2011/4/15 KAMEZAWA Hiroyuki <kamezawa hiroyu jp fujitsu com>:
>> > > Also do you really need the absolute CPU time?
>> > yes, for virt-top -1.
>>
>> I don't think that is correct. What virt-top ultimately displays
>> to the end user is a % utilization. So it would be happy to get
>> data in either % util & display that directly, or get absolute
>> CPU time and calculate deltas to display % util.
>>
>
> virt-top calculate delta by itself.
>
>
>> I wonder if we could provide an API that could be used to provide
>> either per-VCPU or per-PCPU  statistics in one go, so that we
>> can finally have an API for cpu time that works well for VMWare.
>>
>
> VMWare ?
>

VMware can provide various statistics about a virtual machine, but
most (actually all, I think) are not provided as absolute values but
in 20 sec slots with 1h of history (a vCenter can store longer
history). Therefore, it's nearly impossible to get the absolute CPU
time of a virtual machine since bootup.

In most cases the enduser is not interested in the absolute CPU time
but in the current CPU utilization in percent. VMware already
calculates the utilization, but libvirt currently has not API to
expose that.

http://www.vmware.com/support/developer/vc-sdk/visdk41pubs/ApiReference/vim.PerformanceManager.html
http://www.vmware.com/support/developer/vc-sdk/visdk41pubs/ApiReference/cpu_counters.html

Matthias


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