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Hi Eoghan,

Thanks for your reply. As we can see from the document:
-------------------------------------------------------------------------

Three type of meters are defined in ceilometer:

Type 	Definition
Cumulative 	Increasing over time (instance hours)
Gauge 	Discrete items (floating IPs, image uploads) and fluctuating 
values (disk I/O)
Delta 	Changing over time (bandwidth)

----------------------------------------------------------------------------------------

Cumulative type is apparent, while even with descriptions gauge and 
delta type confuse me.
Could you explain them through examples or by sharing an use case?


Thanks

-----------------------
Yawei Wu
Dalian Hi-Think Computer Technology,Corp.


>
> Hi Yawei Wu,
>
> The root of the confusion is the fact the cpu meter is reporting
> the cumlative cpu_time stat from libvirt. This libvirt counter is
> reset when the associated qemu process is restarted (an artifact
> of how cpuacct works).
>
> So when you stop/start or suspend/resume, a fresh qemu process
> is sparked up, then the cumulative time is reset.
>
> Thanks for bringing this up, as it has implications as to how
> we meter CPU time and utilization[1].
>
> We may need to start metering the delta between CPU times on
> subsequent polling cycles, instead of using a cumulative meter
> (dealing with the edge case where the instance has been restarted
> within a polling period).
>
> Cheers,
> Eoghan
>
> [1] https://review.openstack.org/14921
>
>
>> I am still testing ceilometer now. I am confused about the meter
>> volume
>> in the mongodb. Let's talk about cpu usage.
>>
>> After I create and boot a vm named vm_1, meter data record about cpu
>> usage will be inserted into db in cycle(default 10 minutes). For
>> example,the 'counter_volume' of the first record is '52060000000',and
>> the second one is '123890000000'.
>>
>> 1) '123890000000' nanoseconds means '123.89' seconds or two
>> minutes,it
>> seem like to be 1238.9 seconds actually, is there something wrong ?
>>
>> 2) If I never reboot or suspend vm_1, will the 'counter_volume' of
>> cpu
>> usage record increase all the time ? Just like '8 minutes' -> '18
>> minutes' -> '28 minutes' ?
>>
>> 3) If I reboot or suspend vm_1, I find that the 'counter_volume' of
>> cpu
>> usage record will count from zero. Just like '8 minutes' -> '18
>> minutes'
>> -> '28 minutes' [-> '0 minutes'] ->'5 minutes' -> '15 minutes'. Does
>> it
>> mean that 'counter_volume' just represents how long has vm_1 been
>> booted
>> up ?
>>
>> 4) This one is about Web API. I find that "GET
>> /v1/resources/(resource)/meters/(meter)/volume/sum" just return the
>> sum
>> value of all the cpu 'counter_volume', like '8 minutes' + '18
>> minutes'.
>> Is it reduplicate ?
>>
>> 5) If I want to know how long has vm_1's cpu been used yesterday, how
>> can I do ?
>>
>> It seems like that I have too many questions..
>>
>> Thank you very much !
>>
>>
>> -----------------------
>> Yawei Wu
>> Dalian Hi-Think Computer Technology,Corp.
>>
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