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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