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I'm tracking CPU usage on a VM on a lightly-loaded host. Everything appears to be functioning normally on all the VMs, but collectd is reporting a gradually increasing 'steal' time:

enter image description here

The actual steal time reported is always either 100% or 0%, but as time passes, the 100% spikes get closer and closer together.

Both VM and host are running vanilla Debian 8. We didn't notice the same effect when both were running Debian 7 on a different physical host.

Is this a quirk of collectd or is KVM really slowly taking CPU resources away from the VM?

  • I remember we have a in-house software that didn't free memory... Then we forced to use valgrind profiler. Do you have any in-house program? – PersianGulf Jun 20 '15 at 18:49
  • However if you don't have any in-house program , You can try-testing via some memory analyzer. – PersianGulf Jun 20 '15 at 18:50
  • Memory usage is roughly constant at about 170Mb/512Mb the whole time. – Jack Douglas Jun 20 '15 at 19:55
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CPU steal time is (according to man proc):

Stolen time, which is the time spent in other operating systems when running in a virtualized environment.

If you have more than one VM on that host; or if you keep adding VM's on that host; or if you're overcommitting resources (especially CPU) you can run into this issue. I made a post about how overcommitting resources is bad in a virtual environment that may also be of help.

  • "If you have more than one VM on that host; or if you keep adding VM's on that host; or if you're overcommitting resources (especially CPU) you can run into this issue." — which if these will cause a linearly increasing 'steal' time lik in the graph? – Jack Douglas Nov 9 '15 at 17:44
  • Memory use is constant and CPU is fairly low the whole time (except for the 'steal' time which is obviously an artifact). – Jack Douglas Nov 10 '15 at 18:42
  • It's a KVM host running vanilla Debian 8 (as mentioned in the question). At the time there were no other VMs running and it made no difference as other guests were added, the steal time behaved exactly the same. – Jack Douglas Nov 11 '15 at 7:26

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