Currently the cat /proc/pid/stat where pid is the pid of the VM Qemu
process gives the utime + stime of the VM according to libvirt.
Unfortunately I notice that this is actually the elapsed time of the host
. I find this by using libvirt , sampling the cputime of each VM
process and compare it to the total elapsed time (of the Host Linux
machine) . Roughly assuming full VM vcpu utlization, the cpu utilization
of every VM is actually : ( # of VM vcpus / total # of Host cpus) .This
implies that there is no idle time per VM (while actually there is) . We
only know the idle time of the Host via the top command at the Host .
Is the cputime of a VM (from cat /proc/pid/stat of the Qemu process as
used by libvirt) realy the cputime of the VM ?
I tested with a host having 2 sockets X 4cpus =8 totally and assigned
4 cpus to VM1 and VM2 . libvirt gave equal cputime for each VM which is
equal to the total machine elapsed time. But even if VM1 has 4 vcpus and
VM2 have 8 vcpus the cputime of each VM
(from cat /proc/pid/stat) is the elapsed time.
The truth is that I am running the libvirt application on the host machine
and do the application wait there . Should that matter much?
Each guest idle time is needed from the KVM for real cpu utilization
calc to be independent from the guest OS .
At least for Linux we can manually run 'top' at each guest terminal
window , but I do not know if it will show the real idle time or the total
machine (host) idle time .At least linux has no idle process . Besides
this is not a good programmatic way to get the VM idle time.
Is there a cure or I am missing something ?
thanks
Zvi Dubitzky
Virtualization and System Architecture Email:dubi@il.ibm.com
IBM Haifa Research Laboratory Phone: +972-4-8296182
Haifa, 31905, ISRAEL