On Sun, Mar 22, 2009 at 02:28:00PM +0200, Zvi Dubitzky wrote:
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 ?
I have a host machine with 8 cpus I run 2 guests, one with 4 vcpus, and one with 1 vcpu. Inside the first guest I run 4 copies of while /bin/true ; do /bin/true ; done This generates 100% cpu usage within the guest If I run 'virt-top' on the host machine, I see that guest reported as using 50% cpu. This is accurate because 4 cpus in guest, 100% utilized is 1/2 of the total resources available to the host which has 8 cpus. Similarly if i run that load generator on the 2nd guest, which only has 1 vcpu, then virt-top again correctly shows that guest as using 12.5% of total host CPU resources (100% / 8 == 12.5%) So AFAICT, everything is working exactly as designed. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|