[fedora-virt] Virtualization: qemu-kvm: Excessive CPU usage on host

[Justin M. Forbes]

On Tue, Dec 15, 2009 at 04:37:32PM +0100, Dario Lesca wrote:
> Hello to everyone, on my laptop with F12x86_64 I have 'yum -y install 
> virtualization', then I installed a virtual machine F12x86_64 
> (without X, it's a server) for testing.
> 
> Unfortunately, when the guest machine is on and idle (does 
> anything) the host machine always has the cpu committed by the 15/25% 
> qemu-kvm. 
> 
> >  PID USER  PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> > 3584 qemu  20   0  764m 179m 3116 S 19.3  5.9  10:06.45 qemu-kvm
> 
> Also, after a bit of time (more than an hour) and the guest machine is
> unused, the process ksmd use excessive CPU (about 30%): another process 
> that slowed down with no apparent reason host (my laptop): 
> 
> >   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> >    32 root      25   5     0    0    0 R 30.1  0.0  39:00.62 ksmd
> >  3584 qemu      20   0  764m 523m 3116 S 15.9 17.3  31:59.25 qemu-kvm
> 
> All these things with VMware-server did not happen.
> 
> Is this normal? 
KSM has a penalty in that it requires CPU cycles to scan for usable pages.
This should be mitigated by the ksm service turning the scanner off when it
is not needed.
Do you have any more information on the hardware profile? Is there a smolt
profile for this system?

> It's possible do something to improve the situation? 
Is the ksmtuned service running?  If not, please turn it on.  Optionally
you can also turn off ksm and ksmtuned.


Thanks,
Justin