Re: Limit the CPU usage of KVM

[Dor Laor <dlaor@redhat.com>]

On 08/17/2009 08:09 AM, Yu Jiang (yujia) wrote:
> Hi KVM experts,
>
> Our user case needs to run KVM and application on host together. To
> reserve some CPU resource for application, we want to limit the CPU
> usage of KVM. Without KVM CPU usage limitation, the idle CPU of host OS
> becomes 0% in peak time.
>
> I have searched this topic on internet, but didn't find much comments.
>
> One possible solution could be managing KVM process as regular process
> on host OS, and use tool like http://cpulimit.sourceforge.net/ to limit
> maximum CPU usage of VM. Basically, the cpulimit tool use SIGSTP and
> SIGCONT signals to stop and resume the execution of KVM process. It
> works fine for us at moment. But, I feel there may be some risk to do
> this, because the signal will cause whole process of KVM paused(not only
> vcpu thread). Do you think it's safe to use cpulimit kinds of tool to
> SIGSTP/SIGCONT kvm?
>
> Another possible solution was:
> Enhance QEMU user space to monitor the CPU usage of itself, and use
> existing way(pause_all_vcpus?) to pause vcpu thread of KVM in case KVM
> reaches CPU usage limitation. Is this solution possible?

A mgmt daemon can control qemu using the monitor and stop/cont it on 
these cases.

The main problem with the two solutions above is that the guest clock 
might drift. Moreover, you increase the latency for the guest 
OS/applications.

You can use the 'nice' command to priorities the host applications.
For newer kernels you should use cgroups that solves this specific issue 
exactly.

>
> Any idea?
>
>
> Thanks,
> Yu
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html