Re: about CPU QoS in KVM

[Paolo Bonzini <pbonzini@redhat.com>]

Adding Rik.

Paolo

On 20/04/2017 15:32, Gonglei (Arei) wrote:
> Hi all,
> 
> Currently, KVM do the CPU resource reservation by the cgroup mechanism
> which can't do entire accurate separation because the capacity of the Linux
> scheduler. Take the public cloud as an example, some customers rent one vm
> with 8 CPUs paid by enough money, they want to get enough response
> speed on CPU scheduling. So we (the cloud platform providers ) reserve 1GHz
> CPU resources by cgroup for those VM's vcpu/pcpu. 
> 
> But the actual effects can't meet those requirements because the cgroup is
> limiting share usage of other processes in order to attach the reservation proportion,
> but the scheduler can't assure that. This mechanism is different with Xen,
> We can directly change the CPU weight on Xen hypervisor so that we can
> get entire accurate control on CPU resources based on accurate capacity (upper limit),
> share (weight) and reservation.
> 
> So my question is do we have a good method to do CPU reservation in KVM?
> 
> Thanks,
> -Gonglei
> 
>