Subject: Re: about CPU QoS in KVM
To: KVM list <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        cgroups@vger.kernel.org
References: <33183CC9F5247A488A2544077AF19020DA237684@DGGEMA505-MBS.china.huawei.com>
Cc: Gonglei <arei.gonglei@huawei.com>,
        "Jason Wang (jasowang@redhat.com)" <jasowang@redhat.com>,
        "Huangweidong (C)" <weidong.huang@huawei.com>, linqiangmin@huawei.com,
        Rik van Riel <riel@redhat.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <8a5470cd-0cb2-5019-c7d3-7c407e6a6005@redhat.com>
Date: Thu, 20 Apr 2017 16:00:50 +0200
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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
> 
>