linux-kernel - Re: about CPU QoS in KVM

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Date:   Tue, 25 Apr 2017 11:13:03 +0100
From:   Juri Lelli <juri.lelli@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     KVM list <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        cgroups@...r.kernel.org, Gonglei <arei.gonglei@...wei.com>,
        "Jason Wang (jasowang@...hat.com)" <jasowang@...hat.com>,
        "Huangweidong (C)" <weidong.huang@...wei.com>,
        linqiangmin@...wei.com, Rik van Riel <riel@...hat.com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        carlo.vitucci@...csson.com
Subject: Re: about CPU QoS in KVM

Hi,

just noticed this and thought I might just jump in. :)

On 20/04/17 16:00, Paolo Bonzini wrote:
> 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

Not entirely sure what your particular requirements are Gonglei, but you
might be interested to know that there has been research work [1,2,3,
just to name a few] that used a mainline real-time scheduling policy
(SCHED_DEADLINE) to provide Qos support to virtual machines (KVM).

I won't enter in too much detail, but the basic idea is to use
reservation based scheduling mechanisms to enforce temporal isolation and
guaranteed CPU bandwidth to VM's vcpu(s).

I'm Cc-ing Tommaso, Luca and Carlo, whom can provide more information as
needed.

Best,

- Juri

[1] - http://retis.sssup.it/~nino/publication/rtlws14sdnnfs.pdf
[2] - http://retis.sssup.it/~tommaso/publications/VHPC-2010.pdf
[3] - http://retis.sssup.it/~tommaso/publications/RTSOAA-2009-RTV.pdf

Skimming through Tommaso and Luca publications might be interesting as
well. I'm pretty sure I missed the most importants papers. :)
http://retis.sssup.it/~tommaso/eng/publications.html
https://scholar.google.co.uk/citations?user=C3a6glEAAAAJ&hl=en