[libvirt] [RFC] block I/O throttling: how to enable in libvirt

[Zhi Yong Wu]

On Thu, Sep 01, 2011 at 09:49:34AM +0100, Daniel P. Berrange wrote:
>From: "Daniel P. Berrange" <berrange at redhat.com>
>To: Stefan Hajnoczi <stefanha at gmail.com>
>Cc: Zhi Yong Wu <wuzhy at linux.vnet.ibm.com>, libvir-list at redhat.com,
> agl at us.ibm.com, qemu-devel at nongnu.org, guijianfeng at cn.fujitsu.com,
> hutao at cn.fujitsu.com, zwu.kernel at gmail.com
>Subject: Re: [RFC] block I/O throttling: how to enable in libvirt
>Message-ID: <20110901084934.GA14462 at redhat.com>
>Reply-To: "Daniel P. Berrange" <berrange at redhat.com>
>References: <20110901050531.GB17963 at f15.cn.ibm.com>
> <20110901081149.GB14245 at stefanha-thinkpad.localdomain>
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>On Thu, Sep 01, 2011 at 09:11:49AM +0100, Stefan Hajnoczi wrote:
>> On Thu, Sep 01, 2011 at 01:05:31PM +0800, Zhi Yong Wu wrote:
>> > On Wed, Aug 31, 2011 at 08:18:19AM +0100, Stefan Hajnoczi wrote:
>> > >On Tue, Aug 30, 2011 at 2:46 PM, Adam Litke <agl at us.ibm.com> wrote:
>> > >> On Tue, Aug 30, 2011 at 09:53:33AM +0100, Stefan Hajnoczi wrote:
>> > >>> I/O throttling can be applied independently to each -drive attached to
>> > >>> a guest and supports throughput/iops limits.  For more information on
>> > >>> this QEMU feature and a comparison with blkio-controller, see Ryan
>> > >>> Harper's KVM Forum 2011 presentation:
>> > >>
>> > >>> http://www.linux-kvm.org/wiki/images/7/72/2011-forum-keep-a-limit-on-it-io-throttling-in-qemu.pdf
>> > >>
>> > >> From the presentation, it seems that both the cgroups method the the qemu method
>> > >> offer comparable control (assuming a block device) so it might possible to apply
>> > >> either method from the same API in a transparent manner.  Am I correct or are we
>> > >> suggesting that the Qemu throttling approach should always be used for Qemu
>> > >> domains?
>> > >
>> > >QEMU I/O throttling does not provide a proportional share mechanism.
>> > >So you cannot assign weights to VMs and let them receive a fraction of
>> > >the available disk time.  That is only supported by cgroups
>> > >blkio-controller because it requires a global view which QEMU does not
>> > >have.
>> > >
>> > >So I think the two are complementary:
>> > >
>> > >If proportional share should be used on a host block device, use
>> > >cgroups blkio-controller.
>> > >Otherwise use QEMU I/O throttling.
>> > Stefan,
>> > 
>> > Do you agree with introducing one new libvirt command blkiothrottle now?
>> > If so, i will work on the code draft to make it work.
>> 
>> No, I think that the blkiotune command should be extended to support
>> QEMU I/O throttling.  This is not new functionality, we already have
>> cgroups blkio-controller support today.  Therefore I think it makes
>> sense to keep a unified interface instead of adding a new command.
>
>Agreed, the virDomainGetBlkioParameters/virDomainSetBlkioParameters
>APIs, and blkio virsh command are intended to be a generic interface
>for setting any block related tuning parameters, regardless of what
>the underling implementation is. So any use of QEMU I/O throttling
>features should be added to those APIs/commands.
thanks for your suggestions.

Regards,

Zhi Yong Wu
>
>
>Daniel
>-- 
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