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

[Zhi Yong Wu]

On Fri, Sep 02, 2011 at 09:16:59AM +0800, Gui Jianfeng wrote:
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>Date: Fri, 02 Sep 2011 09:16:59 +0800
>From: Gui Jianfeng <guijianfeng at cn.fujitsu.com>
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>To: Stefan Hajnoczi <stefanha at gmail.com>, Zhi Yong Wu
> <wuzhy at linux.vnet.ibm.com>
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>Subject: Re: [Qemu-devel] [RFC] block I/O throttling: how to enable in
>	libvirt
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>On 2011-9-1 16:11, 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.
>Proportional controlling interfaces and throttling interfaces are all
>the same cgroup subsystem. So Just extend blkiotune to add new options
>to support throttling tuning.
Hi, Gui,
QEMU block I/O throttling is not relative to cgroup subsystem, i think.
anyway, thanks for your sugguests.


Regards,

Zhi Yong Wu

>
>Thanks,
>Gui
>
>> 
>> Stefan
>> 
>> 
>
>
>