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

[Gui Jianfeng]

On 2011-9-2 9:58, Zhi Yong Wu wrote:
> On Fri, Sep 02, 2011 at 09:16:59AM +0800, Gui Jianfeng wrote:
>> Message-ID: <4E602E8B.6010900 at cn.fujitsu.com>
>> 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>
>> References: <20110901050531.GB17963 at f15.cn.ibm.com>
>> <20110901081149.GB14245 at stefanha-thinkpad.localdomain>
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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.

Ahh, I misunderstand you before. I thought you mentioned the blkio cgroup throttling
interfaces. 
Ok, I think QEmu I/O throttling has similar semantic with blkio cgroup. So extending
blkiotune command is preferred, IMHO.

Thanks,
Gui

> 
> 
> Regards,
> 
> Zhi Yong Wu
> 
>>
>> Thanks,
>> Gui
>>
>>>
>>> Stefan
>>>
>>>
>>
>>
>>
> 
>