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

[Osier Yang <jyang@redhat.com>]

于 2011年09月01日 11:55, Zhi Yong Wu 写道:
> On Wed, Aug 31, 2011 at 08:18:19AM +0100, Stefan Hajnoczi wrote:
>> Subject: Re: The design choice for how to enable block I/O throttling
>> function in libvirt
>> From: Stefan Hajnoczi<stefanha@gmail.com>
>> To: Adam Litke<agl@us.ibm.com>
>> Cc: libvir-list@redhat.com, "Daniel P. Berrange"<berrange@redhat.com>, Zhi
>> Yong Wu<wuzhy@linux.vnet.ibm.com>, Zhi Yong Wu<zwu.kernel@gmail.com>
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>> On Tue, Aug 30, 2011 at 2:46 PM, Adam Litke<agl@us.ibm.com>  wrote:
>>> On Tue, Aug 30, 2011 at 09:53:33AM +0100, Stefan Hajnoczi wrote:
>>>> On Tue, Aug 30, 2011 at 3:55 AM, Zhi Yong Wu<zwu.kernel@gmail.com>  wrote:
>>>>> I am trying to enable block I/O throttling function in libvirt. But
>>>>> currently i met some design questions, and don't make sure if we
>>>>> should extend blkiotune to support block I/O throttling or introduce
>>>>> one new libvirt command "blkiothrottle" to cover it or not. If you
>>>>> have some better idea, pls don't hesitate to drop your comments.
>>>> A little bit of context: this discussion is about adding libvirt
>>>> support for QEMU disk I/O throttling.
>>> Thanks for the additional context Stefan.
>>>
>>>> Today libvirt supports the cgroups blkio-controller, which handles
>>>> proportional shares and throughput/iops limits on host block devices.
>>>> blkio-controller does not support network file systems (NFS) or other
>>>> QEMU remote block drivers (curl, Ceph/rbd, sheepdog) since they are
>>>> not host block devices.  QEMU I/O throttling works with all types of
>>>> -drive and therefore complements blkio-controller.
>>> The first question that pops into my mind is: Should a user need to understand
>>> when to use the cgroups blkio-controller vs. the QEMU I/O throttling method?  In
>>> my opinion, it would be nice if libvirt had a single interface for block I/O
>>> throttling and libvirt would decide which mechanism to use based on the type of
>>> device and the specific limits that need to be set.
>> Yes, I agree it would be simplest to pick the right mechanism,
>> depending on the type of throttling the user wants.  More below.
>>
>>>> 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.
>
> Danial and other maintainers,
>
> If you are available, can you make some comments for us?:)

Seems you posted to wrong list? This should be discussed in libvir-list
instead.

And if you meant to post to libvir-list, then s/Danial/Daniel/  :-)

>
> Regards,
>
> Zhi Yong Wu
>> Stefan