From: "Daniel P. Berrange" <berrange@redhat.com> To: Stefan Hajnoczi <stefanha@gmail.com> Cc: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>, libvir-list@redhat.com, agl@us.ibm.com, qemu-devel@nongnu.org, guijianfeng@cn.fujitsu.com, hutao@cn.fujitsu.com, zwu.kernel@gmail.com Subject: Re: [RFC] block I/O throttling: how to enable in libvirt Message-ID: <20110901084934.GA14462@redhat.com> Reply-To: "Daniel P. Berrange" <berrange@redhat.com> References: <20110901050531.GB17963@f15.cn.ibm.com> <20110901081149.GB14245@stefanha-thinkpad.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20110901081149.GB14245@stefanha-thinkpad.localdomain> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.67 on 10.5.11.12 X-Brightmail-Tracker: AAAAAA== X-Xagent-From: berrange@redhat.com X-Xagent-To: wuzhy@linux.vnet.ibm.com X-Xagent-Gateway: emeavsc.vnet.ibm.com (XAGENTU at EMEAVSC)
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@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-t...
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.
On Thu, Sep 01, 2011 at 09:49:34AM +0100, Daniel P. Berrange wrote: thanks for your suggestions. Regards, Zhi Yong Wu
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