On Thu, Sep 01, 2011 at 01:05:31PM +0800, Zhi Yong Wu wrote:
----- Forwarded message from Zhi Yong Wu <wuzhy@linux.vnet.ibm.com> ----- Date: Thu, 1 Sep 2011 11:55:17 +0800 From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com> To: Stefan Hajnoczi <stefanha@gmail.com> Cc: "Daniel P. Berrange" <berrange@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, Adam Litke <agl@us.ibm.com>, Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>, QEMU Developers <qemu-devel@nongnu.org>, guijianfeng@cn.fujitsu.com, hutao@cn.fujitsu.com Subject: [RFC] block I/O throttling: how to enable in libvirt Message-ID: <20110901035517.GD16985@f15.cn.ibm.com> References: <CAEH94Li_C=BOe2gV8NyM48njYWMBAo9MTGc1eUOh-Y=cODs6VA@mail.gmail.com> <CAJSP0QW1CPCokX=F5z7y==vn1S4wH0VtOaQ7oj4kC7f7uQM4MQ@mail.gmail.com> <20110830134636.GB29130@aglitke.rchland.ibm.com> <CAJSP0QUHm=y8XJC_KXRg7ufFZt3K_XDDfQb--sxjC+c0GjO8qg@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <CAJSP0QUHm=y8XJC_KXRg7ufFZt3K_XDDfQb--sxjC+c0GjO8qg@mail.gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Xagent-From: wuzhy@linux.vnet.ibm.com X-Xagent-To: wuzhy@linux.vnet.ibm.com X-Xagent-Gateway: vmsdvma.vnet.ibm.com (XAGENTU7 at VMSDVMA)
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> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Brightmail-Tracker: AAAAAA== X-Xagent-From: stefanha@gmail.com X-Xagent-To: wuzhy@linux.vnet.ibm.com X-Xagent-Gateway: bldgate.vnet.ibm.com (XAGENTU7 at BLDGATE)
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-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.
Daniel and other maintainers,
If you are available, can you make some comments for us?:) HI, Adam, Now stefan, Daniel, and Gui all suggest extending blkiotune to keep libivrt unified interface. What do you think of it?
Regards, Zhi Yong Wu
Regards,
Zhi Yong Wu
Stefan
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