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

From: "Daniel P. Berrange" <berrange(a)redhat.com&gt; To: Stefan Hajnoczi <stefanha(a)gmail.com&gt; Cc: Zhi Yong Wu <wuzhy(a)linux.vnet.ibm.com&gt;, libvir-list(a)redhat.com, agl(a)us.ibm.com, qemu-devel(a)nongnu.org, guijianfeng(a)cn.fujitsu.com, hutao(a)cn.fujitsu.com, zwu.kernel(a)gmail.com Subject: Re: [RFC] block I/O throttling: how to enable in libvirt Message-ID: <20110901084934.GA14462(a)redhat.com&gt; Reply-To: "Daniel P. Berrange" <berrange(a)redhat.com&gt; References: <20110901050531.GB17963(a)f15.cn.ibm.com&gt; <20110901081149.GB14245(a)stefanha-thinkpad.localdomain&gt; MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20110901081149.GB14245(a)stefanha-thinkpad.localdomain&gt; 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(a)redhat.com X-Xagent-To: wuzhy(a)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(a)us.ibm.com&gt; 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-i... > > >> > > >> 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.

Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|