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

Date: Thu, 1 Sep 2011 09:11:49 +0100 From: Stefan Hajnoczi <stefanha(a)gmail.com&gt; To: Zhi Yong Wu <wuzhy(a)linux.vnet.ibm.com&gt; Message-ID: <20110901081149.GB14245(a)stefanha-thinkpad.localdomain&gt; References: <20110901050531.GB17963(a)f15.cn.ibm.com&gt; MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20110901050531.GB17963(a)f15.cn.ibm.com&gt; User-Agent: Mutt/1.5.21 (2010-09-15) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 2) X-Received-From: 74.125.82.173 Cc: libvir-list(a)redhat.com, guijianfeng(a)cn.fujitsu.com, agl(a)us.ibm.com, qemu-devel(a)nongnu.org, zwu.kernel(a)gmail.com, hutao(a)cn.fujitsu.com Subject: Re: [Qemu-devel] [RFC] block I/O throttling: how to enable in libvirt X-BeenThere: qemu-devel(a)nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: <qemu-devel.nongnu.org> List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>;, <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe> List-Archive: </archive/html/qemu-devel> List-Post: <mailto:qemu-devel@nongnu.org> List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help> List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>;, <mailto:qemu-devel-request@nongnu.org?subject=subscribe> X-Mailman-Copy: yes Errors-To: qemu-devel-bounces+wuzhy=linux.vnet.ibm.com(a)nongnu.org Sender: qemu-devel-bounces+wuzhy=linux.vnet.ibm.com(a)nongnu.org x-cbid: 11090108-7282-0000-0000-0000010970B0 X-IBM-ISS-SpamDetectors: Score=0; BY=0; FL=0; FP=0; FZ=0; HX=0; KW=0; PH=0; SC=0; ST=0; TS=0; UL=0; ISC= X-IBM-ISS-DetailInfo: BY=3.00000211; HX=3.00000168; KW=3.00000007; PH=3.00000001; SC=3.00000001; SDB=6.00067104; UDB=6.00020326; UTC=2011-09-01 08:12:15 X-Xagent-From: stefanha(a)gmail.com X-Xagent-To: wuzhy(a)linux.vnet.ibm.com X-Xagent-Gateway: vmsdvm6.vnet.ibm.com (XAGENTU5 at VMSDVM6) 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.

Stefan