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

On Thu, Sep 01, 2011 at 09:11:49AM +0100, Stefan Hajnoczi wrote: >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. QEMU I/O throttling currently don't support those options of blkiotune, such as --live, --config and --current.If those bps/iops settings are modified, it will immediately take effect.