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 <stefa...@gmail.com> >To: Adam Litke <a...@us.ibm.com> >Cc: libvir-l...@redhat.com, "Daniel P. Berrange" <berra...@redhat.com>, Zhi > Yong Wu <wu...@linux.vnet.ibm.com>, Zhi Yong Wu <zwu.ker...@gmail.com> >Content-Type: text/plain; charset=ISO-8859-1 >Content-Transfer-Encoding: quoted-printable >X-Brightmail-Tracker: AAAAAA== >X-Xagent-From: stefa...@gmail.com >X-Xagent-To: wu...@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 <a...@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.ker...@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-throttling-in-qemu.pdf >> >> 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. Danial and other maintainers, If you are available, can you make some comments for us?:) Regards, Zhi Yong Wu > >Stefan
