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(a)gmail.com&gt; 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.

> 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?