[libvirt] The design choice for how to enable block I/O throttling function in libvirt

[Stefan Hajnoczi]

On Tue, Aug 30, 2011 at 3:55 AM, Zhi Yong Wu <zwu.kernel at 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.

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.

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

Stefan