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

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.