[Openstack-operators] Setting IOthreads on a Nova Instance

George Shuklin george.shuklin at gmail.com
Fri Jun 12 18:53:19 UTC 2015

Ceph is slow as a hell by itself, and qemu/libvirt/nova adds qcow2 on 
top of that.

Try to run it with raw volumes, at least. And check if you have properly 
configured network (jumbo frames, no overloaded switch tables, etc).

On 06/12/2015 09:49 AM, pushpesh sharma wrote:
> Hi list,
> I need some expert opinion on some problem I am facing with
> OpenStack+Ceph environment.
> I running a 3+ node cluster with OpenStack Juno. It is using ceph RBDs
> as cinder volumes. Functionally setup is working fine. However my
> expectation are related to block performance of RBDs inside a VM.
> I am observing a throttling effect in 100%- 4K RR iops after a point.
> Lots of CPU
> cycles got wasted in iowait. I suspect a single iothread per VM is
> causing this.I came to know about few tuning parameter that libvirt
> provides. It looks pretty straight forward to set these parameter
> in domain xml . However I am not able to do so. I didn't find any way
> to pass these
> parameter form nova directly, and when I edit domain.xml directly
> using 'virsh edit' the changes vanish even after saving the xml
> properly.(I know it is not a clean way to this, but a hack)
> It could be validation problem:-
> ############
> #virsh dumpxml instance-000000c5 > vm.xml
> #virt-xml-validate vm.xml
> Relax-NG validity error : Extra element cpu in interleave
> vm.xml:1: element domain: Relax-NG validity error : Element domain
> failed to validate content
> vm.xml fails to validate
> ##################
> Second approach I took was to setting QoS in volumes types. But there
> is no option to set iothreads per volume, there are parameters related
> to max_read/wrirte ops/bytes.
> Thirdly, editing Nova flavor and proving extra specs like
> hw:cpu_socket/thread/core, can change guest CPU topology however again
> no way to set iothread. It does accept hw_disk_iothreads(no type check
> in place, i believe ), but can not pass the same in domain.xml.
> Please suggest me a way to set the same.

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