KVM: Add io driver option to libvirt XML for io_uring support #4883
Description
ISSUE TYPE
- Feature Idea
COMPONENT NAME
KVM
CLOUDSTACK VERSION
master
SUMMARY
ouring is a new kernel asynchronous I/O processing mechanism proposed as a much faster alternative for conventional Linux AIO. Patches were merged in Linux 5.1 and gave a promised performance boost. We decided to integrate it into QEMU to make virtualized storage devices work more efficiently. Let's take a look at how iouring works in QEMU.
Source:
- https://www.phoronix.com/scan.php?page=news_item&px=KVM-IO-uring-Passthrough-LF2020
- https://archive.fosdem.org/2020/schedule/event/vai_io_uring_in_qemu/
By using io_uring with Qemu we can see a massive I/O performance improvement within Virtual Machines running from Local and/or NFS storage.
In order to use this we need:
- Qemu >= 5.0
- Libvirt >= 6.3.0
We then need to add this to the XML definition for libvirt which would then look like:
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2' cache='writeback' discard='unmap' io='io_uring'/>
<source file='/var/lib/libvirt/images/a0f677c6-b065-4795-b468-2b5974496c75'/>
<backingStore/>
<target dev='sda' bus='scsi'/>
<serial>a0f677c6b0654795b468</serial>
<alias name='scsi0-0-0-0'/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</disk>
With io_uring I/O performance can improve drastically and reach near bare-metal performance.
Currently there is no Qemu version in a stable Ubuntu nor CentOS release, but we can already merge this in master so that when this is released we can use it.