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1cc7737f69
Add plumbing for QEMU's switchover-ack migration capability, which helps lower the downtime during VFIO migrations. This capability is enabled by default as long as both the source and destination support it. Note: switchover-ack depends on the return path capability, so this may not be used when VIR_MIGRATE_TUNNELLED flag is set. Extensive details about the qemu switchover-ack implementation are available in the qemu series v6 cover letter [1] where the highlight is the extreme reduction in guest visible downtime. In addition to the original test results below, I saw a roughly ~20% reduction in downtime for VFIO VGPU devices at minimum. === Test results === The below table shows the downtime of two identical migrations. In the first migration swithcover ack is disabled and in the second it is enabled. The migrated VM is assigned with a mlx5 VFIO device which has 300MB of device data to be migrated. +----------------------+-----------------------+----------+ | Switchover ack | VFIO device data size | Downtime | +----------------------+-----------------------+----------+ | Disabled | 300MB | 1900ms | | Enabled | 300MB | 420ms | +----------------------+-----------------------+----------+ Switchover ack gives a roughly 4.5 times improvement in downtime. The 1480ms difference is time that is used for resource allocation for the VFIO device in the destination. Without switchover ack, this time is spent when the source VM is stopped and thus the downtime is much higher. With switchover ack, the time is spent when the source VM is still running. [1] https://patchwork.kernel.org/project/qemu-devel/cover/20230621111201.29729-1-avihaih@nvidia.com/ Signed-off-by: Jon Kohler <jon@nutanix.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Avihai Horon <avihaih@nvidia.com> Cc: Markus Armbruster <armbru@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: YangHang Liu <yanghliu@redhat.com> Reviewed-by: Jiri Denemark <jdenemar@redhat.com> |
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==============================
Libvirt API for virtualization
==============================
Libvirt provides a portable, long term stable C API for managing the
virtualization technologies provided by many operating systems. It
includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware
vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER
Hypervisor.
For some of these hypervisors, it provides a stateful management
daemon which runs on the virtualization host allowing access to the
API both by non-privileged local users and remote users.
Layered packages provide bindings of the libvirt C API into other
languages including Python, Perl, PHP, Go, Java, OCaml, as well as
mappings into object systems such as GObject, CIM and SNMP.
Further information about the libvirt project can be found on the
website:
https://libvirt.org
License
=======
The libvirt C API is distributed under the terms of GNU Lesser General
Public License, version 2.1 (or later). Some parts of the code that are
not part of the C library may have the more restrictive GNU General
Public License, version 2.0 (or later). See the files ``COPYING.LESSER``
and ``COPYING`` for full license terms & conditions.
Installation
============
Instructions on building and installing libvirt can be found on the website:
https://libvirt.org/compiling.html
Contributing
============
The libvirt project welcomes contributions in many ways. For most components
the best way to contribute is to send patches to the primary development
mailing list. Further guidance on this can be found on the website:
https://libvirt.org/contribute.html
Contact
=======
The libvirt project has two primary mailing lists:
* users@lists.libvirt.org (**for user discussions**)
* devel@lists.libvirt.org (**for development only**)
Further details on contacting the project are available on the website:
https://libvirt.org/contact.html