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| author | Avihai Horon <avihaih@nvidia.com> | 2023-06-21 14:12:01 +0300 |
|---|---|---|
| committer | Cédric Le Goater <clg@redhat.com> | 2023-06-30 06:02:51 +0200 |
| commit | 745c42912a04306e8c7765dd4cc1574a92de4446 (patch) | |
| tree | 9ee82cef34ab44292802318abe938ca7f4ad0ac9 /docs/devel | |
| parent | eda7362af9595a9c6b1f1fefdd94b5ef711c250c (diff) | |
| download | qemu-745c42912a04306e8c7765dd4cc1574a92de4446.zip qemu-745c42912a04306e8c7765dd4cc1574a92de4446.tar.gz qemu-745c42912a04306e8c7765dd4cc1574a92de4446.tar.bz2 | |
vfio/migration: Add support for switchover ack capability
Loading of a VFIO device's data can take a substantial amount of time as
the device may need to allocate resources, prepare internal data
structures, etc. This can increase migration downtime, especially for
VFIO devices with a lot of resources.
To solve this, VFIO migration uAPI defines "initial bytes" as part of
its precopy data stream. Initial bytes can be used in various ways to
improve VFIO migration performance. For example, it can be used to
transfer device metadata to pre-allocate resources in the destination.
However, for this to work we need to make sure that all initial bytes
are sent and loaded in the destination before the source VM is stopped.
Use migration switchover ack capability to make sure a VFIO device's
initial bytes are sent and loaded in the destination before the source
stops the VM and attempts to complete the migration.
This can significantly reduce migration downtime for some devices.
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Tested-by: YangHang Liu <yanghliu@redhat.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Diffstat (limited to 'docs/devel')
| -rw-r--r-- | docs/devel/vfio-migration.rst | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/docs/devel/vfio-migration.rst b/docs/devel/vfio-migration.rst index e896b2a..b433cb5 100644 --- a/docs/devel/vfio-migration.rst +++ b/docs/devel/vfio-migration.rst @@ -16,6 +16,13 @@ helps to reduce the total downtime of the VM. VFIO devices opt-in to pre-copy support by reporting the VFIO_MIGRATION_PRE_COPY flag in the VFIO_DEVICE_FEATURE_MIGRATION ioctl. +When pre-copy is supported, it's possible to further reduce downtime by +enabling "switchover-ack" migration capability. +VFIO migration uAPI defines "initial bytes" as part of its pre-copy data stream +and recommends that the initial bytes are sent and loaded in the destination +before stopping the source VM. Enabling this migration capability will +guarantee that and thus, can potentially reduce downtime even further. + Note that currently VFIO migration is supported only for a single device. This is due to VFIO migration's lack of P2P support. However, P2P support is planned to be added later on. @@ -45,6 +52,9 @@ VFIO implements the device hooks for the iterative approach as follows: * A ``save_live_iterate`` function that reads the VFIO device's data from the vendor driver during iterative pre-copy phase. +* A ``switchover_ack_needed`` function that checks if the VFIO device uses + "switchover-ack" migration capability when this capability is enabled. + * A ``save_state`` function to save the device config space if it is present. * A ``save_live_complete_precopy`` function that sets the VFIO device in |