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vfio/migration: Add x-migration-multifd-transfer VFIO property

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This property allows configuring whether to transfer the particular device
state via multifd channels when live migrating that device.

It defaults to AUTO, which means that VFIO device state transfer via
multifd channels is attempted in configurations that otherwise support it.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/d6dbb326e3d53c7104d62c96c9e3dd64e1c7b940.1741124640.git.maciej.szmigiero@oracle.com
[ clg: Added documentation ]
Signed-off-by: Cédric Le Goater <clg@redhat.com>
This commit is contained in:
Maciej S. Szmigiero 2025-03-04 23:03:58 +01:00 • committed by Cédric Le Goater
parent 6d644baef2
commit 623af41dd3
4 changed files with 41 additions and 1 deletions
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15
docs/devel/migration/vfio.rst
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@ -232,3 +232,18 @@ Postcopy
========
Postcopy migration is currently not supported for VFIO devices.
Multifd
=======
Starting from QEMU version 10.0 there's a possibility to transfer VFIO device
_STOP_COPY state via multifd channels. This helps reduce downtime - especially
with multiple VFIO devices or with devices having a large migration state.
As an additional benefit, setting the VFIO device to _STOP_COPY state and
saving its config space is also parallelized (run in a separate thread) in
such migration mode.
The multifd VFIO device state transfer is controlled by
"x-migration-multifd-transfer" VFIO device property. This property defaults to
AUTO, which means that VFIO device state transfer via multifd channels is
attempted in configurations that otherwise support it.