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migration: Add switchover ack capability

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Migration downtime estimation is calculated based on bandwidth and
remaining migration data. This assumes that loading of migration data in
the destination takes a negligible amount of time and that downtime
depends only on network speed.

While this may be true for RAM, it's not necessarily true for other
migrated devices. For example, loading the data of a VFIO device in the
destination might require from the device to allocate resources, prepare
internal data structures and so on. These operations can take a
significant amount of time which can increase migration downtime.

This patch adds a new capability "switchover ack" that prevents the
source from stopping the VM and completing the migration until an ACK
is received from the destination that it's OK to do so.

This can be used by migrated devices in various ways to reduce downtime.
For example, a device can send initial precopy metadata to pre-allocate
resources in the destination and use this capability to make sure that
the pre-allocation is completed before the source VM is stopped, so it
will have full effect.

This new capability relies on the return path capability to communicate
from the destination back to the source.

The actual implementation of the capability will be added in the
following patches.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Markus Armbruster <armbru@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>
This commit is contained in:
Avihai Horon
2023-06-21 14:11:54 +03:00
committed by Cédric Le Goater
parent 4d541f63e9
commit 6574232fff
3 changed files with 33 additions and 1 deletions
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21
migration/options.c
View File

@ -185,6 +185,8 @@ Property migration_properties[] = {
DEFINE_PROP_MIG_CAP("x-zero-copy-send",
MIGRATION_CAPABILITY_ZERO_COPY_SEND),
#endif
DEFINE_PROP_MIG_CAP("x-switchover-ack",
MIGRATION_CAPABILITY_SWITCHOVER_ACK),
DEFINE_PROP_END_OF_LIST(),
};
@ -308,6 +310,13 @@ bool migrate_return_path(void)
return s->capabilities[MIGRATION_CAPABILITY_RETURN_PATH];
}
bool migrate_switchover_ack(void)
{
MigrationState *s = migrate_get_current();
return s->capabilities[MIGRATION_CAPABILITY_SWITCHOVER_ACK];
}
bool migrate_validate_uuid(void)
{
MigrationState *s = migrate_get_current();
@ -547,6 +556,18 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
}
}
if (new_caps[MIGRATION_CAPABILITY_SWITCHOVER_ACK]) {
if (!new_caps[MIGRATION_CAPABILITY_RETURN_PATH]) {
error_setg(errp, "Capability 'switchover-ack' requires capability "
"'return-path'");
return false;
}
/* Disable this capability until it's implemented */
error_setg(errp, "'switchover-ack' is not implemented yet");
return false;
}
return true;
}