| Message ID | 20230521151808.24804-2-avihaih@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | migration: Add switchover ack capability and VFIO precopy support | expand |
On Sun, May 21, 2023 at 06:18:02PM +0300, Avihai Horon wrote: > 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 > migration users. 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>
Avihai Horon <avihaih@nvidia.com> writes: > 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 > migration users. 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> QAPI schema Acked-by: Markus Armbruster <armbru@redhat.com>
diff --git a/qapi/migration.json b/qapi/migration.json index 179af0c4d8..061ea512e0 100644 --- a/qapi/migration.json +++ b/qapi/migration.json @@ -487,6 +487,16 @@ # and should not affect the correctness of postcopy migration. # (since 7.1) # +# @switchover-ack: If enabled, migration will not stop the source VM +# and complete the migration until an ACK is received from the +# destination that it's OK to do so. Exactly when this ACK is +# sent depends on the migrated devices that use this feature. +# For example, a device can use it to make sure some of its data +# is sent and loaded in the destination before doing switchover. +# This can reduce downtime if devices that support this capability +# are present. 'return-path' capability must be enabled to use +# it. (since 8.1) +# # Features: # # @unstable: Members @x-colo and @x-ignore-shared are experimental. @@ -502,7 +512,7 @@ 'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate', { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] }, 'validate-uuid', 'background-snapshot', - 'zero-copy-send', 'postcopy-preempt'] } + 'zero-copy-send', 'postcopy-preempt', 'switchover-ack'] } ## # @MigrationCapabilityStatus: diff --git a/migration/options.h b/migration/options.h index 45991af3c2..9aaf363322 100644 --- a/migration/options.h +++ b/migration/options.h @@ -40,6 +40,7 @@ bool migrate_postcopy_ram(void); bool migrate_rdma_pin_all(void); bool migrate_release_ram(void); bool migrate_return_path(void); +bool migrate_switchover_ack(void); bool migrate_validate_uuid(void); bool migrate_xbzrle(void); bool migrate_zero_blocks(void); diff --git a/migration/options.c b/migration/options.c index b62ab30cd5..16007afca6 100644 --- a/migration/options.c +++ b/migration/options.c @@ -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; }
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 migration users. 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> --- qapi/migration.json | 12 +++++++++++- migration/options.h | 1 + migration/options.c | 21 +++++++++++++++++++++ 3 files changed, 33 insertions(+), 1 deletion(-)