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Re: [PATCH v5 1/9] migration: Add switchover ack capability
From: |
YangHang Liu |
Subject: |
Re: [PATCH v5 1/9] migration: Add switchover ack capability |
Date: |
Thu, 15 Jun 2023 20:38:22 +0800 |
Test in the following two scenarios:
[1] Test scenario: Both source VM and target VM (in listening mode)
have enabled return-path and switchover-ack capability:
Test result : The VFIO migration completed successfully
[2] Test scenario : The source VM has enabled return-path and
switchover-ack capability while the target VM (in listening mode) not
Test result : The VFIO migration fails
The detailed error thrown by qemu-kvm when VFIO migration fails:
Target VM:
0000:17:00.2: Received INIT_DATA_SENT but switchover ack is not used
error while loading state section id 81(0000:00:02.4:00.0/vfio)
load of migration failed: Invalid argument
Source VM:
failed to save SaveStateEntry with id(name): 2(ram): -5
Unable to write to socket: Connection reset by peer
Unable to write to socket: Connection reset by peer
Tested-by: YangHang Liu <yanghliu@redhat.com>
On Wed, May 31, 2023 at 1:46 AM Avihai Horon <avihaih@nvidia.com> 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
> 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>
> ---
> qapi/migration.json | 12 +++++++++++-
> migration/options.h | 1 +
> migration/options.c | 21 +++++++++++++++++++++
> 3 files changed, 33 insertions(+), 1 deletion(-)
>
> 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;
> }
>
> --
> 2.26.3
>
>
- Re: [PATCH v5 1/9] migration: Add switchover ack capability,
YangHang Liu <=