[libvirt] [PATCH v2 02/15] Add public APIs for post-copy migration
Daniel P. Berrange
berrange at redhat.com
Fri Jan 22 15:10:16 UTC 2016
On Thu, Jan 21, 2016 at 11:20:47AM +0100, Jiri Denemark wrote:
> From: Cristian Klein <cristiklein at gmail.com>
>
> To use post-copy one has to start the migration with
> VIR_MIGRATE_POSTCOPY flag and, while migration is in progress, call
> virDomainMigrateStartPostCopy() to switch from pre-copy to post-copy.
>
> Signed-off-by: Cristian Klein <cristiklein at gmail.com>
> Signed-off-by: Jiri Denemark <jdenemar at redhat.com>
> ---
>
> Notes:
> Version 2:
> - POSTCOPY_AFTER_PRECOPY flag removed
>
> include/libvirt/libvirt-domain.h | 4 ++
> src/driver-hypervisor.h | 5 ++
> src/libvirt-domain.c | 114 +++++++++++++++++++++++++++++++++++++++
> src/libvirt_public.syms | 4 ++
> src/remote/remote_driver.c | 1 +
> src/remote/remote_protocol.x | 13 ++++-
> src/remote_protocol-structs | 5 ++
> 7 files changed, 145 insertions(+), 1 deletion(-)
>
> diff --git a/include/libvirt/libvirt-domain.h b/include/libvirt/libvirt-domain.h
> index 50342d2..ccbf6a7 100644
> --- a/include/libvirt/libvirt-domain.h
> +++ b/include/libvirt/libvirt-domain.h
> @@ -662,6 +662,7 @@ typedef enum {
> VIR_MIGRATE_ABORT_ON_ERROR = (1 << 12), /* abort migration on I/O errors happened during migration */
> VIR_MIGRATE_AUTO_CONVERGE = (1 << 13), /* force convergence */
> VIR_MIGRATE_RDMA_PIN_ALL = (1 << 14), /* RDMA memory pinning */
> + VIR_MIGRATE_POSTCOPY = (1 << 15), /* enable (but do not start) post-copy migration */
> } virDomainMigrateFlags;
>
>
> @@ -810,6 +811,9 @@ int virDomainMigrateGetMaxSpeed(virDomainPtr domain,
> unsigned long *bandwidth,
> unsigned int flags);
>
> +int virDomainMigrateStartPostCopy(virDomainPtr domain,
> + unsigned int flags);
> +
> char * virConnectGetDomainCapabilities(virConnectPtr conn,
> const char *emulatorbin,
> const char *arch,
> diff --git a/src/driver-hypervisor.h b/src/driver-hypervisor.h
> index ae2ec4d..68a7730 100644
> --- a/src/driver-hypervisor.h
> +++ b/src/driver-hypervisor.h
> @@ -638,6 +638,10 @@ typedef int
> const char *dom_xml);
>
> typedef int
> +(*virDrvDomainMigrateStartPostCopy)(virDomainPtr domain,
> + unsigned int flags);
> +
> +typedef int
> (*virDrvConnectIsEncrypted)(virConnectPtr conn);
>
> typedef int
> @@ -1443,6 +1447,7 @@ struct _virHypervisorDriver {
> virDrvDomainGetFSInfo domainGetFSInfo;
> virDrvDomainInterfaceAddresses domainInterfaceAddresses;
> virDrvDomainSetUserPassword domainSetUserPassword;
> + virDrvDomainMigrateStartPostCopy domainMigrateStartPostCopy;
> };
>
>
> diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c
> index 9491845..676f0f7 100644
> --- a/src/libvirt-domain.c
> +++ b/src/libvirt-domain.c
> @@ -3537,6 +3537,7 @@ virDomainMigrateUnmanaged(virDomainPtr domain,
> * automatically when supported).
> * VIR_MIGRATE_UNSAFE Force migration even if it is considered unsafe.
> * VIR_MIGRATE_OFFLINE Migrate offline
> + * VIR_MIGRATE_POSTCOPY Enable (but do not start) post-copy
> *
> * VIR_MIGRATE_TUNNELLED requires that VIR_MIGRATE_PEER2PEER be set.
> * Applications using the VIR_MIGRATE_PEER2PEER flag will probably
> @@ -3573,6 +3574,11 @@ virDomainMigrateUnmanaged(virDomainPtr domain,
> * not support this feature and will return an error if bandwidth
> * is not 0.
> *
> + * Enabling the VIR_MIGRATE_POSTCOPY flag tells libvirt to enable post-copy
> + * migration. Use virDomainMigrateStartPostCopy to switch migration into
> + * the post-copy mode. See virDomainMigrateStartPostCopy for more details
> + * about post-copy.
> + *
> * To see which features are supported by the current hypervisor,
> * see virConnectGetCapabilities, /capabilities/host/migration_features.
> *
> @@ -3748,6 +3754,7 @@ virDomainMigrate(virDomainPtr domain,
> * automatically when supported).
> * VIR_MIGRATE_UNSAFE Force migration even if it is considered unsafe.
> * VIR_MIGRATE_OFFLINE Migrate offline
> + * VIR_MIGRATE_POSTCOPY Enable (but do not start) post-copy
> *
> * VIR_MIGRATE_TUNNELLED requires that VIR_MIGRATE_PEER2PEER be set.
> * Applications using the VIR_MIGRATE_PEER2PEER flag will probably
> @@ -3784,6 +3791,11 @@ virDomainMigrate(virDomainPtr domain,
> * not support this feature and will return an error if bandwidth
> * is not 0.
> *
> + * Enabling the VIR_MIGRATE_POSTCOPY flag tells libvirt to enable post-copy
> + * migration. Use virDomainMigrateStartPostCopy to switch migration into
> + * the post-copy mode. See virDomainMigrateStartPostCopy for more details
> + * about post-copy.
> + *
> * To see which features are supported by the current hypervisor,
> * see virConnectGetCapabilities, /capabilities/host/migration_features.
> *
> @@ -3968,6 +3980,11 @@ virDomainMigrate2(virDomainPtr domain,
> * can use either VIR_MIGRATE_NON_SHARED_DISK or
> * VIR_MIGRATE_NON_SHARED_INC as they are mutually exclusive.
> *
> + * Enabling the VIR_MIGRATE_POSTCOPY flag tells libvirt to enable post-copy
> + * migration. Use virDomainMigrateStartPostCopy to switch migration into
> + * the post-copy mode. See virDomainMigrateStartPostCopy for more details
> + * about post-copy.
> + *
> * There are many limitations on migration imposed by the underlying
> * technology - for example it may not be possible to migrate between
> * different processors even with the same architecture, or between
> @@ -4208,6 +4225,7 @@ int virDomainMigrateUnmanagedCheckCompat(virDomainPtr domain,
> * automatically when supported).
> * VIR_MIGRATE_UNSAFE Force migration even if it is considered unsafe.
> * VIR_MIGRATE_OFFLINE Migrate offline
> + * VIR_MIGRATE_POSTCOPY Enable (but do not start) post-copy
> *
> * The operation of this API hinges on the VIR_MIGRATE_PEER2PEER flag.
> * If the VIR_MIGRATE_PEER2PEER flag is NOT set, the duri parameter
> @@ -4240,6 +4258,11 @@ int virDomainMigrateUnmanagedCheckCompat(virDomainPtr domain,
> * not support this feature and will return an error if bandwidth
> * is not 0.
> *
> + * Enabling the VIR_MIGRATE_POSTCOPY flag tells libvirt to enable post-copy
> + * migration. Use virDomainMigrateStartPostCopy to switch migration into
> + * the post-copy mode. See virDomainMigrateStartPostCopy for more details
> + * about post-copy.
> + *
> * To see which features are supported by the current hypervisor,
> * see virConnectGetCapabilities, /capabilities/host/migration_features.
> *
> @@ -4321,6 +4344,7 @@ virDomainMigrateToURI(virDomainPtr domain,
> * automatically when supported).
> * VIR_MIGRATE_UNSAFE Force migration even if it is considered unsafe.
> * VIR_MIGRATE_OFFLINE Migrate offline
> + * VIR_MIGRATE_POSTCOPY Enable (but do not start) post-copy
> *
> * The operation of this API hinges on the VIR_MIGRATE_PEER2PEER flag.
> *
> @@ -4366,6 +4390,11 @@ virDomainMigrateToURI(virDomainPtr domain,
> * not support this feature and will return an error if bandwidth
> * is not 0.
> *
> + * Enabling the VIR_MIGRATE_POSTCOPY flag tells libvirt to enable post-copy
> + * migration. Use virDomainMigrateStartPostCopy to switch migration into
> + * the post-copy mode. See virDomainMigrateStartPostCopy for more details
> + * about post-copy.
> + *
> * To see which features are supported by the current hypervisor,
> * see virConnectGetCapabilities, /capabilities/host/migration_features.
> *
> @@ -4446,6 +4475,11 @@ virDomainMigrateToURI2(virDomainPtr domain,
> * can use either VIR_MIGRATE_NON_SHARED_DISK or
> * VIR_MIGRATE_NON_SHARED_INC as they are mutually exclusive.
> *
> + * Enabling the VIR_MIGRATE_POSTCOPY flag tells libvirt to enable post-copy
> + * migration. Use virDomainMigrateStartPostCopy to switch migration into
> + * the post-copy mode. See virDomainMigrateStartPostCopy for more details
> + * about post-copy.
> + *
> * There are many limitations on migration imposed by the underlying
> * technology - for example it may not be possible to migrate between
> * different processors even with the same architecture, or between
> @@ -9163,6 +9197,86 @@ virDomainMigrateGetMaxSpeed(virDomainPtr domain,
>
>
> /**
> + * virDomainMigrateStartPostCopy:
> + * @domain: a domain object
> + * @flags: extra flags; not used yet, so callers should always pass 0
> + *
> + * Starts post-copy migration. This function has to be called while
> + * migration (initiated with VIR_MIGRATE_POSTCOPY flag) is in progress.
> + *
> + * Traditional post-copy migration iteratively walks through guest memory
> + * pages and migrates those that changed since the previous iteration. The
> + * iterative phase stops when the number of dirty pages is low enough so that
> + * the virtual CPUs can be paused, all dirty pages transferred to the
> + * destination, where the virtual CPUs are unpaused, and all this can happen
> + * within a predefined downtime period. It's clear that this process may never
> + * converge if downtime is too short and/or the guest keeps changing a lot of
> + * memory pages.
> + *
> + * When migration is switched to post-copy mode, the virtual CPUs are paused
> + * immediately, only a minimum set of pages is transferred, and the CPUs are
> + * unpaused on destination. The source keeps sending all remaining memory pages
> + * to the destination while the guest is already running there. Whenever the
> + * guest tries to read a memory page which has not been migrated yet, the
> + * hypervisor has to tell the source to transfer that page in a priority
> + * channel. To minimize such page faults, it is a good idea to run at least one
> + * iteration of pre-copy migration before switching to post-copy.
> + *
> + * Post-copy migration is guaranteed to converge since each page is transferred
> + * at most once no matter how fast it changes. On the other hand once the
> + * guest is running on the destination host, the migration can no longer be
> + * rolled back because none of the hosts has complete state. If this happens,
> + * libvirt will leave the domain paused on both hosts with
> + * VIR_DOMAIN_PAUSED_POSTCOPY_FAILED reason. It's up to the upper layer to
> + * decide what to do in such case.
> + *
> + * The following domain life cycle events are emitted during post-copy
> + * migration:
> + * VIR_DOMAIN_EVENT_SUSPENDED_POSTCOPY (on the source) -- migration entered
> + * post-copy mode.
> + * VIR_DOMAIN_EVENT_RESUMED_POSTCOPY (on the destination) -- the guest is
> + * running on the destination host while some of its memory pages still
> + * remain on the source host; neither the source nor the destination host
> + * contain a complete guest state from this point until migration
> + * finishes.
> + * VIR_DOMAIN_EVENT_RESUMED_MIGRATED (on the destination),
> + * VIR_DOMAIN_EVENT_STOPPED_MIGRATED (on the source) -- migration finished
> + * successfully and the destination host holds a complete guest state.
> + * VIR_DOMAIN_EVENT_SUSPENDED_POSTCOPY_FAILED (on either side) -- emitted
> + * when migration fails in post-copy mode and it's unclear whether any
> + * of the hosts has a complete guest state.
You say either side, but IMHO issuing a suspended event when we are already
in a suspended state is not correct, as the VM is not undergoing a lifecycle
change in that scenario - you're essentially just using the reason field as
a way to report failure which I don't think we should really do.
So IMHO POSTCOPY_FAILED is only something to emit on the target.
The domain job on the source will show the migration failure in any
case, so I don't think its important on the source
Regards,
Daniel
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