@@ -16,6 +16,13 @@ helps to reduce the total downtime of the VM. VFIO devices opt-in to pre-copy
support by reporting the VFIO_MIGRATION_PRE_COPY flag in the
VFIO_DEVICE_FEATURE_MIGRATION ioctl.
+When pre-copy is supported, it's possible to further reduce downtime by
+enabling "precopy-initial-data" migration capability.
+VFIO migration uAPI defines "initial bytes" as part of its pre-copy data stream
+and recommends that the initial bytes are sent and loaded in the destination
+before stopping the source VM. Enabling this migration capability will
+guarantee that and thus, can potentially reduce downtime even further.
+
Note that currently VFIO migration is supported only for a single device. This
is due to VFIO migration's lack of P2P support. However, P2P support is planned
to be added later on.
@@ -45,6 +52,9 @@ VFIO implements the device hooks for the iterative approach as follows:
* A ``save_live_iterate`` function that reads the VFIO device's data from the
vendor driver during iterative pre-copy phase.
+* An ``initial_data_advise`` function that advises the VFIO device to use
+ "precopy-initial-data" migration capability if supported.
+
* A ``save_state`` function to save the device config space if it is present.
* A ``save_live_complete_precopy`` function that sets the VFIO device in
@@ -69,6 +69,8 @@ typedef struct VFIOMigration {
uint64_t precopy_init_size;
uint64_t precopy_dirty_size;
uint64_t mig_flags;
+ bool initial_data_active;
+ bool initial_data_sent;
} VFIOMigration;
typedef struct VFIOAddressSpace {
@@ -18,6 +18,7 @@
#include "sysemu/runstate.h"
#include "hw/vfio/vfio-common.h"
#include "migration/migration.h"
+#include "migration/savevm.h"
#include "migration/vmstate.h"
#include "migration/qemu-file.h"
#include "migration/register.h"
@@ -45,6 +46,7 @@
#define VFIO_MIG_FLAG_DEV_CONFIG_STATE (0xffffffffef100002ULL)
#define VFIO_MIG_FLAG_DEV_SETUP_STATE (0xffffffffef100003ULL)
#define VFIO_MIG_FLAG_DEV_DATA_STATE (0xffffffffef100004ULL)
+#define VFIO_MIG_FLAG_DEV_INIT_DATA_SENT (0xffffffffef100005ULL)
/*
* This is an arbitrary size based on migration of mlx5 devices, where typically
@@ -380,6 +382,8 @@ static void vfio_save_cleanup(void *opaque)
g_free(migration->data_buffer);
migration->data_buffer = NULL;
+ migration->initial_data_sent = false;
+ migration->initial_data_active = false;
vfio_migration_cleanup(vbasedev);
trace_vfio_save_cleanup(vbasedev->name);
}
@@ -455,10 +459,17 @@ static int vfio_save_iterate(QEMUFile *f, void *opaque)
if (data_size < 0) {
return data_size;
}
- qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
vfio_update_estimated_pending_data(migration, data_size);
+ if (migration->initial_data_active && !migration->precopy_init_size &&
+ !migration->initial_data_sent) {
+ qemu_put_be64(f, VFIO_MIG_FLAG_DEV_INIT_DATA_SENT);
+ migration->initial_data_sent = true;
+ } else {
+ qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
+ }
+
trace_vfio_save_iterate(vbasedev->name);
/*
@@ -576,6 +587,24 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
}
break;
}
+ case VFIO_MIG_FLAG_DEV_INIT_DATA_SENT:
+ {
+ if (!vbasedev->migration->initial_data_active) {
+ error_report("%s: Received INIT_DATA_SENT but initial data is "
+ "not active",
+ vbasedev->name);
+ return -EINVAL;
+ }
+
+ ret = qemu_loadvm_notify_initial_data_loaded();
+ if (ret) {
+ error_report("%s: qemu_loadvm_notify_initial_data_loaded "
+ "failed, err=%d (%s)",
+ vbasedev->name, ret, strerror(-ret));
+ }
+
+ return ret;
+ }
default:
error_report("%s: Unknown tag 0x%"PRIx64, vbasedev->name, data);
return -EINVAL;
@@ -590,6 +619,16 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
return ret;
}
+static bool vfio_initial_data_advise(void *opaque)
+{
+ VFIODevice *vbasedev = opaque;
+ VFIOMigration *migration = vbasedev->migration;
+
+ migration->initial_data_active = vfio_precopy_supported(vbasedev);
+
+ return migration->initial_data_active;
+}
+
static const SaveVMHandlers savevm_vfio_handlers = {
.save_setup = vfio_save_setup,
.save_cleanup = vfio_save_cleanup,
@@ -602,6 +641,7 @@ static const SaveVMHandlers savevm_vfio_handlers = {
.load_setup = vfio_load_setup,
.load_cleanup = vfio_load_cleanup,
.load_state = vfio_load_state,
+ .initial_data_advise = vfio_initial_data_advise,
};
/* ---------------------------------------------------------------------- */
Loading of a VFIO device's data can take a substantial amount of time as the device may need to allocate resources, prepare internal data structures, etc. This can increase migration downtime, especially for VFIO devices with a lot of resources. To solve this, VFIO migration uAPI defines "initial bytes" as part of its precopy data stream. Initial bytes can be used in various ways to improve VFIO migration performance. For example, it can be used to transfer device metadata to pre-allocate resources in the destination. However, for this to work we need to make sure that all initial bytes are sent and loaded in the destination before the source VM is stopped. Use migration precopy initial data capability to make sure a VFIO device's initial bytes are sent and loaded in the destination before the source stops the VM and attempts to complete the migration. This can significantly reduce migration downtime for some devices. As precopy support and precopy initial data support come together in VFIO migration, use x-allow-pre-copy device property to control usage of this feature as well. Signed-off-by: Avihai Horon <avihaih@nvidia.com> --- docs/devel/vfio-migration.rst | 10 +++++++++ include/hw/vfio/vfio-common.h | 2 ++ hw/vfio/migration.c | 42 ++++++++++++++++++++++++++++++++++- 3 files changed, 53 insertions(+), 1 deletion(-)