|
| From: | Avihai Horon |
| Subject: | Re: [PATCH v2 03/20] vfio/migration: Add VFIO migration pre-copy support |
| Date: | Thu, 23 Feb 2023 17:25:12 +0200 |
| User-agent: | Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 |
On 22/02/2023 22:58, Alex Williamson wrote:
External email: Use caution opening links or attachments On Wed, 22 Feb 2023 19:48:58 +0200 Avihai Horon <avihaih@nvidia.com> wrote:Pre-copy support allows the VFIO device data to be transferred while the VM is running. This helps to accommodate VFIO devices that have a large amount of data that needs to be transferred, and it can reduce migration downtime. Pre-copy support is optional in VFIO migration protocol v2. Implement pre-copy of VFIO migration protocol v2 and use it for devices that support it. Full description of it can be found here [1]. [1] https://lore.kernel.org/kvm/20221206083438.37807-3-yishaih@nvidia.com/ Signed-off-by: Avihai Horon <avihaih@nvidia.com> --- docs/devel/vfio-migration.rst | 35 +++++-- include/hw/vfio/vfio-common.h | 3 + hw/vfio/common.c | 6 +- hw/vfio/migration.c | 175 ++++++++++++++++++++++++++++++++-- hw/vfio/trace-events | 4 +- 5 files changed, 201 insertions(+), 22 deletions(-) diff --git a/docs/devel/vfio-migration.rst b/docs/devel/vfio-migration.rst index c214c73e28..ba80b9150d 100644 --- a/docs/devel/vfio-migration.rst +++ b/docs/devel/vfio-migration.rst @@ -7,12 +7,14 @@ the guest is running on source host and restoring this saved state on the destination host. This document details how saving and restoring of VFIO devices is done in QEMU. -Migration of VFIO devices currently consists of a single stop-and-copy phase. -During the stop-and-copy phase the guest is stopped and the entire VFIO device -data is transferred to the destination. - -The pre-copy phase of migration is currently not supported for VFIO devices. -Support for VFIO pre-copy will be added later on. +Migration of VFIO devices consists of two phases: the optional pre-copy phase, +and the stop-and-copy phase. The pre-copy phase is iterative and allows to +accommodate VFIO devices that have a large amount of data that needs to be +transferred. The iterative pre-copy phase of migration allows for the guest to +continue whilst the VFIO device state is transferred to the destination, this +helps to reduce the total downtime of the VM. VFIO devices can choose to skip +the pre-copy phase of migration by not reporting the VFIO_MIGRATION_PRE_COPY +flag in VFIO_DEVICE_FEATURE_MIGRATION ioctl.Or alternatively for the last sentence, VFIO devices opt-in to pre-copy support by reporting the VFIO_MIGRATION_PRE_COPY flag in the VFIO_DEVICE_FEATURE_MIGRATION ioctl.
Sounds good, I will change it.
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 @@ -29,10 +31,20 @@ VFIO implements the device hooks for the iterative approach as follows: * A ``load_setup`` function that sets the VFIO device on the destination in _RESUMING state. +* A ``state_pending_estimate`` function that reports an estimate of the + remaining pre-copy data that the vendor driver has yet to save for the VFIO + device. + * A ``state_pending_exact`` function that reads pending_bytes from the vendor driver, which indicates the amount of data that the vendor driver has yet to save for the VFIO device. +* An ``is_active_iterate`` function that indicates ``save_live_iterate`` is + active only when the VFIO device is in pre-copy states. + +* A ``save_live_iterate`` function that reads the VFIO device's data from the + vendor driver during iterative pre-copy phase. + * 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 @@ -95,8 +107,10 @@ Flow of state changes during Live migration =========================================== Below is the flow of state change during live migration. -The values in the brackets represent the VM state, the migration state, and +The values in the parentheses represent the VM state, the migration state, and the VFIO device state, respectively. +The text in the square brackets represents the flow if the VFIO device supports +pre-copy. Live migration save path ------------------------ @@ -108,11 +122,12 @@ Live migration save path | migrate_init spawns migration_thread Migration thread then calls each device's .save_setup() - (RUNNING, _SETUP, _RUNNING) + (RUNNING, _SETUP, _RUNNING [_PRE_COPY]) | - (RUNNING, _ACTIVE, _RUNNING) - If device is active, get pending_bytes by .state_pending_exact() + (RUNNING, _ACTIVE, _RUNNING [_PRE_COPY]) + If device is active, get pending_bytes by .state_pending_{estimate,exact}() If total pending_bytes >= threshold_size, call .save_live_iterate() + [Data of VFIO device for pre-copy phase is copied] Iterate till total pending bytes converge and are less than threshold | On migration completion, vCPU stops and calls .save_live_complete_precopy for diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h index 87524c64a4..ee55d442b4 100644 --- a/include/hw/vfio/vfio-common.h +++ b/include/hw/vfio/vfio-common.h @@ -66,6 +66,9 @@ typedef struct VFIOMigration { int data_fd; void *data_buffer; size_t data_buffer_size; + uint64_t precopy_init_size; + uint64_t precopy_dirty_size;size_t?+ uint64_t mig_flags; } VFIOMigration; typedef struct VFIOAddressSpace { diff --git a/hw/vfio/common.c b/hw/vfio/common.c index bab83c0e55..6f5afe9f5a 100644 --- a/hw/vfio/common.c +++ b/hw/vfio/common.c @@ -409,7 +409,8 @@ static bool vfio_devices_all_dirty_tracking(VFIOContainer *container) } if (vbasedev->pre_copy_dirty_page_tracking == ON_OFF_AUTO_OFF && - migration->device_state == VFIO_DEVICE_STATE_RUNNING) { + (migration->device_state == VFIO_DEVICE_STATE_RUNNING || + migration->device_state == VFIO_DEVICE_STATE_PRE_COPY)) { return false; } } @@ -438,7 +439,8 @@ static bool vfio_devices_all_running_and_mig_active(VFIOContainer *container) return false; } - if (migration->device_state == VFIO_DEVICE_STATE_RUNNING) { + if (migration->device_state == VFIO_DEVICE_STATE_RUNNING || + migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) { continue; } else { return false; diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c index 94a4df73d0..307983d57d 100644 --- a/hw/vfio/migration.c +++ b/hw/vfio/migration.c @@ -67,6 +67,8 @@ static const char *mig_state_to_str(enum vfio_device_mig_state state) return "STOP_COPY"; case VFIO_DEVICE_STATE_RESUMING: return "RESUMING"; + case VFIO_DEVICE_STATE_PRE_COPY: + return "PRE_COPY"; default: return "UNKNOWN STATE"; } @@ -240,6 +242,23 @@ static int vfio_query_stop_copy_size(VFIODevice *vbasedev, return 0; } +static int vfio_query_precopy_size(VFIOMigration *migration, + uint64_t *init_size, uint64_t *dirty_size)size_t? Seems like a concern throughout.
Yes, I will change it in all places.
+{ + struct vfio_precopy_info precopy = { + .argsz = sizeof(precopy), + }; + + if (ioctl(migration->data_fd, VFIO_MIG_GET_PRECOPY_INFO, &precopy)) { + return -errno; + } + + *init_size = precopy.initial_bytes; + *dirty_size = precopy.dirty_bytes; + + return 0; +} + /* Returns the size of saved data on success and -errno on error */ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration) { @@ -248,6 +267,11 @@ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration) data_size = read(migration->data_fd, migration->data_buffer, migration->data_buffer_size); if (data_size < 0) { + /* Pre-copy emptied all the device state for now */ + if (errno == ENOMSG) { + return 0; + } + return -errno; } if (data_size == 0) { @@ -264,6 +288,31 @@ static ssize_t vfio_save_block(QEMUFile *f, VFIOMigration *migration) return qemu_file_get_error(f) ?: data_size; } +static void vfio_update_estimated_pending_data(VFIOMigration *migration, + uint64_t data_size) +{ + if (!data_size) { + /* + * Pre-copy emptied all the device state for now, update estimated sizes + * accordingly. + */ + migration->precopy_init_size = 0; + migration->precopy_dirty_size = 0; + + return; + } + + if (migration->precopy_init_size) { + uint64_t init_size = MIN(migration->precopy_init_size, data_size); + + migration->precopy_init_size -= init_size; + data_size -= init_size; + } + + migration->precopy_dirty_size -= MIN(migration->precopy_dirty_size, + data_size); +} + /* ---------------------------------------------------------------------- */ static int vfio_save_setup(QEMUFile *f, void *opaque) @@ -284,6 +333,35 @@ static int vfio_save_setup(QEMUFile *f, void *opaque) return -ENOMEM; } + if (migration->mig_flags & VFIO_MIGRATION_PRE_COPY) { + uint64_t init_size = 0, dirty_size = 0; + int ret; + + switch (migration->device_state) { + case VFIO_DEVICE_STATE_RUNNING: + ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_PRE_COPY, + VFIO_DEVICE_STATE_RUNNING); + if (ret) { + return ret; + } + + vfio_query_precopy_size(migration, &init_size, &dirty_size); + migration->precopy_init_size = init_size; + migration->precopy_dirty_size = dirty_size;Seems like we could do away with {init,dirty}_size, initialize migration->precopy_{init,dirty}_size before the switch, pass them directly to vfio_query_precopy_size() and remove all but the break from the case below. But then that also suggests we could redefine vfio_query_precopy_size() to static int vfio_update_precopy_info(VFIOMigration *migration) which sets the fields directly since this is the only way it's used.
You are right, I will change it.
+ + break; + case VFIO_DEVICE_STATE_STOP: + /* vfio_save_complete_precopy() will go to STOP_COPY */ + + migration->precopy_init_size = 0; + migration->precopy_dirty_size = 0; + + break; + default: + return -EINVAL; + } + } + trace_vfio_save_setup(vbasedev->name, migration->data_buffer_size); qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE); @@ -302,23 +380,44 @@ static void vfio_save_cleanup(void *opaque) trace_vfio_save_cleanup(vbasedev->name); } +static void vfio_state_pending_estimate(void *opaque, uint64_t threshold_size, + uint64_t *must_precopy, + uint64_t *can_postcopy) +{ + VFIODevice *vbasedev = opaque; + VFIOMigration *migration = vbasedev->migration; + + if (migration->device_state != VFIO_DEVICE_STATE_PRE_COPY) { + return; + } + + /* + * Initial size should be transferred during pre-copy phase so stop-copy + * phase will not be slowed down. Report threshold_size to force another + * pre-copy iteration. + */ + *must_precopy += migration->precopy_init_size ? + threshold_size : + migration->precopy_dirty_size;This sure feels like we're feeding false data back to the iterator to spoof it to run another iteration, when the vfio migration protocol only recommends that initial_bytes reaches zero before proceeding to stop-copy, it's not a requirement. What benefit is actually observed from this? Why is this required for initial pre-copy support? It seems devious.
As previously discussed in the thread that added the pre-copy uAPI [1], the init_bytes can be used by drivers to reduce the downtime. For example, mlx5 transfers some metadata to the target so it will be able to pre-allocate resources etc.
[1] https://lore.kernel.org/kvm/ae4a6259-349d-0131-896c-7a6ea775cc9e@nvidia.com/
Thanks!
+ + trace_vfio_state_pending_estimate(vbasedev->name, *must_precopy, + *can_postcopy, + migration->precopy_init_size, + migration->precopy_dirty_size); +} + /* * Migration size of VFIO devices can be as little as a few KBs or as big as * many GBs. This value should be big enough to cover the worst case. */ #define VFIO_MIG_STOP_COPY_SIZE (100 * GiB) -/* - * Only exact function is implemented and not estimate function. The reason is - * that during pre-copy phase of migration the estimate function is called - * repeatedly while pending RAM size is over the threshold, thus migration - * can't converge and querying the VFIO device pending data size is useless. - */ static void vfio_state_pending_exact(void *opaque, uint64_t threshold_size, uint64_t *must_precopy, uint64_t *can_postcopy) { VFIODevice *vbasedev = opaque; + VFIOMigration *migration = vbasedev->migration; uint64_t stop_copy_size = VFIO_MIG_STOP_COPY_SIZE; /* @@ -328,8 +427,57 @@ static void vfio_state_pending_exact(void *opaque, uint64_t threshold_size, vfio_query_stop_copy_size(vbasedev, &stop_copy_size); *must_precopy += stop_copy_size; + if (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY) { + uint64_t init_size = 0, dirty_size = 0; + + vfio_query_precopy_size(migration, &init_size, &dirty_size); + migration->precopy_init_size = init_size; + migration->precopy_dirty_size = dirty_size;This is the only other caller of vfio_query_precopy_size(), following the same pattern that could be simplified if the function filled the migration fields itself.+ + /* + * Initial size should be transferred during pre-copy phase so + * stop-copy phase will not be slowed down. Report threshold_size + * to force another pre-copy iteration. + */ + *must_precopy += migration->precopy_init_size ? + threshold_size : + migration->precopy_dirty_size; + }Just as sketchy as above. Thanks, Alex+ trace_vfio_state_pending_exact(vbasedev->name, *must_precopy, *can_postcopy, - stop_copy_size); + stop_copy_size, migration->precopy_init_size, + migration->precopy_dirty_size); +} + +static bool vfio_is_active_iterate(void *opaque) +{ + VFIODevice *vbasedev = opaque; + VFIOMigration *migration = vbasedev->migration; + + return migration->device_state == VFIO_DEVICE_STATE_PRE_COPY; +} + +static int vfio_save_iterate(QEMUFile *f, void *opaque) +{ + VFIODevice *vbasedev = opaque; + VFIOMigration *migration = vbasedev->migration; + ssize_t data_size; + + data_size = vfio_save_block(f, migration); + 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); + + trace_vfio_save_iterate(vbasedev->name); + + /* + * A VFIO device's pre-copy dirty_bytes is not guaranteed to reach zero. + * Return 1 so following handlers will not be potentially blocked. + */ + return 1; } static int vfio_save_complete_precopy(QEMUFile *f, void *opaque) @@ -338,7 +486,7 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque) ssize_t data_size; int ret; - /* We reach here with device state STOP only */ + /* We reach here with device state STOP or STOP_COPY only */ ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY, VFIO_DEVICE_STATE_STOP); if (ret) { @@ -457,7 +605,10 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id) static const SaveVMHandlers savevm_vfio_handlers = { .save_setup = vfio_save_setup, .save_cleanup = vfio_save_cleanup, + .state_pending_estimate = vfio_state_pending_estimate, .state_pending_exact = vfio_state_pending_exact, + .is_active_iterate = vfio_is_active_iterate, + .save_live_iterate = vfio_save_iterate, .save_live_complete_precopy = vfio_save_complete_precopy, .save_state = vfio_save_state, .load_setup = vfio_load_setup, @@ -470,13 +621,18 @@ static const SaveVMHandlers savevm_vfio_handlers = { static void vfio_vmstate_change(void *opaque, bool running, RunState state) { VFIODevice *vbasedev = opaque; + VFIOMigration *migration = vbasedev->migration; enum vfio_device_mig_state new_state; int ret; if (running) { new_state = VFIO_DEVICE_STATE_RUNNING; } else { - new_state = VFIO_DEVICE_STATE_STOP; + new_state = + (migration->device_state == VFIO_DEVICE_STATE_PRE_COPY && + (state == RUN_STATE_FINISH_MIGRATE || state == RUN_STATE_PAUSED)) ? + VFIO_DEVICE_STATE_STOP_COPY : + VFIO_DEVICE_STATE_STOP; } /* @@ -590,6 +746,7 @@ static int vfio_migration_init(VFIODevice *vbasedev) migration->vbasedev = vbasedev; migration->device_state = VFIO_DEVICE_STATE_RUNNING; migration->data_fd = -1; + migration->mig_flags = mig_flags; oid = vmstate_if_get_id(VMSTATE_IF(DEVICE(obj))); if (oid) { diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events index 669d9fe07c..51613e02e6 100644 --- a/hw/vfio/trace-events +++ b/hw/vfio/trace-events @@ -161,6 +161,8 @@ vfio_save_block(const char *name, int data_size) " (%s) data_size %d" vfio_save_cleanup(const char *name) " (%s)" vfio_save_complete_precopy(const char *name, int ret) " (%s) ret %d" vfio_save_device_config_state(const char *name) " (%s)" +vfio_save_iterate(const char *name) " (%s)" vfio_save_setup(const char *name, uint64_t data_buffer_size) " (%s) data buffer size 0x%"PRIx64 -vfio_state_pending_exact(const char *name, uint64_t precopy, uint64_t postcopy, uint64_t stopcopy_size) " (%s) precopy 0x%"PRIx64" postcopy 0x%"PRIx64" stopcopy size 0x%"PRIx64 +vfio_state_pending_estimate(const char *name, uint64_t precopy, uint64_t postcopy, uint64_t precopy_init_size, uint64_t precopy_dirty_size) " (%s) precopy 0x%"PRIx64" postcopy 0x%"PRIx64" precopy initial size 0x%"PRIx64" precopy dirty size 0x%"PRIx64 +vfio_state_pending_exact(const char *name, uint64_t precopy, uint64_t postcopy, uint64_t stopcopy_size, uint64_t precopy_init_size, uint64_t precopy_dirty_size) " (%s) precopy 0x%"PRIx64" postcopy 0x%"PRIx64" stopcopy size 0x%"PRIx64" precopy initial size 0x%"PRIx64" precopy dirty size 0x%"PRIx64 vfio_vmstate_change(const char *name, int running, const char *reason, const char *dev_state) " (%s) running %d reason %s device state %s"
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