Re: [PATCH v4 00/33] Multifd 🔀 device state transfer support with VFIO consumer

[Fabiano Rosas <farosas@suse.de>]

"Maciej S. Szmigiero" <mail@maciej.szmigiero.name> writes:

> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>
> This is an updated v4 patch series of the v3 series located here:
> https://lore.kernel.org/qemu-devel/cover.1731773021.git.maciej.szmigiero@oracle.com/
>
> Changes from v3:
> * MigrationLoadThread now returns bool and an Error complex error type
> instead of just an int.
>
> * qemu_loadvm_load_thread_pool now reports error via migrate_set_error()
> instead of dedicated load_threads_ret variable.
>
> * Since the change above uncovered an issue with respect to multifd send
> channels not terminating TLS session properly QIOChannelTLS now allows
> gracefully handling this situation.
>
> * qemu_loadvm_load_thread_pool state is now part of MigrationIncomingState
> instead of being stored in global variables.
> This state now also has its own init/cleanup helpers.
>
> * qemu_loadvm_load_thread_pool code is now moved into a separate section
> of the savevm.c file, marked by an appropriate comment.
>
> * thread_pool_free() is now documented to have wait-before-free semantic,
> which allowed removal of explicit waits from thread pool cleanup paths.
>
> * thread_pool_submit_immediate() method was added since this functionality
> is used by both generic thread pool users in this patch set.
>
> * postcopy_ram_listen_thread() now takes BQL around function calls that
> ultimately call migration methods requiring BQL.
> This fixes one of QEMU tests failing when explicitly BQL-sensitive code
> is added later to these methods.
>
> * qemu_loadvm_load_state_buffer() now returns a bool value instead of int.
>
> * "Send final SYNC only after device state is complete" patch was
> dropped since Peter implemented equivalent functionality upstream.
>
> * "Document the BQL behavior of load SaveVMHandlers" patch was dropped
> since that's something better done later, separately from this patch set.
>
> * Header size is now added to mig_stats.multifd_bytes where it is actually
> sent in the zero copy case - in multifd_nocomp_send_prepare().
>
> * Spurious wakeups from qemu_cond_wait() are now handled properly as
> pointed out by Avihai.
>
> * VFIO migration FD now allows partial write() completion as pointed out
> by Avihai.
>
> * Patch "vfio/migration: Don't run load cleanup if load setup didn't run"
> was dropped, instead all objects related to multifd load are now located in
> their own VFIOMultifd struct which is allocated only if multifd device state
> transfer is actually in use.
>
> * Intermediate VFIOStateBuffers API as suggested by Avihai is now introduced
> to simplify vfio_load_state_buffer() and vfio_load_bufs_thread().
>
> * Optional VFIO device config state loading interlocking with loading
> other iterables is now possible due to ARM64 platform VFIO dependency on
> interrupt controller being loaded first as pointed out by Avihai.
>
> * Patch "Multifd device state transfer support - receive side" was split
> into a few smaller patches as suggested by Cédric.
>
> * x-migration-multifd-transfer VFIO property compat changes were moved
> into a separate patch as suggested by Cédric.
>
> * Other small changes, like renamed functions and variables/members, added
> review tags, code formatting, moved QEMU_LOCK_GUARD() instances closer to
> actual protected blocks, etc.
>
> ========================================================================
>
> This patch set is targeting QEMU 10.0.
>
> What's not yet present is documentation update under docs/devel/migration
> but I didn't want to delay posting the code any longer.
> Such doc can still be merged later when the design is 100% finalized.
>
> ========================================================================
>
> Maciej S. Szmigiero (32):
>   migration: Clarify that {load,save}_cleanup handlers can run without
>     setup
>   thread-pool: Remove thread_pool_submit() function
>   thread-pool: Rename AIO pool functions to *_aio() and data types to
>     *Aio
>   thread-pool: Implement generic (non-AIO) pool support
>   migration: Add MIG_CMD_SWITCHOVER_START and its load handler
>   migration: Add qemu_loadvm_load_state_buffer() and its handler
>   io: tls: Allow terminating the TLS session gracefully with EOF
>   migration/multifd: Allow premature EOF on TLS incoming channels
>   migration: postcopy_ram_listen_thread() needs to take BQL for some
>     calls
>   error: define g_autoptr() cleanup function for the Error type
>   migration: Add thread pool of optional load threads
>   migration/multifd: Split packet into header and RAM data
>   migration/multifd: Device state transfer support - receive side
>   migration/multifd: Make multifd_send() thread safe
>   migration/multifd: Add an explicit MultiFDSendData destructor
>   migration/multifd: Device state transfer support - send side
>   migration/multifd: Add multifd_device_state_supported()
>   migration: Add save_live_complete_precopy_thread handler
>   vfio/migration: Add x-migration-load-config-after-iter VFIO property
>   vfio/migration: Add load_device_config_state_start trace event
>   vfio/migration: Convert bytes_transferred counter to atomic
>   vfio/migration: Multifd device state transfer support - basic types
>   vfio/migration: Multifd device state transfer support -
>     VFIOStateBuffer(s)
>   vfio/migration: Multifd device state transfer - add support checking
>     function
>   vfio/migration: Multifd device state transfer support - receive
>     init/cleanup
>   vfio/migration: Multifd device state transfer support - received
>     buffers queuing
>   vfio/migration: Multifd device state transfer support - load thread
>   vfio/migration: Multifd device state transfer support - config loading
>     support
>   migration/qemu-file: Define g_autoptr() cleanup function for QEMUFile
>   vfio/migration: Multifd device state transfer support - send side
>   vfio/migration: Add x-migration-multifd-transfer VFIO property
>   hw/core/machine: Add compat for x-migration-multifd-transfer VFIO
>     property
>
> Peter Xu (1):
>   migration/multifd: Make MultiFDSendData a struct
>
>  hw/core/machine.c                  |   2 +
>  hw/vfio/migration.c                | 754 ++++++++++++++++++++++++++++-
>  hw/vfio/pci.c                      |  14 +
>  hw/vfio/trace-events               |  11 +-
>  include/block/aio.h                |   8 +-
>  include/block/thread-pool.h        |  62 ++-
>  include/hw/vfio/vfio-common.h      |   7 +
>  include/io/channel-tls.h           |  11 +
>  include/migration/client-options.h |   4 +
>  include/migration/misc.h           |  16 +
>  include/migration/register.h       |  54 ++-
>  include/qapi/error.h               |   2 +
>  include/qemu/typedefs.h            |   6 +
>  io/channel-tls.c                   |   6 +
>  migration/colo.c                   |   3 +
>  migration/meson.build              |   1 +
>  migration/migration-hmp-cmds.c     |   2 +
>  migration/migration.c              |   6 +-
>  migration/migration.h              |   7 +
>  migration/multifd-device-state.c   | 192 ++++++++
>  migration/multifd-nocomp.c         |  30 +-
>  migration/multifd.c                | 248 ++++++++--
>  migration/multifd.h                |  74 ++-
>  migration/options.c                |   9 +
>  migration/qemu-file.h              |   2 +
>  migration/savevm.c                 | 195 +++++++-
>  migration/savevm.h                 |   6 +-
>  migration/trace-events             |   1 +
>  scripts/analyze-migration.py       |  11 +
>  tests/unit/test-thread-pool.c      |   6 +-
>  util/async.c                       |   6 +-
>  util/thread-pool.c                 | 184 +++++--
>  util/trace-events                  |   6 +-
>  33 files changed, 1814 insertions(+), 132 deletions(-)
>  create mode 100644 migration/multifd-device-state.c

Hi!

We have build issues:

https://gitlab.com/farosas/qemu/-/pipelines/1649146958

And the postcopy/recovery test is failing. It seems the migration
finishes before the test can issue migrate-pause:

QTEST_QEMU_BINARY=./qemu-system-x86_64  ./tests/qtest/migration-test -p
/x86_64/migration/postcopy/recovery/plain
...
{"execute": "migrate-start-postcopy"}
{"return": {}}
{"secs": 1738267018, "usecs": 860991}, "event": "MIGRATION", "data": {"status": "postcopy-active"}
{"secs": 1738267018, "usecs": 861284}, "event": "STOP"
{"secs": 1738267017, "usecs": 960322}, "event": "MIGRATION", "data": {"status": "active"}
{"secs": 1738267018, "usecs": 865589}, "event": "MIGRATION", "data": {"status": "postcopy-active"}
{"secs": 1738267099, "usecs": 120971}, "event": "MIGRATION", "data": {"status": "completed"}
{"secs": 1738267099, "usecs": 121154}, "event": "RESUME"
{"execute": "query-migrate"}

ERROR:../tests/qtest/migration/migration-qmp.c:172:check_migration_status:
assertion failed (current_status != "completed"): ("completed" !=
"completed")