[v3] vhost-user-blk: support inflight migration

[PATCH v3 0/3] vhost-user-blk: support inflight migration

Alexandr Moshkov posted 3 patches 4 days, 4 hours ago

Diff against v1 v2
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Failed in applying to current master (apply log)

hw/block/vhost-user-blk.c          | 29 +++++++++++++++++++++
hw/virtio/vhost.c                  | 42 ++++++++++++++++++++++++++++++
include/hw/virtio/vhost-user-blk.h |  1 +
include/hw/virtio/vhost.h          |  6 +++++
include/migration/vmstate.h        | 10 +++++++
5 files changed, 88 insertions(+)

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[PATCH v3 0/3] vhost-user-blk: support inflight migration

Posted by Alexandr Moshkov 4 days, 4 hours ago

v3:
- use pre_load_errp instead of pre_load in vhost.c
- change vhost-user-blk property to
  "skip-get-vring-base-inflight-migration"
- refactor vhost-user-blk.c, by moving vhost_user_blk_inflight_needed() higher

v2:
- rewrite migration using VMSD instead of qemufile API
- add vhost-user-blk parameter instead of migration capability

I don't know if VMSD was used cleanly in migration implementation, so
feel free for comments.

Based on Vladimir's work:
[PATCH v2 00/25] vhost-user-blk: live-backend local migration
  which was based on:
    - [PATCH v4 0/7] chardev: postpone connect
      (which in turn is based on [PATCH 0/2] remove deprecated 'reconnect' options)
    - [PATCH v3 00/23] vhost refactoring and fixes
    - [PATCH v8 14/19] migration: introduce .pre_incoming() vmsd handler

Based-on: <20250924133309.334631-1-vsementsov@yandex-team.ru>
Based-on: <20251015212051.1156334-1-vsementsov@yandex-team.ru>
Based-on: <20251015145808.1112843-1-vsementsov@yandex-team.ru>
Based-on: <20251015132136.1083972-15-vsementsov@yandex-team.ru>
Based-on: <20251016114104.1384675-1-vsementsov@yandex-team.ru>

--- 

Hi!

During inter-host migration, waiting for disk requests to be drained
in the vhost-user backend can incur significant downtime.

This can be avoided if QEMU migrates the inflight region in vhost-user-blk. 
Thus, during the qemu migration, the vhost-user backend can cancel all inflight requests and
then, after migration, they will be executed on another host. 

At first, I tried to implement migration for all vhost-user devices that support inflight at once, 
but this would require a lot of changes both in vhost-user-blk (to transfer it to the base class) and 
in the vhost-user-base base class (inflight implementation and remodeling + a large refactor).

Therefore, for now I decided to leave this idea for later and 
implement the migration of the inflight region first for vhost-user-blk.

Alexandr Moshkov (3):
  vmstate: introduce VMSTATE_VBUFFER_UINT64
  vhost: add vmstate for inflight region with inner buffer
  vhost-user-blk: support inter-host inflight migration

 hw/block/vhost-user-blk.c          | 29 +++++++++++++++++++++
 hw/virtio/vhost.c                  | 42 ++++++++++++++++++++++++++++++
 include/hw/virtio/vhost-user-blk.h |  1 +
 include/hw/virtio/vhost.h          |  6 +++++
 include/migration/vmstate.h        | 10 +++++++
 5 files changed, 88 insertions(+)

-- 
2.34.1