[0/8] virtio-blk: removal of AioContext lock

Message

Emanuele Giuseppe Esposito June 9, 2022, 2:37 p.m. UTC

This serie aims to free virtio-blk (and in the future all
virtio devices) from the AioContext lock.

First step is to understand which functions are running in
the main loop and which are in iothreads.
Because many functions in virtio-blk are callbacks called
in some other virtio (pci, mmio, bus and so on) callbacks,
this is not trivial.
Patches 4-5-6 aim to split at least virtio-blk API.

There are two main things to consider when comparing this serie
with the block layer API split:

- sometimes we have data that is accessed by both IO and GS
  functions, but never together. For example, when the main
  loop access some data, iothread is guaranteed to be stopped.

- taking into account the multiqueue setup:
  this work aims to allow an iothread to access multiple
  virtio queues, while assigning the same queue to only one
  iothread. Currently, we have a single iothread running,
  so if we know that the main loop is not interfering, we
  are safe. However, if we want to consider multiple iothreads
  concurrently running, we need to take additional precautions.

A good example of the above is in patch 7.

Signed-off-by: Emanuele Giuseppe Esposito <[e-mail]>

Emanuele Giuseppe Esposito (8):
  virtio_queue_aio_attach_host_notifier: remove AioContext lock
  block-backend: enable_write_cache should be atomic
  virtio_blk_process_queued_requests: always run in a bh
  virtio: categorize callbacks in GS
  virtio-blk: mark GLOBAL_STATE_CODE functions
  virtio-blk: mark IO_CODE functions
  VirtIOBlock: protect rq with its own lock
  virtio-blk: remove unnecessary AioContext lock from function already
    safe

 block/block-backend.c           |   6 +-
 hw/block/dataplane/virtio-blk.c |  32 +++++++-
 hw/block/virtio-blk.c           | 132 ++++++++++++++++++++++++--------
 hw/scsi/virtio-scsi-dataplane.c |  12 ++-
 hw/virtio/virtio-bus.c          |   5 ++
 hw/virtio/virtio-pci.c          |   2 +
 hw/virtio/virtio.c              |   8 ++
 include/hw/virtio/virtio-blk.h  |   6 +-
 8 files changed, 163 insertions(+), 40 deletions(-)