[Qemu-devel] [PATCH v4 00/20] block: Asynchronous request cancellation

[Fam Zheng <famz@redhat.com>]

v4: Drop AIOCBInfo.cancel.

This series adds a new block layer API:

  void bdrv_aio_cancel_async(BlockDriverAIOCB *acb);

And use it to emulate bdrv_aio_cancel.

The function is similar to bdrv_aio_cancel in that it cancels an AIO request,
but different that it doesn't block until the request is completely cancelled
or done.

More importantly, the completion callback, BlockDriverAIOCB.cb, is guaranteed
to be called, so that the cb can take care of resource releasing and status
reporting to guest, etc.

In the following work, scsi emulation code will be shifted to use the async
cancelling.

One major benefit would be that when guest tries to cancel a request, where the
request cannot be cancelled easily, (due to throttled BlockDriverState, a lost
connection, or a large request queue), we don't need to block the whole vm with
a busy loop, which is how bdrv_aio_cancel is implemented now.

A test case that is easy to reproduce is, throttle a scsi-disk to a very low
limit, for example 50 bps, then stress the guest block device with dd or fio.

Currently, the vm will quickly hang when it loses patience and send a tmf
command to cancel the request, at which point we will busy wait in
bdrv_aio_cancel, until the request is slowly spit out from throttled_reqs.

Later, we will change scsi device code to make this asynchronous, on top of
bdrv_aio_cancel_async.

Fam

Fam Zheng (20):
  block: Add refcnt in BlockDriverAIOCB
  block: Add bdrv_aio_cancel_async
  block: Drop bdrv_em_co_aiocb_info.cancel
  block: Convert bdrv_em_aiocb_info.cancel to .cancel_async
  thread-pool: Convert thread_pool_aiocb_info.cancel to cancel_async
  linux-aio: Convert laio_aiocb_info.cancel to .cancel_async
  dma: Check iov pointer before unmap memory
  dma: Convert dma_aiocb_info.cancel to .cancel_async
  iscsi: Convert iscsi_aiocb_info.cancel to .cancel_async
  archipelago: Drop archipelago_aiocb_info.cancel
  blkdebug: Convert blkdebug_aiocb_info.cancel to .cancel_async
  blkverify: Drop blkverify_aiocb_info.cancel
  curl: Drop curl_aiocb_info.cancel
  qed: Drop qed_aiocb_info.cancel
  quorum: Convert quorum_aiocb_info.cancel to .cancel_async
  rbd: Drop rbd_aiocb_info.cancel
  sheepdog: Convert sd_aiocb_info.cancel to .cancel_async
  win32-aio: Drop win32_aiocb_info.cancel
  ide: Convert trim_aiocb_info.cancel to .cancel_async
  block: Drop AIOCBInfo.cancel

 block.c                  | 61 +++++++++++++++++++++++++++++-------------------
 block/archipelago.c      | 17 +-------------
 block/blkdebug.c         |  6 +++--
 block/blkverify.c        | 19 ---------------
 block/curl.c             |  6 -----
 block/iscsi.c            | 17 ++------------
 block/linux-aio.c        | 30 +++++++-----------------
 block/qed.c              | 21 -----------------
 block/quorum.c           |  7 ++----
 block/rbd.c              | 23 +-----------------
 block/sheepdog.c         | 46 +++++++++++++++---------------------
 block/win32-aio.c        | 14 -----------
 dma-helpers.c            | 23 ++++++------------
 hw/ide/core.c            | 12 ++++------
 include/block/aio.h      |  5 +++-
 include/block/block.h    |  1 +
 tests/test-thread-pool.c | 34 ++++++++++++++++++++-------
 thread-pool.c            | 32 +++++++++++--------------
 18 files changed, 131 insertions(+), 243 deletions(-)

-- 
2.1.0.27.g96db324