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[Qemu-devel] [PATCH v2 00/25] dataplane: use QEMU block layer

From: Stefan Hajnoczi
Subject: [Qemu-devel] [PATCH v2 00/25] dataplane: use QEMU block layer
Date: Wed, 7 May 2014 12:27:16 +0200

 * Currently unaddressed: libiscsi nop timer re-entrancy, is it a problem? 
[Peter Lieven]
 * Protect bdrv_*_all() with AioContext acquire/release [Christian Borntraeger]
 * Convert raw-win32 and aio-win32 [Paolo]
 * Rebase on latest curl.c changes [Fam]
 * Add curl_attach_aio_context() assert since it shouldn't be called twice [Fam]
 * Drop curl comment that doesn't make sense in the new code [Fam]
 * Replace g_slice_new()+memset() with g_slice_new0() in dataplane/virtio-blk.c 

This patch series switches virtio-blk data-plane from a custom Linux AIO
request queue to the QEMU block layer.  The previous "raw files only"
limitation is lifted.  All image formats and protocols can now be used with
virtio-blk data-plane.

How to review this series
I CCed the maintainer of each block driver that I modified.  You probably don't
need to review the entire series, just your patch.

>From now on fd handlers, timers, BHs, and event loop wait must explicitly use
BlockDriverState's AioContext instead of the main loop.  Use
bdrv_get_aio_context(bs) to get the AioContext.  The following function calls
need to be converted:

 * qemu_aio_set_fd_handler() -> aio_set_fd_handler()
 * timer_new*() -> aio_timer_new()
 * qemu_bh_new() -> aio_bh_new()
 * qemu_aio_wait() -> aio_poll(aio_context, true)

For simple block drivers this modification suffices and it is now safe to use
outside the QEMU global mutex.

Block drivers that keep fd handlers, timers, or BHs registered when requests
have been drained need a little bit more work.  Examples of this are network
block drivers with keepalive timers, like iSCSI.

This series adds a new bdrv_set_aio_context(bs, aio_context) function that
moves a BlockDriverState into a new AioContext.  This function calls the block
driver's optional .bdrv_detach_aio_context() and .bdrv_attach_aio_context()
functions.  Implement detach/attach to move the fd handlers, timers, or BHs to
the new AioContext.

Finally, block drivers that manage their own child nodes also need to
implement detach/attach because the generic block layer doesn't know about
their children.  Both ->file and ->backing_hd are automatically taken care of
but blkverify, quorum, and VMDK need to manually propagate detach/attach to
their children.

I have audited and modified all block drivers.  Block driver maintainers,
please check I did it correctly and didn't break your code.

The block layer is currently tied to the QEMU main loop for fd handlers, timer
callbacks, and BHs.  This means that even on hosts with many cores, parts of
block I/O processing happen in one thread and depend on the QEMU global mutex.

virtio-blk data-plane has shown that 1,000,000 IOPS is achievable if we use
additional threads that are not under the QEMU global mutex.

It is necessary to make the QEMU block layer aware that there may be more than
one event loop.  This way BlockDriverState can be used from a thread without
contention on the QEMU global mutex.

This series builds on the aio_context_acquire/release() interface that allows a
thread to temporarily grab an AioContext.  We add bdrv_set_aio_context(bs,
aio_context) for changing which AioContext a BlockDriverState uses.

The final patches convert virtio-blk data-plane to use the QEMU block layer and
let the BlockDriverState run in the IOThread AioContext.

What's next?
I have already made block I/O throttling work in another AioContext and will
send the series out next week.

In order to keep this series reviewable, I'm holding back those patches for
now.  One could say, "throttling" them.

Thank you, thank you, I'll be here all night!

Stefan Hajnoczi (25):
  block: use BlockDriverState AioContext
  block: acquire AioContext in bdrv_*_all()
  block: acquire AioContext in bdrv_drain_all()
  block: add bdrv_set_aio_context()
  blkdebug: use BlockDriverState's AioContext
  blkverify: implement .bdrv_detach/attach_aio_context()
  curl: implement .bdrv_detach/attach_aio_context()
  gluster: use BlockDriverState's AioContext
  iscsi: implement .bdrv_detach/attach_aio_context()
  nbd: implement .bdrv_detach/attach_aio_context()
  nfs: implement .bdrv_detach/attach_aio_context()
  qed: use BlockDriverState's AioContext
  quorum: implement .bdrv_detach/attach_aio_context()
  block/raw-posix: implement .bdrv_detach/attach_aio_context()
  block/linux-aio: fix memory and fd leak
  block/raw-win32: create one QEMUWin32AIOState per BDRVRawState
  block/raw-win32: implement .bdrv_detach/attach_aio_context()
  rbd: use BlockDriverState's AioContext
  sheepdog: implement .bdrv_detach/attach_aio_context()
  ssh: use BlockDriverState's AioContext
  vmdk: implement .bdrv_detach/attach_aio_context()
  dataplane: use the QEMU block layer for I/O
  dataplane: delete IOQueue since it is no longer used
  dataplane: implement async flush
  raw-posix: drop raw_get_aio_fd() since it is no longer used

 block.c                          | 133 +++++++++++++++++-----
 block/blkdebug.c                 |   2 +-
 block/blkverify.c                |  47 +++++---
 block/curl.c                     | 192 +++++++++++++++++++-------------
 block/gluster.c                  |   7 +-
 block/iscsi.c                    |  79 +++++++++----
 block/linux-aio.c                |  24 +++-
 block/nbd-client.c               |  24 +++-
 block/nbd-client.h               |   4 +
 block/nbd.c                      |  87 +++++++++------
 block/nfs.c                      |  80 ++++++++++----
 block/qed-table.c                |   8 +-
 block/qed.c                      |  35 +++++-
 block/quorum.c                   |  48 ++++++--
 block/raw-aio.h                  |   8 ++
 block/raw-posix.c                |  82 ++++++++------
 block/raw-win32.c                |  54 ++++++---
 block/rbd.c                      |   5 +-
 block/sheepdog.c                 | 118 +++++++++++++-------
 block/ssh.c                      |  36 +++---
 block/vmdk.c                     |  23 ++++
 block/win32-aio.c                |  23 +++-
 hw/block/dataplane/Makefile.objs |   2 +-
 hw/block/dataplane/ioq.c         | 117 --------------------
 hw/block/dataplane/ioq.h         |  57 ----------
 hw/block/dataplane/virtio-blk.c  | 232 +++++++++++++++------------------------
 include/block/block.h            |  20 ++--
 include/block/block_int.h        |  36 ++++++
 28 files changed, 923 insertions(+), 660 deletions(-)
 delete mode 100644 hw/block/dataplane/ioq.c
 delete mode 100644 hw/block/dataplane/ioq.h


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