[Qemu-devel] [PATCH 0/6] block: do request processing in a coroutine

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

Block layer features like dirty block tracing, I/O throttling, and live block
copy are forced to duplicate code due to the three different interfaces:
synchronous, asynchronous, and coroutines.

Since there are bdrv_read(), bdrv_aio_readv(), and bdrv_co_readv() interfaces
for read (and similar for write), per-request processing needs to be duplicated
for each of these execution contexts.  For example, dirty block tracking code
is duplicated across these three interfaces.

This patch series unifies request processing so that there is only one code
path.  I see this as a prerequisite to the live block copy (image streaming)
code I am working on, so I'm pushing it now.

The short-term win from this series is that it becomes easy to add live block
copy and other features.  We now have a single code path where the perf-request
processing is done.

The longer-term win will be dropping the BlockDriver .bdrv_read(),
.bdrv_write(), .bdrv_aio_readv(), and .bdrv_aio_writev() interfaces.  By doing
that we can bring all BlockDrivers onto a common interface, namely
.bdrv_co_readv() and .bdrv_co_writev().  It will also allow us to drop most of
the sync and aio emulation code.

A consequence of this patch series is that every I/O request goes through at
least one coroutine.  There is no longer a direct .bdrv_read(), .bdrv_write(),
.bdrv_aio_readv(), or .bdrv_aio_writev() call - we're trying to phase out those
interfaces.  I have not noticed performance degradation in correctness tests
but we need to confirm that there has not been a performance regression.

Stefan Hajnoczi (6):
  block: directly invoke .bdrv_aio_*() in bdrv_co_io_em()
  block: split out bdrv_co_do_readv() and bdrv_co_do_writev()
  block: switch bdrv_read()/bdrv_write() to coroutines
  block: switch bdrv_aio_readv() to coroutines
  block: mark blocks dirty on coroutine write completion
  block: switch bdrv_aio_writev() to coroutines

 block.c |  273 +++++++++++++++++++++++++++++++--------------------------------
 1 files changed, 134 insertions(+), 139 deletions(-)

-- 
1.7.6.3