[Qemu-devel] [PATCH RFC 0/3] iothread: release iothread around aio_poll

[Paolo Bonzini <pbonzini@redhat.com>]

Right now, iothreads are relying on a "contention callback" to release
the AioContext (e.g. for block device operations or to do bdrv_drain_all).
This is necessary because aio_poll needs to be called within an
aio_context_acquire.

This series drops this requirement for aio_poll, with two effects:

1) it makes it possible to remove the "contention callback" in RFifoLock
(and possibly to convert it to a normal GRecMutex, which is why I am not
including a patch to remove callbacks from RFifoLock).

2) it makes it possible to start work around making critical sections
for the block layer fine-grained.

In order to do this, some data is moved from AioContext to local storage.
Stack allocation has size limitations, so thread-local storage is used
instead.  There are no reentrancy problems because the data is only live
throughout a small part of aio_poll, and in particular not during the
invocation of callbacks.

Comments?

Paolo

Paolo Bonzini (3):
  aio-posix: move pollfds to thread-local storage
  AioContext: acquire/release AioContext during aio_poll
  iothread: release iothread around aio_poll

 aio-posix.c         | 86 ++++++++++++++++++++++++++++++++++++++++-------------
 aio-win32.c         |  8 +++++
 async.c             | 10 +------
 include/block/aio.h | 18 +++++------
 iothread.c          | 11 ++-----
 tests/test-aio.c    | 21 +++++++------
 6 files changed, 96 insertions(+), 58 deletions(-)

-- 
2.3.0