[Qemu-devel] [PATCH 0/5] threadpool: support multiple ThreadPools

[Stefan Hajnoczi]

This patch series changes the global thread pool to a one ThreadPool per
AioContext model.  We still only use the main loop AioContext so in practice
there is just one ThreadPool.  But this opens the door to refactoring the block
layer (which depends on ThreadPool) so block devices can be accessed outside
the global mutex in the future.

ThreadPool is tightly bound to an AioContext because it uses an EventNotifier
to signal work completion.  Completed work items are reaped and their callback
functions are invoked from the EventNotifier read handler (executing under
AioContext).

It might be possible to record the AioContext for the completion callback on a
per-request basis and continuing to use a global pool of worker threads.  After
discussing thread pool models with Paolo I have been convinced that it is
simpler and more scalable to have one ThreadPool per AioContext instead.
Therefore this series implements the 1:1 approach.  For details on previous
thread pool model discussion, see:
http://lists.gnu.org/archive/html/qemu-devel/2013-02/msg03987.html

At the end of this series block/raw-posix.c and block/raw-win32.c are aware of
the ThreadPool they submit work to.  The next step after this series is to
associate BlockDriverState with an AioContext so that the block layer can run
outside the global main loop.

Stefan Hajnoczi (5):
  threadpool: move globals into struct ThreadPool
  threadpool: add thread_pool_new() and thread_pool_free()
  aio: add a ThreadPool instance to AioContext
  main-loop: add qemu_get_aio_context()
  threadpool: drop global thread pool

 async.c                     |  11 ++
 block/raw-posix.c           |   8 +-
 block/raw-win32.c           |   4 +-
 include/block/aio.h         |   6 ++
 include/block/thread-pool.h |  15 ++-
 include/qemu/main-loop.h    |   5 +
 main-loop.c                 |   5 +
 tests/test-thread-pool.c    |  44 ++++----
 thread-pool.c               | 252 ++++++++++++++++++++++++++++----------------
 trace-events                |   4 +-
 10 files changed, 233 insertions(+), 121 deletions(-)

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1.8.1.4