[Qemu-devel] [PATCH 00/30] Memory API changes for 1.6: RCU-protected address space dispatch

[Paolo Bonzini <pbonzini@redhat.com>]

These are the next part in the unlocked address space dispatch work.
At the end of this series, address space dispatch runs under an RCU
critical section (RCU is hopefully well documented in patch 8).
It becomes then possible to add unlocked variants of address_space_rw.

Compared to Liu Ping Fan's approach posted last year, the path I followed
is more long-winded but requires much less changes in device models that
choose to adopt lockless MMIO dispatching.  This is nice, because it
produces an API that is easier to use.

In addition, I decided to sidestep complicated locking discussions by
using RCU.  RCU can bulk-protect the read side of all data structures
while remaining extremely light-weight.  The write side needs its own
lock, but in many cases it can simply be the BQL (very useful for things
that perform updates in callbacks!).

Patches 1-3 add reference counting to FlatView, which is independent
from the other patches but a necessary prerequisite to protect
as->current_map with RCU.

Patches 4-17 implement RCU and update existing threads to be RCU-friendly
(again, more information is in docs/rcu.txt) whenever necessary.
A lot of the code here comes from the URCU library.

Patches 18-30 do the rest of the work, using fresh copies of the dispatch
data structures on every update.  Several patches in this series are
based on Liu Ping Fan's work, which I made more fine-grained.

The diffstat looks daunting; however, note that ~50% of the new lines
are documentation and test cases.  Available from branch rcu of my
github repository.

I don't plan to send a pull request for this series anytime soon,
but reviews and testing are welcome.

Paolo

Liu Ping Fan (1):
  exec: change well-known physical sections to macros

Paolo Bonzini (29):
  memory: access FlatView from a local variable
  memory: use a new FlatView pointer on every topology update
  memory: add reference counting to FlatView
  add a header file for atomic operations
  exec: do not use qemu/tls.h
  qemu-thread: add TLS wrappers
  qemu-thread: add QemuEvent
  rcu: add rcu library
  qemu-thread: register threads with RCU
  rcu: add call_rcu
  rcu: add rcutorture
  rcu: allow nested calls to rcu_thread_offline/rcu_thread_online
  qemu-thread: report RCU quiescent states
  event loop: report RCU quiescent states
  cpus: report RCU quiescent states
  block: report RCU quiescent states
  migration: report RCU quiescent states
  memory: protect current_map by RCU
  memory: avoid ref/unref in memory_region_find
  exec: separate current memory map from the one being built
  memory: move MemoryListener declaration earlier
  exec: move listener from AddressSpaceDispatch to AddressSpace
  exec: separate current radix tree from the one being built
  exec: put memory map in AddressSpaceDispatch
  exec: remove cur_map
  exec: change some APIs to take AddressSpaceDispatch
  exec: change iotlb APIs to take AddressSpaceDispatch
  exec: add a reference to the region returned by
    address_space_translate
  exec: put address space dispatch under RCU critical section

 aio-posix.c                 |   8 +
 aio-win32.c                 |  11 +-
 block/raw-posix.c           |   3 +
 block/raw-win32.c           |   3 +
 configure                   |  21 +++
 cpus.c                      |   3 +
 cputlb.c                    |   9 +-
 docs/atomics.txt            | 345 ++++++++++++++++++++++++++++++++++
 docs/rcu.txt                | 440 ++++++++++++++++++++++++++++++++++++++++++++
 exec.c                      | 244 ++++++++++++++++--------
 hw/9pfs/virtio-9p-synth.c   |   1 +
 hw/display/qxl.c            |   3 +-
 hw/ppc/spapr_iommu.c        |  10 +-
 hw/virtio/vhost.c           |   9 +-
 include/exec/cpu-all.h      |  14 +-
 include/exec/cputlb.h       |   9 +-
 include/exec/memory.h       |  77 ++++----
 include/qemu/atomic.h       | 190 +++++++++++++++----
 include/qemu/queue.h        |  13 ++
 include/qemu/rcu-pointer.h  | 110 +++++++++++
 include/qemu/rcu.h          | 180 ++++++++++++++++++
 include/qemu/thread-posix.h |   8 +
 include/qemu/thread-win32.h |   4 +
 include/qemu/thread.h       |  10 +-
 include/qemu/tls.h          | 125 +++++++++++--
 kvm-all.c                   |   3 +
 libcacard/Makefile          |   3 +-
 main-loop.c                 |   6 +
 memory.c                    | 127 +++++++++----
 migration.c                 |   5 +-
 tests/Makefile              |  10 +-
 tests/rcutorture.c          | 439 +++++++++++++++++++++++++++++++++++++++++++
 tests/test-thread-pool.c    |   8 +-
 tests/test-tls.c            |  87 +++++++++
 util/Makefile.objs          |   1 +
 util/qemu-thread-posix.c    | 174 +++++++++++++++++-
 util/qemu-thread-win32.c    |  61 +++++-
 util/rcu.c                  | 312 +++++++++++++++++++++++++++++++
 38 files changed, 2857 insertions(+), 229 deletions(-)
 create mode 100644 docs/atomics.txt
 create mode 100644 docs/rcu.txt
 create mode 100644 include/qemu/rcu-pointer.h
 create mode 100644 include/qemu/rcu.h
 create mode 100644 tests/rcutorture.c
 create mode 100644 tests/test-tls.c
 create mode 100644 util/rcu.c

-- 
1.8.1.4