On Wed, Jan 18, 2017 at 05:31:03PM +0100, Paolo Bonzini wrote: > > > On 18/01/2017 17:03, Stefan Hajnoczi wrote: > > On Fri, Jan 13, 2017 at 02:17:15PM +0100, Paolo Bonzini wrote: > >> This series pushes down aio_context_acquire/release to the point > >> where we can actually reason on using different fine-grained mutexes. > >> > >> The main infrastructure is introduced in patch 1. The new API aio_co_wake > >> starts a coroutine with aio_context_acquire/release protection, which > >> requires tracking each coroutine's "home" AioContext. aio_co_schedule > >> instead takes care of moving a sleeping coroutine to a different > >> AioContext, also ensuring that it runs under aio_context_acquire/release. > >> This is useful to implement bdrv_set_aio_context, as a simpler alternative > >> to bottom halves. Even though one-shot BHs are already simpler than > >> what we had before, after this patch aio_co_wake and aio_co_schedule > >> save you from having to do aio_context_acquire/release explicitly. > >> > >> After patch 2 and 3, which are just small preparatory changes, patches > >> 4 to 7 provide an example of how to use the new API. In particular patch > >> 4 to 6 implement a new organization of coroutines in the NBD client, > >> which allows not blocking on partial reply header reads. > >> > >> Patch 8 introduces helpers for AioContext locking in QED, which is > >> the most complex AIO-based driver left. Then the actual meat of the > >> series runs from patch 9 to patch 13, followed by small optimizations > >> in patches 14 and 15. > >> > >> The patches do some back and forth in adding/removing > >> aio_context_acquire/release calls in block/*.c but ultimately a small > >> number of aio_context_acquire/release pairs are added after the pushdown. > >> These are mostly in drivers that use external libraries (where they > >> actually could already be replaced by QemuMutex) and in device models. > >> > >> Notably, coroutines need not care about aio_context_acquire/release. > >> The device models ensure that the first creation of the coroutine has > >> the AioContext, while aio_co_wake/aio_co_schedule do the same after > >> they yield. Therefore, most of the files only need to use those two > >> functions instead of, respectively, qemu_coroutine_enter and > >> aio_bh_schedule_oneshot. > >> > >> However, this is only an intermediate step which is needed because the > >> block layer and qemu-coroutine locks are thread-unsafe. So the next > >> part will add separate locking, independent of AioContext, to block.c and > >> mostly block/io.c---this includes making CoMutex thread-safe. Patch 16 > >> therefore already documents the current locking policies block.h to > >> prepare for the next series. > >> > >> Paolo > >> > >> Paolo Bonzini (16): > >> aio: introduce aio_co_schedule and aio_co_wake > >> block-backend: allow blk_prw from coroutine context > >> test-thread-pool: use generic AioContext infrastructure > >> io: add methods to set I/O handlers on AioContext > >> io: make qio_channel_yield aware of AioContexts > >> nbd: do not block on partial reply header reads > >> coroutine-lock: reschedule coroutine on the AioContext it was running > >> on > >> qed: introduce qed_aio_start_io and qed_aio_next_io_cb > >> aio: push aio_context_acquire/release down to dispatching > >> block: explicitly acquire aiocontext in timers that need it > >> block: explicitly acquire aiocontext in callbacks that need it > >> block: explicitly acquire aiocontext in bottom halves that need it > >> block: explicitly acquire aiocontext in aio callbacks that need it > >> aio-posix: partially inline aio_dispatch into aio_poll > >> async: remove unnecessary inc/dec pairs > >> block: document fields protected by AioContext lock > >> > >> aio-posix.c | 60 +++--------- > >> aio-win32.c | 30 ++---- > >> async.c | 81 ++++++++++++++-- > >> block/blkdebug.c | 9 +- > >> block/blkreplay.c | 2 +- > >> block/block-backend.c | 13 ++- > >> block/curl.c | 44 ++++++--- > >> block/gluster.c | 9 +- > >> block/io.c | 4 +- > >> block/iscsi.c | 15 ++- > >> block/linux-aio.c | 10 +- > >> block/mirror.c | 12 ++- > >> block/nbd-client.c | 108 ++++++++------------- > >> block/nbd-client.h | 2 +- > >> block/nfs.c | 9 +- > >> block/qed-cluster.c | 2 + > >> block/qed-table.c | 12 ++- > >> block/qed.c | 58 +++++++---- > >> block/qed.h | 3 + > >> block/sheepdog.c | 29 +++--- > >> block/ssh.c | 29 ++---- > >> block/throttle-groups.c | 2 + > >> block/win32-aio.c | 9 +- > >> dma-helpers.c | 2 + > >> hw/block/virtio-blk.c | 19 +++- > >> hw/scsi/scsi-bus.c | 2 + > >> hw/scsi/scsi-disk.c | 15 +++ > >> hw/scsi/scsi-generic.c | 20 +++- > >> hw/scsi/virtio-scsi.c | 6 ++ > >> include/block/aio.h | 38 +++++++- > >> include/block/block_int.h | 64 ++++++++----- > >> include/io/channel.h | 59 +++++++++++- > >> include/qemu/coroutine_int.h | 10 +- > >> include/sysemu/block-backend.h | 14 ++- > >> io/channel-command.c | 13 +++ > >> io/channel-file.c | 11 +++ > >> io/channel-socket.c | 16 +++- > >> io/channel-tls.c | 12 +++ > >> io/channel-watch.c | 6 ++ > >> io/channel.c | 97 +++++++++++++++---- > >> nbd/client.c | 2 +- > >> nbd/common.c | 9 +- > >> nbd/server.c | 4 + > >> tests/Makefile.include | 15 ++- > >> tests/iothread.c | 91 ++++++++++++++++++ > >> tests/iothread.h | 25 +++++ > >> tests/test-aio-multithread.c | 213 +++++++++++++++++++++++++++++++++++++++++ > >> tests/test-thread-pool.c | 12 +-- > >> tests/test-vmstate.c | 11 --- > >> thread-pool.c | 6 +- > >> trace-events | 4 + > >> util/qemu-coroutine-lock.c | 5 +- > >> util/qemu-coroutine-sleep.c | 2 +- > >> util/qemu-coroutine.c | 8 ++ > >> util/trace-events | 1 - > >> 55 files changed, 1012 insertions(+), 352 deletions(-) > >> create mode 100644 tests/iothread.c > >> create mode 100644 tests/iothread.h > >> create mode 100644 tests/test-aio-multithread.c > > > > This is a big and somewhat risky change. Have you run any performance > > benchmarks? > > Not recently; I ran them a year ago and there was no measurable difference. Good, please re-run for the final version.