On Wed, Jul 29, 2015 at 12:42:03PM +0800, Fam Zheng wrote:
> v2: Switch to disable/enable model. [Paolo]
>
> Most existing nested aio_poll()'s in block layer are inconsiderate of
> dispatching potential new r/w requests from ioeventfds and nbd exports, which
> might result in responsiveness issues (e.g. bdrv_drain_all will not return
> when
> new requests keep coming), or even wrong semantics (e.g. qmp_transaction
> cannot
> enforce atomicity due to aio_poll in bdrv_drain_all).
>
> Previous attampts to address this issue include new op blocker[1],
> bdrv_lock[2]
> and nested AioContext (patches not posted to qemu-devel).
>
> This approach is based on the idea proposed by Paolo Bonzini. The original
> idea
> is introducing "aio_context_disable_client / aio_context_enable_client to
> filter AioContext handlers according to the "client", e.g.
> AIO_CLIENT_DATAPLANE (ioeventfd), AIO_CLIENT_PROTOCOL, AIO_CLIENT_NBD_SERVER,
> AIO_CLIENT_CONTEXT, ... Extend aio_set_{event_notifier,fd}_handler to pass a
> client (type)."
>
> After this series, block layer aio_poll() will only process those "protocol"
> fds that are used in block I/O, plus the ctx->notifier for aio_notify();
> other
> aio_poll()'s keep unchanged.
>
> The biggest advantage over approaches [1] and [2] is, no change is needed in
> virtio-{blk,scsi}-dataplane code, also this doesn't depend on converting QMP
> to
> coroutines.
>
> The windows implementation is not tested except for compiling.
>
> [1]: https://lists.gnu.org/archive/html/qemu-block/2015-05/msg00800.html
> [2]: http://lists.nongnu.org/archive/html/qemu-block/2015-06/msg00027.html
>
>
> Fam Zheng (11):
> aio: Introduce "type" in aio_set_fd_handler and aio_set_event_notifier
> aio: Save type to AioHandler
> block: Mark fd handlers as "protocol"
> nbd: Mark fd handlers client type as "nbd server"
> aio: Mark ctx->notifier's client type as "context"
> dataplane: Mark host notifiers' client type as "dataplane"
> aio-posix: introduce aio_{disable,enable}_clients
> aio-win32: Implement aio_{disable,enable}_clients
> block: Introduce bdrv_aio_poll
> block: Replace nested aio_poll with bdrv_aio_poll
> block: Only poll block layer fds in bdrv_aio_poll
>
> aio-posix.c | 23 ++++++++++++++--
> aio-win32.c | 22 +++++++++++++++-
> async.c | 3 ++-
> block.c | 2 +-
> block/curl.c | 16 +++++++-----
> block/io.c | 28 +++++++++++++-------
> block/iscsi.c | 9 +++----
> block/linux-aio.c | 5 ++--
> block/nbd-client.c | 10 ++++---
> block/nfs.c | 19 ++++++--------
> block/qed-table.c | 8 +++---
> block/sheepdog.c | 32 +++++++++++++++--------
> block/ssh.c | 5 ++--
> block/win32-aio.c | 5 ++--
> blockjob.c | 2 +-
> hw/block/dataplane/virtio-blk.c | 6 +++--
> hw/scsi/virtio-scsi-dataplane.c | 24 +++++++++++------
> include/block/aio.h | 33 +++++++++++++++++++++++
> include/block/block.h | 2 ++
> nbd.c | 4 ++-
> qemu-img.c | 2 +-
> qemu-io-cmds.c | 4 +--
> tests/test-aio.c | 58
> +++++++++++++++++++++++------------------
> 23 files changed, 219 insertions(+), 103 deletions(-)
What is the status of this series?
Paolo's points about Patch 11 & 12 stand. It seems the fd type concept
is good but the bdrv_aio_poll() mechanism requires changes to fully
solve the problem.
Stefan
