[Qemu-devel] [PATCH 00/13] linux-aio/virtio-scsi: support AioContext wide IO submission as batch

[Ming Lei <ming.lei@canonical.com>]

This patch implements AioContext wide IO submission as batch, and
the idea behind is very simple:

	- linux native aio(io_submit) supports to enqueue read/write requests
	to different files

	- in one AioContext, I/O requests from VM can be submitted to different
	backend in host, one typical example is multi-lun scsi 

This patch changes 'struct qemu_laio_state' as per AioContext, and
multiple 'bs' can be associted with one single instance of
'struct qemu_laio_state', then AioContext wide IO submission as batch
becomes easy to implement.

One simple test in my laptop shows ~20% throughput improvement
on randread from VM(using AioContext wide IO batch vs. not using io batch)
with below config:

	-drive id=drive_scsi1-0-0-0,if=none,format=raw,cache=none,aio=native,file=/dev/nullb2 \
	-drive id=drive_scsi1-0-0-1,if=none,format=raw,cache=none,aio=native,file=/dev/nullb3 \
	-device virtio-scsi-pci,num_queues=4,id=scsi1,addr=07,iothread=iothread0 \
	-device scsi-disk,bus=scsi1.0,channel=0,scsi-id=1,lun=0,drive=drive_scsi1-0-0-0,id=scsi1-0-0-0 \
	-device scsi-disk,bus=scsi1.0,channel=0,scsi-id=1,lun=1,drive=drive_scsi1-0-0-1,id=scsi1-0-0-1 \

BTW, maybe more boost can be obtained since ~33K/sec write() system call
can be observed when this test case is running, and it might be a recent
regression(BH?).

This patchset can be found on below tree too:

	git://kernel.ubuntu.com/ming/qemu.git aio-io-batch.2

and these patches depend on "linux-aio: fix batch submission" patches
in below link:

	http://marc.info/?l=qemu-devel&m=141528663106557&w=2

Any comments and suggestions are welcome.

 async.c                         |    1 +
 block.c                         |   16 +++
 block/linux-aio.c               |  251 ++++++++++++++++++++++++++++++---------
 block/raw-aio.h                 |    6 +-
 block/raw-posix.c               |    4 +-
 hw/scsi/virtio-scsi-dataplane.c |    8 ++
 hw/scsi/virtio-scsi.c           |    2 -
 include/block/aio.h             |   27 +++++
 include/block/block.h           |    3 +
 9 files changed, 259 insertions(+), 59 deletions(-)

Thanks,
Ming Lei