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

[Paolo Bonzini <pbonzini@redhat.com>]

On 09/11/2014 08:42, Ming Lei wrote:
> 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?).

Ming,

these patches are interesting.  I would like to compare them with the
opposite approach (and, I think, more similar to your old work) where
the qemu_laio_state API is moved entirely into AioContext, with lazy
allocation (reference-counted too, probably).

Most of the patches would be the same, but you would replace
aio_attach_aio_bs/aio_detach_aio_bs with something like
aio_native_get/aio_native_unref.  Ultimately block/{linux,win32}-aio.c
could be merged into block/aio-{posix,win32}.c, but you do not have to
do that now.

Could you try that?  This way we can see which API turns out to be nicer.

Thanks,

Paolo

> 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
>