virtio-blk: add io_uring passthrough support for virtio-blk

We seek to develop a more flexible way to use virtio-blk and bypass the block
layer logic in order to accomplish certain performance optimizations. As a
result, we referred to the implementation of io_uring passthrough in NVMe
and implemented it in the virtio-blk driver. This patch series adds io_uring
passthrough support for virtio-blk devices, resulting in lower submit latency
and increased flexibility when utilizing virtio-blk.

To test this patch series, I changed fio's code: 
1. Added virtio-blk support to engines/io_uring.c.
2. Added virtio-blk support to the t/io_uring.c testing tool.
Link: https://github.com/jdmfr/fio 

Using t/io_uring-vblk, the performance of virtio-blk based on uring-cmd
scales better than block device access. (such as below, Virtio-Blk with QEMU,
1-depth fio) 
(passthru) read: IOPS=17.2k, BW=67.4MiB/s (70.6MB/s) 
slat (nsec): min=2907, max=43592, avg=3981.87, stdev=595.10 
clat (usec): min=38, max=285,avg=53.47, stdev= 8.28 
lat (usec): min=44, max=288, avg=57.45, stdev= 8.28
(block) read: IOPS=15.3k, BW=59.8MiB/s (62.7MB/s) 
slat (nsec): min=3408, max=35366, avg=5102.17, stdev=790.79 
clat (usec): min=35, max=343, avg=59.63, stdev=10.26 
lat (usec): min=43, max=349, avg=64.73, stdev=10.21

Testing the virtio-blk device with fio using 'engines=io_uring_cmd'
and 'engines=io_uring' also demonstrates improvements in submit latency.
(passthru) taskset -c 0 t/io_uring-vblk -b4096 -d8 -c4 -s4 -p0 -F1 -B0 -O0 -n1 -u1 /dev/vdcc0 
IOPS=189.80K, BW=741MiB/s, IOS/call=4/3
IOPS=187.68K, BW=733MiB/s, IOS/call=4/3 
(block) taskset -c 0 t/io_uring-vblk -b4096 -d8 -c4 -s4 -p0 -F1 -B0 -O0 -n1 -u0 /dev/vdc 
IOPS=101.51K, BW=396MiB/s, IOS/call=4/3
IOPS=100.01K, BW=390MiB/s, IOS/call=4/4

The performance overhead of submitting IO can be decreased by 25% overall
with this patch series. The implementation primarily references 'nvme io_uring
passthrough', supporting io_uring_cmd through a separate character interface
(temporarily named /dev/vdXc0). Since this is an early version, many
details need to be taken into account and redesigned, like:
● Currently, it only considers READ/WRITE scenarios, some more complex operations 
not included like discard or zone ops.(Normal sqe64 is sufficient, in my opinion;
following upgrades, sqe128 and cqe32 might not be needed).
● ......

I would appreciate any useful recommendations.

Ferry Meng (3):
  virtio-blk: add virtio-blk chardev support.
  virtio-blk: add uring_cmd support for I/O passthru on chardev.
  virtio-blk: add uring_cmd iopoll support.

 drivers/block/virtio_blk.c      | 325 +++++++++++++++++++++++++++++++-
 include/uapi/linux/virtio_blk.h |  16 ++
 2 files changed, 336 insertions(+), 5 deletions(-)

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2.43.5