Re: [PATCH 0/3][RFC] virtio-blk: add io_uring passthrough support for virtio-blk

[Jason Wang <jasowang@redhat.com>]

On Mon, Dec 16, 2024 at 10:01 AM Ferry Meng <mengferry@linux.alibaba.com> wrote:
>
>
> On 12/3/24 8:14 PM, Ferry Meng wrote:
> > 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(-)
>
> Hi, Micheal & Jason :
>
> What about yours' opinion? As virtio-blk maintainer. Looking forward to
> your reply.
>
> Thanks

If I understand this correctly, this proposal wants to make io_uring a
transport of the virito-blk command. So the application doesn't need
to worry about compatibility etc. This seems to be fine.

But I wonder what's the security consideration, for example do we
allow all virtio-blk commands to be passthroughs and why.

Thanks

>