[v1,0/3] virtio-blk: add io_uring passthrough support.

Message

Ferry Meng Dec. 18, 2024, 9:24 a.m. UTC

This patchset implements io_uring passthrough surppot in virtio-blk
driver, bypass vfs and part of block layer logic, resulting in lower
submit latency and increased flexibility when utilizing virtio-blk.

In this version, currently only supports READ/WRITE vec/no-vec operations,
others like discard or zoned ops not considered in. So the userspace-related
struct is not complicated.

struct virtblk_uring_cmd {
	__u32 type;
	__u32 ioprio;
	__u64 sector;
	/* above is related to out_hdr */
	__u64 data;  // user buffer addr or iovec base addr.
	__u32 data_len; // user buffer length or iovec count.
	__u32 flag;  // only contains whether a vector rw or not.
}; 

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


===========
Performance
===========

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

=======
Changes
=======

Changes in v1:
--------------
* remove virtblk_is_write() helper
* fix rq_flags type definition (blk_opf_t), add REQ_ALLOC_CACHE flag.
https://lore.kernel.org/io-uring/[e-mail]/

RFC discussion:
---------------
https://lore.kernel.org/io-uring/[e-mail]/

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      | 320 +++++++++++++++++++++++++++++++-
 include/uapi/linux/virtio_blk.h |  16 ++
 2 files changed, 331 insertions(+), 5 deletions(-)