Resend after change this into plain text. On 12/5/24 5:47 AM, Stefan Hajnoczi wrote:
Sure, this series only works with guest os, not between host and guest. Well, 'io_uring passthrough' gives a 'fast path for I/O' , and is ideal for our use case --- like using virtio-blk with command directlyOn Tue, 3 Dec 2024 at 07:17, Ferry Meng <mengferry@xxxxxxxxxxxxxxxxx> 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.First I thought this was similar to Stefano Garzarella's previous virtio-blk io_uring passthrough work where a host io_uring was passed through into the guest: https://static.sched.com/hosted_files/kvmforum2020/9c/KVMForum_2020_io_uring_passthrough_Stefano_Garzarella.pdf But now I see this is a uring_cmd interface for sending virtio_blk commands from userspace like the one offered by the NVMe driver. Unlike NVMe, the virtio-blk command set is minimal and does not offer a rich set of features. Is the motivation really virtio-blk command passthrough or is the goal just to create a fast path for I/O?
from userspace scales better.
If I understand correctly, io_uring passthrough is already a complete abstract framework for I/O request dispatch. Its aim is to allow driver to handle commands on its own with bypass unused logic. Thus I chose this method of implementation. I really agreed that the command set of virtio-blk is sufficient and minimal enough, but I also believe that this makes it more convenient for us to adapt all command types with fewer modifications, so that virtio-blkIf the goal is just a fast path for I/O, then maybe Jens would consider a generic command set that is not device-specific? That way any driver (NVMe, virtio-blk, etc) can implement this uring_cmd interface and any application can use it without worrying about the underlying command set. I think a generic fast path would be much more useful to applications than driver-specific interfaces.
can use io_uring passthrough. Of course, we can wait for Jens' view on the preceding discussion.
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(-) -- 2.43.5
