On 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? If 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. > > 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 > >
