On 3/7/23 14:15, Ming Lei wrote:
Hello, Add IORING_OP_FUSED_CMD, it is one special URING_CMD, which has to be SQE128. The 1st SQE(master) is one 64byte URING_CMD, and the 2nd 64byte SQE(slave) is another normal 64byte OP. For any OP which needs to support slave OP, io_issue_defs[op].fused_slave needs to be set as 1, and its ->issue() can retrieve/import buffer from master request's fused_cmd_kbuf. The slave OP is actually submitted from kernel, part of this idea is from Xiaoguang's ublk ebpf patchset, but this patchset submits slave OP just like normal OP issued from userspace, that said, SQE order is kept, and batching handling is done too.
From a quick look through patches it all looks a bit complicated and intrusive, all over generic hot paths. I think instead we should be able to use registered buffer table as intermediary and reuse splicing. Let me try it out
Please see detailed design in commit log of the 3th patch, and one big point is how to handle buffer ownership. With this way, it is easy to support zero copy for ublk/fuse device. Basically userspace can specify any sub-buffer of the ublk block request buffer from the fused command just by setting 'offset/len' in the slave SQE for running slave OP. This way is flexible to implement io mapping: mirror, stripped, ... The 4th & 5th patches enable fused slave support for the following OPs: OP_READ/OP_WRITE OP_SEND/OP_RECV/OP_SEND_ZC The other ublk patches cleans ublk driver and implement fused command for supporting zero copy. Follows userspace code: https://github.com/ming1/ubdsrv/tree/fused-cmd-zc-v2 All three(loop, nbd and qcow2) ublk targets have supported zero copy by passing: ublk add -t [loop|nbd|qcow2] -z .... Basic fs mount/kernel building and builtin test are done. Also add liburing test case for covering fused command based on miniublk of blktest: https://github.com/ming1/liburing/commits/fused_cmd_miniublk Performance improvement is obvious on memory bandwidth related workloads, such as, 1~2X improvement on 64K/512K BS IO test on loop with ramfs backing file. Any comments are welcome! V2: - don't resue io_mapped_ubuf (io_uring) - remove REQ_F_FUSED_MASTER_BIT (io_uring) - fix compile warning (io_uring) - rebase on v6.3-rc1 (io_uring) - grabbing io request reference when handling fused command - simplify ublk_copy_user_pages() by iov iterator - add read()/write() for userspace to read/write ublk io buffer, so that some corner cases(read zero, passthrough request(report zones)) can be handled easily in case of zero copy; this way also helps to switch to zero copy completely - misc cleanup Ming Lei (17): io_uring: add IO_URING_F_FUSED and prepare for supporting OP_FUSED_CMD io_uring: increase io_kiocb->flags into 64bit io_uring: add IORING_OP_FUSED_CMD io_uring: support OP_READ/OP_WRITE for fused slave request io_uring: support OP_SEND_ZC/OP_RECV for fused slave request block: ublk_drv: mark device as LIVE before adding disk block: ublk_drv: add common exit handling block: ublk_drv: don't consider flush request in map/unmap io block: ublk_drv: add two helpers to clean up map/unmap request block: ublk_drv: clean up several helpers block: ublk_drv: cleanup 'struct ublk_map_data' block: ublk_drv: cleanup ublk_copy_user_pages block: ublk_drv: grab request reference when the request is handled by userspace block: ublk_drv: support to copy any part of request pages block: ublk_drv: add read()/write() support for ublk char device block: ublk_drv: don't check buffer in case of zero copy block: ublk_drv: apply io_uring FUSED_CMD for supporting zero copy drivers/block/ublk_drv.c | 605 ++++++++++++++++++++++++++------- drivers/char/mem.c | 4 + drivers/nvme/host/ioctl.c | 9 + include/linux/io_uring.h | 49 ++- include/linux/io_uring_types.h | 18 +- include/uapi/linux/io_uring.h | 1 + include/uapi/linux/ublk_cmd.h | 37 +- io_uring/Makefile | 2 +- io_uring/fused_cmd.c | 232 +++++++++++++ io_uring/fused_cmd.h | 11 + io_uring/io_uring.c | 22 +- io_uring/io_uring.h | 3 + io_uring/net.c | 23 +- io_uring/opdef.c | 17 + io_uring/opdef.h | 2 + io_uring/rw.c | 20 ++ 16 files changed, 926 insertions(+), 129 deletions(-) create mode 100644 io_uring/fused_cmd.c create mode 100644 io_uring/fused_cmd.h
-- Pavel Begunkov