On 2023/3/7 22:15, 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. > > 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! > Hi Ming, Maybe we can split patch 06-12 to a separate cleanup pacthset. I think these patches can be merged first because they are not related to zero copy. Regards, Zhang
