Re: [PATCH V2 00/17] io_uring/ublk: add IORING_OP_FUSED_CMD

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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



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