Re: [PATCH V6 00/17] io_uring/ublk: add generic IORING_OP_FUSED_CMD

[Ming Lei]

On Thu, Mar 30, 2023 at 07:36:13PM +0800, Ming Lei wrote:
> Hello Jens and Guys,
> 
> Add generic fused command, which can include one primary command and multiple
> secondary requests. This command provides one safe way to share resource between
> primary command and secondary requests, and primary command is always
> completed after all secondary requests are done, and resource lifetime
> is bound with primary command.
> 
> With this way, it is easy to support zero copy for ublk/fuse device, and
> there could be more potential use cases, such as offloading complicated logic
> into userspace, or decouple kernel subsystems.
> 
> Follows ublksrv code, which implements zero copy for loop, nbd and
> qcow2 targets with fused command:
> 
> https://github.com/ming1/ubdsrv/tree/fused-cmd-zc-for-v6
> 
> All three(loop, nbd and qcow2) ublk targets have supported zero copy by passing:
> 
> 	ublk add -t [loop|nbd|qcow2] -z .... 
> 
> Also add liburing test case for covering fused command based on miniublk
> of blktest.
> 
> https://github.com/ming1/liburing/tree/fused_cmd_miniublk_for_v6
> 
> 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.
> ublk-null shows 5X IOPS improvement on big BS test when the copy is avoided.
> 
> Please review and consider for v6.4.
> 
> V6:
> 	- re-design fused command, and make it more generic, moving sharing buffer
> 	as one plugin of fused command, so in future we can implement more plugins
> 	- document potential other use cases of fused command
> 	- drop support for builtin secondary sqe in SQE128, so all secondary
> 	  requests has standalone SQE
> 	- make fused command as one feature
> 	- cleanup & improve naming

Hi Jens,

Can you apply ublk cleanup patches 7~11 on for-6.4? For others, we may
delay to 6.5, and I am looking at other approach too.


Thanks,
Ming