Re: [RFC PATCH V2 0/9] io_uring: support sqe group and provide group kbuf

[Ming Lei <ming.lei@redhat.com>]

On Tue, May 07, 2024 at 12:22:36AM +0800, Ming Lei wrote:
> Hello,
> 
> The 1st 4 patches are cleanup, and prepare for adding sqe group.
> 
> The 5th patch supports generic sqe group which is like link chain, but
> allows each sqe in group to be issued in parallel, so N:M dependency can be
> supported with sqe group & io link together.
> 
> The 6th patch supports one variant of sqe group: allow members to depend
> on group leader, so that kernel resource lifetime can be aligned with
> group leader or group, then any kernel resource can be shared in this
> sqe group, and can be used in generic device zero copy.
> 
> The 7th & 8th patches supports providing sqe group buffer via the sqe
> group variant.
> 
> The 9th patch supports ublk zero copy based on io_uring providing sqe
> group buffer.
> 
> Tests:
> 
> 1) pass liburing test
> - make runtests
> 
> 2) write/pass two sqe group test cases:
> 
> https://github.com/axboe/liburing/compare/master...ming1:liburing:sqe_group_v2
> 
> covers related sqe flags combination and linking groups, both nop and
> one multi-destination file copy.
> 
> 3) ublksrv zero copy:
> 
> ublksrv userspace implements zero copy by sqe group & provide group
> kbuf:
> 
> 	git clone https://github.com/ublk-org/ublksrv.git -b group-provide-buf_v2
> 	make test T=loop/009:nbd/061:nbd/062	#ublk zc tests
> 
> When running 64KB block size test on ublk-loop('ublk add -t loop --buffered_io -f $backing'),
> it is observed that perf can be doubled.
> 
> Any comments are welcome!
> 
> V2:
> 	- add generic sqe group, suggested by Kevin Wolf
> 	- add REQ_F_SQE_GROUP_DEP which is based on IOSQE_SQE_GROUP, for sharing
> 	  kernel resource in group wide, suggested by Kevin Wolf
> 	- remove sqe ext flag, and use the last bit for IOSQE_SQE_GROUP(Pavel),
> 	in future we still can extend sqe flags with one uring context flag
> 	- initialize group requests via submit state pattern, suggested by Pavel
> 	- all kinds of cleanup & bug fixes

Please ignore V2, and will send V3 with simplification & cleanup, and
many fixes on error handling code path.


Thanks,
Ming