Re: [PATCH V6 00/12] block: support bio based io polling

[JeffleXu <jefflexu@linux.alibaba.com>]

Hi all,

What's the latest progress of this bio-based polling feature?

I've noticed that hch has also sent a patch set on this [1]. But as far
as I know, hch's patch set only refactors the interface of polling in
the block layer. It indeed helps bio-based polling for some kind of
bio-based driver, but for DM/MD where one bio could be mapped to several
split bios, more work is obviously needed, just like Lei Ming's
io_context related code in this patch set.

hch may have better idea, after all [1] is just a preparation patch set.


[1]
https://lore.kernel.org/linux-block/20210427161619.1294399-2-hch@lst.de/T/


-- 
Thanks,
Jeffle


On 4/22/21 8:20 PM, Ming Lei wrote:
> Hi Jens,
> 
> Add per-task io poll context for holding HIPRI blk-mq/underlying bios
> queued from bio based driver's io submission context, and reuse one bio
> padding field for storing 'cookie' returned from submit_bio() for these
> bios. Also explicitly end these bios in poll context by adding two
> new bio flags.
> 
> In this way, we needn't to poll all underlying hw queues any more,
> which is implemented in Jeffle's patches. And we can just poll hw queues
> in which there is HIPRI IO queued.
> 
> Usually io submission and io poll share same context, so the added io
> poll context data is just like one stack variable, and the cost for
> saving bios is cheap.
> 
> V6:
> 	- move poll code into block/blk-poll.c, as suggested by Christoph
> 	- define bvec_iter as __packed, and add one new field to bio, as
> 	  suggested by Christoph
> 	- re-organize patch order, as suggested by Christoph
> 	- add one flag for checking if the disk is capable of bio polling
> 	  and remove .poll_capable(), as suggested by Christoph
> 	- fix type of .bi_poll
> 
> V5:
> 	- fix one use-after-free issue in case that polling is from another
> 	context: adds one new cookie of BLK_QC_T_NOT_READY for preventing
> 	this issue in patch 8/12
> 	- add reviewed-by & tested-by tag
> 
> V4:
> 	- cover one more test_bit(QUEUE_FLAG_POLL, ...) suggested by
> 	  Jeffle(01/12)
> 	- drop patch of 'block: add helper of blk_create_io_context'
> 	- add new helper of blk_create_io_poll_context() (03/12)
> 	- drain submission queues in exit_io_context(), suggested by
> 	  Jeffle(08/13)
> 	- considering shared io context case for blk_bio_poll_io_drain()
> 	(08/13)
> 	- fix one issue in blk_bio_poll_pack_groups() as suggested by
> 	Jeffle(08/13)
> 	- add reviewed-by tag
> V3:
> 	- fix cookie returned for bio based driver, as suggested by Jeffle Xu
> 	- draining pending bios when submission context is exiting
> 	- patch style and comment fix, as suggested by Mike
> 	- allow poll context data to be NULL by always polling on submission queue
> 	- remove RFC, and reviewed-by
> 
> V2:
> 	- address queue depth scalability issue reported by Jeffle via bio
> 	group list. Reuse .bi_end_io for linking bios which share same
> 	.bi_end_io, and support 32 such groups in submit queue. With this way,
> 	the scalability issue caused by kfifio is solved. Before really
> 	ending bio, .bi_end_io is recovered from the group head.
> 
> 
> 
> Jeffle Xu (2):
>   block: extract one helper function polling hw queue
>   dm: support IO polling for bio-based dm device
> 
> Ming Lei (10):
>   block: add helper of blk_queue_poll
>   block: define 'struct bvec_iter' as packed
>   block: add one helper to free io_context
>   block: move block polling code into one dedicated source file
>   block: prepare for supporting bio_list via other link
>   block: create io poll context for submission and poll task
>   block: add req flag of REQ_POLL_CTX
>   block: use per-task poll context to implement bio based io polling
>   block: limit hw queues to be polled in each blk_poll()
>   block: allow to control FLAG_POLL via sysfs for bio poll capable queue
> 
>  block/Makefile                |   3 +-
>  block/bio.c                   |   5 +
>  block/blk-core.c              |  68 +++-
>  block/blk-ioc.c               |  15 +-
>  block/blk-mq.c                | 231 -------------
>  block/blk-mq.h                |  40 +++
>  block/blk-poll.c              | 632 ++++++++++++++++++++++++++++++++++
>  block/blk-sysfs.c             |  16 +-
>  block/blk.h                   | 112 ++++++
>  drivers/md/dm-table.c         |  24 ++
>  drivers/md/dm.c               |   2 +
>  drivers/nvme/host/core.c      |   2 +-
>  include/linux/bio.h           | 132 +++----
>  include/linux/blk_types.h     |  31 +-
>  include/linux/blkdev.h        |   1 +
>  include/linux/bvec.h          |   2 +-
>  include/linux/device-mapper.h |   1 +
>  include/linux/genhd.h         |   2 +
>  include/linux/iocontext.h     |   2 +
>  19 files changed, 1003 insertions(+), 318 deletions(-)
>  create mode 100644 block/blk-poll.c
>