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

Message

Ming Lei April 22, 2021, 12:20 p.m. UTC

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

Comments

Jingbo Xu May 17, 2021, 6:16 a.m. UTC | #1

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/[e-mail]/T/

Ming Lei May 17, 2021, 7:13 a.m. UTC | #2

Hi JeffleXu,

On Mon, May 17, 2021 at 02:16:39PM +0800, JeffleXu wrote:
> 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.

Yeah, we have to rebase V6 against Christoph's patchset anyway.

Looks there is at least two approaches left for us:

1) keep the generic approach in V6, just rebase after Christoph's patch
is finalized

2) support io polling simply in bio driver, since bio->bi_cookie is
assigned for underlying bio, and it shouldn't be very difficult to
support that in DM/MD. I have been thinking of it a while, but not
coding it yet. BTW, all underlying bios can be linked to DM
bio->bi_next, and we can add one new callback of .io_poll for polling
DM/MD's bio.


Thanks,
Ming