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

JeffleXu
2021-05-17T06:16:44Z

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
>