[dm-devel] [RFC PATCH V2 00/13] block: support bio based io polling

[JeffleXu]

On 3/19/21 12:48 AM, Ming Lei wrote:
> Hi,
> 
> 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.
> 
> Any comments are welcome.
> 
> 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.

I have retested this latest version, and it seems the scaling issue has
been fixed at the first glance.

Test results with the latest version:
3-threads  dm-stripe-3 targets  (12k randread IOPS, unit K)
317 -> 409 (iodepth=128)

Compared to the test results of v1:
3-threads  dm-stripe-3 targets  (12k randread IOPS, unit K)
313 -> 349 (iodepth=128, kfifo queue depth =128)
313 -> 409 (iodepth=32, kfifo queue depth =128)
314 -> 409 (iodepth=128, kfifo queue depth =512)

> 
> 
> Jeffle Xu (4):
>   block/mq: extract one helper function polling hw queue
>   block: add queue_to_disk() to get gendisk from request_queue
>   block: add poll_capable method to support bio-based IO polling
>   dm: support IO polling for bio-based dm device
> 
> Ming Lei (9):
>   block: add helper of blk_queue_poll
>   block: add one helper to free io_context
>   block: add helper of blk_create_io_context
>   block: create io poll context for submission and poll task
>   block: add req flag of REQ_TAG
>   block: add new field into 'struct bvec_iter'
>   block: prepare for supporting bio_list via other link
>   block: use per-task poll context to implement bio based io poll
>   blk-mq: limit hw queues to be polled in each blk_poll()
> 
>  block/bio.c                   |   5 +
>  block/blk-core.c              | 248 ++++++++++++++++++++++++++++++++--
>  block/blk-ioc.c               |  12 +-
>  block/blk-mq.c                | 232 ++++++++++++++++++++++++++++++-
>  block/blk-sysfs.c             |  14 +-
>  block/blk.h                   |  55 ++++++++
>  drivers/md/dm-table.c         |  24 ++++
>  drivers/md/dm.c               |  14 ++
>  drivers/nvme/host/core.c      |   2 +-
>  include/linux/bio.h           | 132 +++++++++---------
>  include/linux/blk_types.h     |  20 ++-
>  include/linux/blkdev.h        |   4 +
>  include/linux/bvec.h          |   9 ++
>  include/linux/device-mapper.h |   1 +
>  include/linux/iocontext.h     |   2 +
>  include/trace/events/kyber.h  |   6 +-
>  16 files changed, 686 insertions(+), 94 deletions(-)
> 

-- 
Thanks,
Jeffle