[RFC PATCH 0/2] io_uring: fix io may accumulation in poll mode

[Fengnan Chang <fengnanchang@gmail.com>]

In the io_do_iopoll function, when the poll loop of iopoll_list ends, it
is considered that the current req is the actual completed request.
This may be reasonable for multi-queue ctx, but is problematic for
single-queue ctx because the current request may not be done when the
poll gets to the result. In this case, the completed io needs to wait
for the first io on the chain to complete before notifying the user,
which may cause io accumulation in the list.
Our modification plan is as follows: change io_wq_work_list to normal
list so that the iopoll_list list in it can be removed and put into the
comp_reqs list when the request is completed. This way each io is
handled independently and all gets processed in time.

After modification,  test with:

./t/io_uring -p1 -d128 -b4096 -s32 -c32 -F1 -B1 -R1 -X1 -n1 -P1
/dev/nvme6n1

base IOPS is 725K,  patch IOPS is 782K.

./t/io_uring -p1 -d128 -b4096 -s32 -c1 -F1 -B1 -R1 -X1 -n1 -P1
/dev/nvme6n1

Base IOPS is 880k, patch IOPS is 895K.

Fengnan Chang (2):
  blk-mq: delete task running check in blk_hctx_poll
  io_uring: fix io may accumulation in poll mode

 block/blk-mq.c                 |  2 --
 include/linux/blk-mq.h         |  1 +
 include/linux/blkdev.h         |  1 +
 include/linux/io_uring_types.h |  8 +++---
 io_uring/io_uring.c            | 51 ++++++++++++++++------------------
 io_uring/io_uring.h            | 15 ++++------
 io_uring/rw.c                  | 35 +++++++----------------
 io_uring/slist.h               |  9 ------
 io_uring/sqpoll.c              |  8 +++---
 9 files changed, 49 insertions(+), 81 deletions(-)


base-commit: 4941a17751c99e17422be743c02c923ad706f888
prerequisite-patch-id: 14d5e19968d0acb074ebcd62f073c330b0e34f36
prerequisite-patch-id: 1b5c18a564a4b4788f4992dc02d70c01f69c0e0e
-- 
2.39.5 (Apple Git-154)