[PATCH 0/2] improve SQPOLL handling

[Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>]

The first patch tries to improve various issues in current implementation:
  The prepare_to_wait() usage in __io_sq_thread() is weird. If multiple ctxs
share one same poll thread, one ctx will put poll thread in TASK_INTERRUPTIBLE,
but if other ctxs have work to do, we don't need to change task's stat at all.
I think only if all ctxs don't have work to do, we can do it.
  We use round-robin strategy to make multiple ctxs share one same poll thread,
but there are various condition in __io_sq_thread(), which seems complicated and
may affect round-robin strategy.
  In io_sq_thread(), we always call io_sq_thread_drop_mm() when we complete a
round of ctxs iteration, which maybe inefficient.

The second patch adds a IORING_SETUP_SQPOLL_PERCPU flag, for those rings which
have SQPOLL enabled and are willing to be bound to one same cpu, hence share
one same poll thread, add a capability that these rings can share one poll thread
by specifying a new IORING_SETUP_SQPOLL_PERCPU flag. FIO tool can integrate this
feature easily, so we can test multiple rings to share same poll thread easily.

Xiaoguang Wang (2):
  io_uring: refactor io_sq_thread() handling
  io_uring: support multiple rings to share same poll thread by
    specifying same cpu

 fs/io_uring.c                 | 307 ++++++++++++++++++++--------------
 include/uapi/linux/io_uring.h |   1 +
 2 files changed, 181 insertions(+), 127 deletions(-)

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2.17.2