[RFC 0/2] optimise local-tw task resheduling

Pavel Begunkov
2023-03-10T19:05:39Z

io_uring extensively uses task_work, but when a task is waiting
for multiple CQEs it causes lots of rescheduling. This series
is an attempt to optimise it and be a base for future improvements.

For some zc network tests eventually waiting for a portion of
buffers I've got 10x descrease in the number of context switches,
which reduced the CPU consumption more than twice (17% -> 8%).
It also helps storage cases, while running fio/t/io_uring against
a low performant drive it got 2x descrease of the number of context
switches for QD8 and ~4 times for QD32.

Not for inclusion yet, I want to add an optimisation for when
waiting for 1 CQE.

Pavel Begunkov (2):
io_uring: add tw add flags
io_uring: reduce sheduling due to tw

include/linux/io_uring_types.h | 2 +-
io_uring/io_uring.c | 48 ++++++++++++++++++++--------------
io_uring/io_uring.h | 10 +++++--
io_uring/notif.h | 2 +-
io_uring/rw.c | 2 +-
5 files changed, 40 insertions(+), 24 deletions(-)

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2.39.1