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

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Message-Id: <cover.1678474375.git.asml.silence@gmail.com>
Date:   Fri, 10 Mar 2023 19:04:14 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     io-uring@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>, asml.silence@...il.com,
        linux-kernel@...r.kernel.org
Subject: [RFC 0/2] optimise local-tw task resheduling

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(-)

-- 
2.39.1