linux-kernel - [PATCH 0/2] optimise blk_try_enter

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Message-Id: <cover.1634759754.git.asml.silence@gmail.com>
Date:   Wed, 20 Oct 2021 21:03:17 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     linux-block@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Christoph Lameter <cl@...ux.com>,
        Tejun Heo <tj@...nel.org>, Dennis Zhou <dennis@...nel.org>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [PATCH 0/2] optimise blk_try_enter_queue()

Kill extra rcu_read_lock/unlock() pair in blk_try_enter_queue().
Testing with io_uring (high batching) with nullblk:

Before:
3.20%  io_uring  [kernel.vmlinux]  [k] __rcu_read_unlock
3.05%  io_uring  [kernel.vmlinux]  [k] __rcu_read_lock

After:
2.52%  io_uring  [kernel.vmlinux]  [k] __rcu_read_unlock
2.28%  io_uring  [kernel.vmlinux]  [k] __rcu_read_lock

Doesn't necessarily translates into 1.4% perfofrmance improvement
but nice to have.

Pavel Begunkov (2):
  percpu_ref: percpu_ref_tryget_live() version holding RCU
  block: kill extra rcu lock/unlock in queue enter

 block/blk-core.c                |  2 +-
 include/linux/percpu-refcount.h | 31 +++++++++++++++++++++----------
 2 files changed, 22 insertions(+), 11 deletions(-)

-- 
2.33.1