linux-kernel - [PATCH v2 0/2] optimise blk_try_enter

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Date:   Thu, 21 Oct 2021 14:30:50 +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 v2 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.

v2: rcu_read_lock_held() warning (Tejun)

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 | 33 +++++++++++++++++++++++----------
 2 files changed, 24 insertions(+), 11 deletions(-)

-- 
2.33.1