linux-kernel - [PATCH RFC 0/4] blk-mq-sched: support request batch dispatching for sq elevator

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Message-Id: <20250530080355.1138759-1-yukuai1@huaweicloud.com>
Date: Fri, 30 May 2025 16:03:51 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH RFC 0/4] blk-mq-sched: support request batch dispatching for sq elevator

From: Yu Kuai <yukuai3@...wei.com>

Lock contention for sq elevator is quite intense when multiple contexts
are dispatching request, main reason is that a global lock is held and
release for each request:

while
  spin_lock
  disaptch one request
  spin_unlock

This set support request batch dispatching to reduce the lock contention
a bit.

A simple test for null_blk in my VM:
32 job randwrite

| elevator                   | bandwidth Mib/s |
| -------------------------- | --------------- |
| none                       | 813             |
| deadline before this patch | 531             |
| deadline after this patch  | 689             |

The test is one-sided, however, this is just a quick test to show this
set might be meaningful. I'm sending this RFC and want to get some
feedbacks before I continue work on this set.

Noted: do not test bfq for this set, it's not changed yet(like patch 2
for deadline).

Yu Kuai (4):
  elevator: introduce global lock for sq_shared elevator
  mq-deadline: switch to use elevator lock
  blk-mq-sched: refactor __blk_mq_do_dispatch_sched()
  blk-mq-sched: support request batch dispatching for sq elevator

 block/blk-mq-sched.c | 224 +++++++++++++++++++++++++++++--------------
 block/blk-mq.c       |   5 +-
 block/blk-mq.h       |  21 ++++
 block/elevator.c     |   1 +
 block/elevator.h     |  62 +++++++++++-
 block/mq-deadline.c  |  60 +++++-------
 6 files changed, 259 insertions(+), 114 deletions(-)

-- 
2.39.2