linux-kernel - [PATCH RFC v2 0/5] blk-mq-sched: support request batch dispatching for sq elevator

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Message-Id: <20250614092528.2352680-1-yukuai1@huaweicloud.com>
Date: Sat, 14 Jun 2025 17:25:23 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: ming.lei@...hat.com,
	yukuai3@...wei.com,
	tj@...nel.org,
	josef@...icpanda.com,
	axboe@...nel.dk
Cc: linux-block@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH RFC v2 0/5] blk-mq-sched: support request batch dispatching for sq elevator

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

Before this patch, each dispatch context will hold a global lock to
dispatch one request at a time, which introduce intense lock competition:

lock
ops.dispatch_request
unlock

Hence support dispatch a batch of requests while holding the lock to
reduce lock contention.

nullblk setup:
modprobe null_blk nr_devices=0 &&
    udevadm settle &&
    cd /sys/kernel/config/nullb &&
    mkdir nullb0 &&
    cd nullb0 &&
    echo 0 > completion_nsec &&
    echo 512 > blocksize &&
    echo 0 > home_node &&
    echo 0 > irqmode &&
    echo 128 > submit_queues &&
    echo 1024 > hw_queue_depth &&
    echo 1024 > size &&
    echo 0 > memory_backed &&
    echo 2 > queue_mode &&
    echo 1 > power ||
    exit $?

Test script:
fio -filename=/dev/$disk -name=test -rw=randwrite -bs=4k -iodepth=32 \
  -numjobs=16 --iodepth_batch_submit=8 --iodepth_batch_complete=8 \
  -direct=1 -ioengine=io_uring -group_reporting -time_based -runtime=30

Test result(elevator is deadline): iops
|                 | null_blk | scsi hdd |
| --------------- | -------- | -------- |
| before this set | 263k     | 24       |
| after this set  | 475k     | 272      |

Yu Kuai (5):
  elevator: introduce global lock for sq_shared elevator
  mq-deadline: switch to use elevator lock
  block, bfq: 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/bfq-cgroup.c   |   4 +-
 block/bfq-iosched.c  |  53 ++++------
 block/bfq-iosched.h  |   2 +-
 block/blk-mq-sched.c | 226 +++++++++++++++++++++++++++++--------------
 block/blk-mq.c       |   5 +-
 block/blk-mq.h       |  21 ++++
 block/elevator.c     |   1 +
 block/elevator.h     |  61 +++++++++++-
 block/mq-deadline.c  |  58 +++++------
 9 files changed, 282 insertions(+), 149 deletions(-)

-- 
2.39.2