linux-kernel - [PATCH 00/17] ublk: avoid accessing ublk_queue to handle ublksrv_io

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Message-ID: <20250918014953.297897-1-csander@purestorage.com>
Date: Wed, 17 Sep 2025 19:49:36 -0600
From: Caleb Sander Mateos <csander@...estorage.com>
To: Ming Lei <ming.lei@...hat.com>,
	Jens Axboe <axboe@...nel.dk>
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Caleb Sander Mateos <csander@...estorage.com>
Subject: [PATCH 00/17] ublk: avoid accessing ublk_queue to handle ublksrv_io_cmd

For ublk servers with many ublk queues, accessing the ublk_queue in
ublk_ch_uring_cmd_local() and the functions it calls is a frequent cache miss.
The ublk_queue is only accessed for its q_depth and flags, which are also
available on ublk_device. And ublk_device is already accessed for nr_hw_queues,
so it will already be cached. Unfortunately, the UBLK_IO_NEED_GET_DATA path
still needs to access the ublk_queue for io_cmd_buf, so it's not possible to
avoid accessing the ublk_queue there. (Allocating a single io_cmd_buf for all of
a ublk_device's I/Os could be done in the future.) At least we can optimize
UBLK_IO_FETCH_REQ, UBLK_IO_COMMIT_AND_FETCH_REQ, UBLK_IO_REGISTER_IO_BUF, and
UBLK_IO_UNREGISTER_IO_BUF.
Using only the ublk_device and not the ublk_queue in ublk_dispatch_req() is also
possible, but left for a future change.

Caleb Sander Mateos (17):
  ublk: remove ubq check in ublk_check_and_get_req()
  ublk: don't pass q_id to ublk_queue_cmd_buf_size()
  ublk: don't pass ublk_queue to __ublk_fail_req()
  ublk: add helpers to check ublk_device flags
  ublk: don't dereference ublk_queue in ublk_ch_uring_cmd_local()
  ublk: don't dereference ublk_queue in ublk_check_and_get_req()
  ublk: pass ublk_device to ublk_register_io_buf()
  ublk: don't access ublk_queue in ublk_register_io_buf()
  ublk: don't access ublk_queue in ublk_daemon_register_io_buf()
  ublk: pass q_id and tag to __ublk_check_and_get_req()
  ublk: don't access ublk_queue in ublk_check_fetch_buf()
  ublk: don't access ublk_queue in ublk_config_io_buf()
  ublk: don't pass ublk_queue to ublk_fetch()
  ublk: don't access ublk_queue in ublk_check_commit_and_fetch()
  ublk: don't access ublk_queue in ublk_need_complete_req()
  ublk: pass ublk_io to __ublk_complete_rq()
  ublk: don't access ublk_queue in ublk_unmap_io()

 drivers/block/ublk_drv.c | 155 +++++++++++++++++++++++----------------
 1 file changed, 93 insertions(+), 62 deletions(-)

-- 
2.45.2