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Commit 04c56957 authored by André Almeida's avatar André Almeida Committed by Jens Axboe
Browse files

docs: block: null_blk: enhance document style 



Use proper ReST syntax for chapters. Add more information to enhance
standardization in the file and to make the rendering more homogeneous.
Add a SPDX identifier. Mark single-queue mode as deprecated.

Signed-off-by: default avatarAndré Almeida <andrealmeid@collabora.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 7c1ee704

Documentation/block/null_blk.rst

+18 −15
Original line number Diff line number Diff line 
.. SPDX-License-Identifier: GPL-2.0



========================

Null block device driver

========================



1. Overview

===========

Overview

========



The null block device (/dev/nullb*) is used for benchmarking the various

The null block device (``/dev/nullb*``) is used for benchmarking the various

block-layer implementations. It emulates a block device of X gigabytes in size.

The following instances are possible:



  Single-queue block-layer



    - Request-based.

    - Single submission queue per device.

    - Implements IO scheduling algorithms (CFQ, Deadline, noop).

It does not execute any read/write operation, just mark them as complete in

the request queue. The following instances are possible:



  Multi-queue block-layer
@@ -27,15 +24,15 @@ The following instances are possible: 


All of them have a completion queue for each core in the system.



2. Module parameters applicable for all instances

=================================================

Module parameters

=================



queue_mode=[0-2]: Default: 2-Multi-queue

  Selects which block-layer the module should instantiate with.



  =  ============

  0  Bio-based

  1  Single-queue

  1  Single-queue (deprecated)

  2  Multi-queue

  =  ============
@@ -67,7 +64,7 @@ irqmode=[0-2]: Default: 1-Soft-irq 
completion_nsec=[ns]: Default: 10,000ns

  Combined with irqmode=2 (timer). The time each completion event must wait.



submit_queues=[1..nr_cpus]:

submit_queues=[1..nr_cpus]: Default: 1

  The number of submission queues attached to the device driver. If unset, it

  defaults to 1. For multi-queue, it is ignored when use_per_node_hctx module

  parameter is 1.
@@ -75,9 +72,11 @@ submit_queues=[1..nr_cpus]: 
hw_queue_depth=[0..qdepth]: Default: 64

  The hardware queue depth of the device.



III: Multi-queue specific parameters

Multi-queue specific parameters

-------------------------------



use_per_node_hctx=[0/1]: Default: 0

  Number of hardware context queues.



  =  =====================================================================

  0  The number of submit queues are set to the value of the submit_queues
@@ -87,6 +86,7 @@ use_per_node_hctx=[0/1]: Default: 0 
  =  =====================================================================



no_sched=[0/1]: Default: 0

  Enable/disable the io scheduler.



  =  ======================================

  0  nullb* use default blk-mq io scheduler
@@ -94,6 +94,7 @@ no_sched=[0/1]: Default: 0 
  =  ======================================



blocking=[0/1]: Default: 0

  Blocking behavior of the request queue.



  =  ===============================================================

  0  Register as a non-blocking blk-mq driver device.
@@ -103,6 +104,7 @@ blocking=[0/1]: Default: 0 
  =  ===============================================================



shared_tags=[0/1]: Default: 0

  Sharing tags between devices.



  =  ================================================================

  0  Tag set is not shared.
@@ -111,6 +113,7 @@ shared_tags=[0/1]: Default: 0 
  =  ================================================================



zoned=[0/1]: Default: 0

  Device is a random-access or a zoned block device.



  =  ======================================================================

  0  Block device is exposed as a random-access block device.