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: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
André Almeida 2019-09-11 11:46:34 -03:00 committed by Jens Axboe
parent 7c1ee704a1
commit 04c56957eb
1 changed files with 18 additions and 15 deletions

View File

@ -1,19 +1,16 @@
.. 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.