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| -rw-r--r-- | Documentation/block/null_blk.rst | 33 |
1 files changed, 18 insertions, 15 deletions
diff --git a/Documentation/block/null_blk.rst b/Documentation/block/null_blk.rst index 31451d80783c..edbbab2f12f8 100644 --- a/Documentation/block/null_blk.rst +++ b/Documentation/block/null_blk.rst @@ -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. |