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Diffstat (limited to 'Documentation/block/null_blk.txt')
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diff --git a/Documentation/block/null_blk.txt b/Documentation/block/null_blk.txt deleted file mode 100644 index 41f0a3d33bbd..000000000000 --- a/Documentation/block/null_blk.txt +++ /dev/null @@ -1,99 +0,0 @@ -Null block device driver -================================================================================ - -I. Overview - -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). - Multi-queue block-layer - - Request-based. - - Configurable submission queues per device. - No block-layer (Known as bio-based) - - Bio-based. IO requests are submitted directly to the device driver. - - Directly accepts bio data structure and returns them. - -All of them have a completion queue for each core in the system. - -II. Module parameters applicable for all instances: - -queue_mode=[0-2]: Default: 2-Multi-queue - Selects which block-layer the module should instantiate with. - - 0: Bio-based. - 1: Single-queue. - 2: Multi-queue. - -home_node=[0--nr_nodes]: Default: NUMA_NO_NODE - Selects what CPU node the data structures are allocated from. - -gb=[Size in GB]: Default: 250GB - The size of the device reported to the system. - -bs=[Block size (in bytes)]: Default: 512 bytes - The block size reported to the system. - -nr_devices=[Number of devices]: Default: 1 - Number of block devices instantiated. They are instantiated as /dev/nullb0, - etc. - -irqmode=[0-2]: Default: 1-Soft-irq - The completion mode used for completing IOs to the block-layer. - - 0: None. - 1: Soft-irq. Uses IPI to complete IOs across CPU nodes. Simulates the overhead - when IOs are issued from another CPU node than the home the device is - connected to. - 2: Timer: Waits a specific period (completion_nsec) for each IO before - completion. - -completion_nsec=[ns]: Default: 10,000ns - Combined with irqmode=2 (timer). The time each completion event must wait. - -submit_queues=[1..nr_cpus]: - 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. - -hw_queue_depth=[0..qdepth]: Default: 64 - The hardware queue depth of the device. - -III: Multi-queue specific parameters - -use_per_node_hctx=[0/1]: Default: 0 - 0: The number of submit queues are set to the value of the submit_queues - parameter. - 1: The multi-queue block layer is instantiated with a hardware dispatch - queue for each CPU node in the system. - -no_sched=[0/1]: Default: 0 - 0: nullb* use default blk-mq io scheduler. - 1: nullb* doesn't use io scheduler. - -blocking=[0/1]: Default: 0 - 0: Register as a non-blocking blk-mq driver device. - 1: Register as a blocking blk-mq driver device, null_blk will set - the BLK_MQ_F_BLOCKING flag, indicating that it sometimes/always - needs to block in its ->queue_rq() function. - -shared_tags=[0/1]: Default: 0 - 0: Tag set is not shared. - 1: Tag set shared between devices for blk-mq. Only makes sense with - nr_devices > 1, otherwise there's no tag set to share. - -zoned=[0/1]: Default: 0 - 0: Block device is exposed as a random-access block device. - 1: Block device is exposed as a host-managed zoned block device. Requires - CONFIG_BLK_DEV_ZONED. - -zone_size=[MB]: Default: 256 - Per zone size when exposed as a zoned block device. Must be a power of two. - -zone_nr_conv=[nr_conv]: Default: 0 - The number of conventional zones to create when block device is zoned. If - zone_nr_conv >= nr_zones, it will be reduced to nr_zones - 1. |