| 12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576 |
- 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: 2
- 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=[0..nr_cpus]:
- The number of submission queues attached to the device driver. If unset, it
- defaults to 1 on single-queue and bio-based instances. 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.
- use_lightnvm=[0/1]: Default: 0
- Register device with LightNVM. Requires blk-mq to be used.
|
