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authorLinus Torvalds <torvalds@linux-foundation.org>2013-12-24 10:06:03 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-12-24 10:06:03 -0800
commitc5fdd531b593205a0e8c1ab253dd85b764fd0ecb (patch)
tree9117fff70e04077117d447f3eafd9b9d0d1a1041 /Documentation
parent70e672fa7376d45e262119bda3e1a301e519d4c3 (diff)
parentfc1bc35443741e132dd0118e8dbac53f69a6f76e (diff)
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Merge branch 'for-linus' of git://git.kernel.dk/linux-block
Pull block fixes from Jens Axboe: - fix for a memory leak on certain unplug events - a collection of bcache fixes from Kent and Nicolas - a few null_blk fixes and updates form Matias - a marking of static of functions in the stec pci-e driver * 'for-linus' of git://git.kernel.dk/linux-block: null_blk: support submit_queues on use_per_node_hctx null_blk: set use_per_node_hctx param to false null_blk: corrections to documentation null_blk: warning on ignored submit_queues param null_blk: refactor init and init errors code paths null_blk: documentation null_blk: mem garbage on NUMA systems during init drivers: block: Mark the functions as static in skd_main.c bcache: New writeback PD controller bcache: bugfix for race between moving_gc and bucket_invalidate bcache: fix for gc and writeback race bcache: bugfix - moving_gc now moves only correct buckets bcache: fix for gc crashing when no sectors are used bcache: Fix heap_peek() macro bcache: Fix for can_attach_cache() bcache: Fix dirty_data accounting bcache: Use uninterruptible sleep in writeback bcache: kthread don't set writeback task to INTERUPTIBLE block: fix memory leaks on unplugging block device bcache: fix sparse non static symbol warning
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/block/null_blk.txt72
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diff --git a/Documentation/block/null_blk.txt b/Documentation/block/null_blk.txt
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+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.
+
+irq_mode=[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 irq_mode=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.
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