Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
1Queue sysfs files
2=================
3
4This text file will detail the queue files that are located in the sysfs tree
5for each block device. Note that stacked devices typically do not export
6any settings, since their queue merely functions are a remapping target.
7These files are the ones found in the /sys/block/xxx/queue/ directory.
8
9Files denoted with a RO postfix are readonly and the RW postfix means
10read-write.
11
12hw_sector_size (RO)
13-------------------
14This is the hardware sector size of the device, in bytes.
15
16max_hw_sectors_kb (RO)
17----------------------
18This is the maximum number of kilobytes supported in a single data transfer.
19
20max_sectors_kb (RW)
21-------------------
22This is the maximum number of kilobytes that the block layer will allow
23for a filesystem request. Must be smaller than or equal to the maximum
24size allowed by the hardware.
25
26nomerges (RW)
27-------------
28This enables the user to disable the lookup logic involved with IO
29merging requests in the block layer. By default (0) all merges are
30enabled. When set to 1 only simple one-hit merges will be tried. When
31set to 2 no merge algorithms will be tried (including one-hit or more
32complex tree/hash lookups).
33
34nr_requests (RW)
35----------------
36This controls how many requests may be allocated in the block layer for
37read or write requests. Note that the total allocated number may be twice
38this amount, since it applies only to reads or writes (not the accumulated
39sum).
40
41read_ahead_kb (RW)
42------------------
43Maximum number of kilobytes to read-ahead for filesystems on this block
44device.
45
46rq_affinity (RW)
47----------------
48If this option is enabled, the block layer will migrate request completions
49to the CPU that originally submitted the request. For some workloads
50this provides a significant reduction in CPU cycles due to caching effects.
51
52scheduler (RW)
53--------------
54When read, this file will display the current and available IO schedulers
55for this block device. The currently active IO scheduler will be enclosed
56in [] brackets. Writing an IO scheduler name to this file will switch
57control of this block device to that new IO scheduler. Note that writing
58an IO scheduler name to this file will attempt to load that IO scheduler
59module, if it isn't already present in the system.
60
61
62
63Jens Axboe <jens.axboe@oracle.com>, February 2009