Commit | Line | Data |
---|---|---|
cbb5901b JA |
1 | Queue sysfs files |
2 | ================= | |
3 | ||
4 | This text file will detail the queue files that are located in the sysfs tree | |
5 | for each block device. Note that stacked devices typically do not export | |
6 | any settings, since their queue merely functions are a remapping target. | |
7 | These files are the ones found in the /sys/block/xxx/queue/ directory. | |
8 | ||
9 | Files denoted with a RO postfix are readonly and the RW postfix means | |
10 | read-write. | |
11 | ||
4004e90c NJ |
12 | add_random (RW) |
13 | ---------------- | |
db4ced14 | 14 | This file allows to turn off the disk entropy contribution. Default |
4004e90c NJ |
15 | value of this file is '1'(on). |
16 | ||
17 | discard_granularity (RO) | |
18 | ----------------------- | |
19 | This shows the size of internal allocation of the device in bytes, if | |
20 | reported by the device. A value of '0' means device does not support | |
21 | the discard functionality. | |
22 | ||
0034af03 | 23 | discard_max_hw_bytes (RO) |
4004e90c NJ |
24 | ---------------------- |
25 | Devices that support discard functionality may have internal limits on | |
26 | the number of bytes that can be trimmed or unmapped in a single operation. | |
27 | The discard_max_bytes parameter is set by the device driver to the maximum | |
28 | number of bytes that can be discarded in a single operation. Discard | |
29 | requests issued to the device must not exceed this limit. A discard_max_bytes | |
30 | value of 0 means that the device does not support discard functionality. | |
31 | ||
0034af03 JA |
32 | discard_max_bytes (RW) |
33 | ---------------------- | |
34 | While discard_max_hw_bytes is the hardware limit for the device, this | |
35 | setting is the software limit. Some devices exhibit large latencies when | |
36 | large discards are issued, setting this value lower will make Linux issue | |
37 | smaller discards and potentially help reduce latencies induced by large | |
38 | discard operations. | |
39 | ||
4004e90c NJ |
40 | discard_zeroes_data (RO) |
41 | ------------------------ | |
42 | When read, this file will show if the discarded block are zeroed by the | |
43 | device or not. If its value is '1' the blocks are zeroed otherwise not. | |
44 | ||
cbb5901b JA |
45 | hw_sector_size (RO) |
46 | ------------------- | |
47 | This is the hardware sector size of the device, in bytes. | |
48 | ||
4004e90c NJ |
49 | iostats (RW) |
50 | ------------- | |
51 | This file is used to control (on/off) the iostats accounting of the | |
52 | disk. | |
53 | ||
54 | logical_block_size (RO) | |
55 | ----------------------- | |
56 | This is the logcal block size of the device, in bytes. | |
57 | ||
cbb5901b JA |
58 | max_hw_sectors_kb (RO) |
59 | ---------------------- | |
60 | This is the maximum number of kilobytes supported in a single data transfer. | |
61 | ||
4004e90c NJ |
62 | max_integrity_segments (RO) |
63 | --------------------------- | |
64 | When read, this file shows the max limit of integrity segments as | |
65 | set by block layer which a hardware controller can handle. | |
66 | ||
cbb5901b JA |
67 | max_sectors_kb (RW) |
68 | ------------------- | |
69 | This is the maximum number of kilobytes that the block layer will allow | |
70 | for a filesystem request. Must be smaller than or equal to the maximum | |
71 | size allowed by the hardware. | |
72 | ||
4004e90c NJ |
73 | max_segments (RO) |
74 | ----------------- | |
75 | Maximum number of segments of the device. | |
76 | ||
77 | max_segment_size (RO) | |
78 | --------------------- | |
79 | Maximum segment size of the device. | |
80 | ||
81 | minimum_io_size (RO) | |
82 | -------------------- | |
db4ced14 | 83 | This is the smallest preferred IO size reported by the device. |
4004e90c | 84 | |
cbb5901b JA |
85 | nomerges (RW) |
86 | ------------- | |
488991e2 AB |
87 | This enables the user to disable the lookup logic involved with IO |
88 | merging requests in the block layer. By default (0) all merges are | |
89 | enabled. When set to 1 only simple one-hit merges will be tried. When | |
90 | set to 2 no merge algorithms will be tried (including one-hit or more | |
91 | complex tree/hash lookups). | |
cbb5901b JA |
92 | |
93 | nr_requests (RW) | |
94 | ---------------- | |
95 | This controls how many requests may be allocated in the block layer for | |
96 | read or write requests. Note that the total allocated number may be twice | |
97 | this amount, since it applies only to reads or writes (not the accumulated | |
98 | sum). | |
99 | ||
a051661c TH |
100 | To avoid priority inversion through request starvation, a request |
101 | queue maintains a separate request pool per each cgroup when | |
102 | CONFIG_BLK_CGROUP is enabled, and this parameter applies to each such | |
103 | per-block-cgroup request pool. IOW, if there are N block cgroups, | |
f884ab15 | 104 | each request queue may have up to N request pools, each independently |
a051661c TH |
105 | regulated by nr_requests. |
106 | ||
4004e90c NJ |
107 | optimal_io_size (RO) |
108 | -------------------- | |
db4ced14 | 109 | This is the optimal IO size reported by the device. |
4004e90c NJ |
110 | |
111 | physical_block_size (RO) | |
112 | ------------------------ | |
113 | This is the physical block size of device, in bytes. | |
114 | ||
cbb5901b JA |
115 | read_ahead_kb (RW) |
116 | ------------------ | |
117 | Maximum number of kilobytes to read-ahead for filesystems on this block | |
118 | device. | |
119 | ||
4004e90c NJ |
120 | rotational (RW) |
121 | --------------- | |
122 | This file is used to stat if the device is of rotational type or | |
123 | non-rotational type. | |
124 | ||
cbb5901b JA |
125 | rq_affinity (RW) |
126 | ---------------- | |
5757a6d7 DW |
127 | If this option is '1', the block layer will migrate request completions to the |
128 | cpu "group" that originally submitted the request. For some workloads this | |
129 | provides a significant reduction in CPU cycles due to caching effects. | |
130 | ||
131 | For storage configurations that need to maximize distribution of completion | |
132 | processing setting this option to '2' forces the completion to run on the | |
133 | requesting cpu (bypassing the "group" aggregation logic). | |
cbb5901b JA |
134 | |
135 | scheduler (RW) | |
136 | -------------- | |
137 | When read, this file will display the current and available IO schedulers | |
138 | for this block device. The currently active IO scheduler will be enclosed | |
139 | in [] brackets. Writing an IO scheduler name to this file will switch | |
140 | control of this block device to that new IO scheduler. Note that writing | |
141 | an IO scheduler name to this file will attempt to load that IO scheduler | |
142 | module, if it isn't already present in the system. | |
143 | ||
144 | ||
145 | ||
146 | Jens Axboe <jens.axboe@oracle.com>, February 2009 |