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Commit | Line | Data |
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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 | ||
005411ea JL |
17 | dax (RO) |
18 | -------- | |
19 | This file indicates whether the device supports Direct Access (DAX), | |
20 | used by CPU-addressable storage to bypass the pagecache. It shows '1' | |
21 | if true, '0' if not. | |
22 | ||
4004e90c NJ |
23 | discard_granularity (RO) |
24 | ----------------------- | |
25 | This shows the size of internal allocation of the device in bytes, if | |
26 | reported by the device. A value of '0' means device does not support | |
27 | the discard functionality. | |
28 | ||
0034af03 | 29 | discard_max_hw_bytes (RO) |
4004e90c NJ |
30 | ---------------------- |
31 | Devices that support discard functionality may have internal limits on | |
32 | the number of bytes that can be trimmed or unmapped in a single operation. | |
33 | The discard_max_bytes parameter is set by the device driver to the maximum | |
34 | number of bytes that can be discarded in a single operation. Discard | |
35 | requests issued to the device must not exceed this limit. A discard_max_bytes | |
36 | value of 0 means that the device does not support discard functionality. | |
37 | ||
0034af03 JA |
38 | discard_max_bytes (RW) |
39 | ---------------------- | |
40 | While discard_max_hw_bytes is the hardware limit for the device, this | |
41 | setting is the software limit. Some devices exhibit large latencies when | |
42 | large discards are issued, setting this value lower will make Linux issue | |
43 | smaller discards and potentially help reduce latencies induced by large | |
44 | discard operations. | |
45 | ||
cbb5901b JA |
46 | hw_sector_size (RO) |
47 | ------------------- | |
48 | This is the hardware sector size of the device, in bytes. | |
49 | ||
005411ea JL |
50 | io_poll (RW) |
51 | ------------ | |
7158339d JM |
52 | When read, this file shows whether polling is enabled (1) or disabled |
53 | (0). Writing '0' to this file will disable polling for this device. | |
54 | Writing any non-zero value will enable this feature. | |
005411ea | 55 | |
10e6246e JA |
56 | io_poll_delay (RW) |
57 | ------------------ | |
58 | If polling is enabled, this controls what kind of polling will be | |
59 | performed. It defaults to -1, which is classic polling. In this mode, | |
60 | the CPU will repeatedly ask for completions without giving up any time. | |
61 | If set to 0, a hybrid polling mode is used, where the kernel will attempt | |
62 | to make an educated guess at when the IO will complete. Based on this | |
63 | guess, the kernel will put the process issuing IO to sleep for an amount | |
64 | of time, before entering a classic poll loop. This mode might be a | |
65 | little slower than pure classic polling, but it will be more efficient. | |
66 | If set to a value larger than 0, the kernel will put the process issuing | |
f9824952 | 67 | IO to sleep for this amount of microseconds before entering classic |
10e6246e JA |
68 | polling. |
69 | ||
bb351aba WZ |
70 | io_timeout (RW) |
71 | --------------- | |
72 | io_timeout is the request timeout in milliseconds. If a request does not | |
73 | complete in this time then the block driver timeout handler is invoked. | |
74 | That timeout handler can decide to retry the request, to fail it or to start | |
75 | a device recovery strategy. | |
76 | ||
4004e90c NJ |
77 | iostats (RW) |
78 | ------------- | |
79 | This file is used to control (on/off) the iostats accounting of the | |
80 | disk. | |
81 | ||
82 | logical_block_size (RO) | |
83 | ----------------------- | |
141fd28c | 84 | This is the logical block size of the device, in bytes. |
4004e90c | 85 | |
cbb5901b JA |
86 | max_hw_sectors_kb (RO) |
87 | ---------------------- | |
88 | This is the maximum number of kilobytes supported in a single data transfer. | |
89 | ||
4004e90c NJ |
90 | max_integrity_segments (RO) |
91 | --------------------------- | |
92 | When read, this file shows the max limit of integrity segments as | |
93 | set by block layer which a hardware controller can handle. | |
94 | ||
cbb5901b JA |
95 | max_sectors_kb (RW) |
96 | ------------------- | |
97 | This is the maximum number of kilobytes that the block layer will allow | |
98 | for a filesystem request. Must be smaller than or equal to the maximum | |
99 | size allowed by the hardware. | |
100 | ||
4004e90c NJ |
101 | max_segments (RO) |
102 | ----------------- | |
103 | Maximum number of segments of the device. | |
104 | ||
105 | max_segment_size (RO) | |
106 | --------------------- | |
107 | Maximum segment size of the device. | |
108 | ||
109 | minimum_io_size (RO) | |
110 | -------------------- | |
db4ced14 | 111 | This is the smallest preferred IO size reported by the device. |
4004e90c | 112 | |
cbb5901b JA |
113 | nomerges (RW) |
114 | ------------- | |
488991e2 AB |
115 | This enables the user to disable the lookup logic involved with IO |
116 | merging requests in the block layer. By default (0) all merges are | |
117 | enabled. When set to 1 only simple one-hit merges will be tried. When | |
118 | set to 2 no merge algorithms will be tried (including one-hit or more | |
119 | complex tree/hash lookups). | |
cbb5901b JA |
120 | |
121 | nr_requests (RW) | |
122 | ---------------- | |
123 | This controls how many requests may be allocated in the block layer for | |
124 | read or write requests. Note that the total allocated number may be twice | |
125 | this amount, since it applies only to reads or writes (not the accumulated | |
126 | sum). | |
127 | ||
a051661c TH |
128 | To avoid priority inversion through request starvation, a request |
129 | queue maintains a separate request pool per each cgroup when | |
130 | CONFIG_BLK_CGROUP is enabled, and this parameter applies to each such | |
131 | per-block-cgroup request pool. IOW, if there are N block cgroups, | |
f884ab15 | 132 | each request queue may have up to N request pools, each independently |
a051661c TH |
133 | regulated by nr_requests. |
134 | ||
4004e90c NJ |
135 | optimal_io_size (RO) |
136 | -------------------- | |
db4ced14 | 137 | This is the optimal IO size reported by the device. |
4004e90c NJ |
138 | |
139 | physical_block_size (RO) | |
140 | ------------------------ | |
141 | This is the physical block size of device, in bytes. | |
142 | ||
cbb5901b JA |
143 | read_ahead_kb (RW) |
144 | ------------------ | |
145 | Maximum number of kilobytes to read-ahead for filesystems on this block | |
146 | device. | |
147 | ||
4004e90c NJ |
148 | rotational (RW) |
149 | --------------- | |
150 | This file is used to stat if the device is of rotational type or | |
151 | non-rotational type. | |
152 | ||
cbb5901b JA |
153 | rq_affinity (RW) |
154 | ---------------- | |
5757a6d7 DW |
155 | If this option is '1', the block layer will migrate request completions to the |
156 | cpu "group" that originally submitted the request. For some workloads this | |
157 | provides a significant reduction in CPU cycles due to caching effects. | |
158 | ||
159 | For storage configurations that need to maximize distribution of completion | |
160 | processing setting this option to '2' forces the completion to run on the | |
161 | requesting cpu (bypassing the "group" aggregation logic). | |
cbb5901b JA |
162 | |
163 | scheduler (RW) | |
164 | -------------- | |
165 | When read, this file will display the current and available IO schedulers | |
166 | for this block device. The currently active IO scheduler will be enclosed | |
167 | in [] brackets. Writing an IO scheduler name to this file will switch | |
168 | control of this block device to that new IO scheduler. Note that writing | |
169 | an IO scheduler name to this file will attempt to load that IO scheduler | |
170 | module, if it isn't already present in the system. | |
171 | ||
93e9d8e8 JA |
172 | write_cache (RW) |
173 | ---------------- | |
174 | When read, this file will display whether the device has write back | |
175 | caching enabled or not. It will return "write back" for the former | |
176 | case, and "write through" for the latter. Writing to this file can | |
177 | change the kernels view of the device, but it doesn't alter the | |
178 | device state. This means that it might not be safe to toggle the | |
179 | setting from "write back" to "write through", since that will also | |
180 | eliminate cache flushes issued by the kernel. | |
cbb5901b | 181 | |
005411ea JL |
182 | write_same_max_bytes (RO) |
183 | ------------------------- | |
184 | This is the number of bytes the device can write in a single write-same | |
185 | command. A value of '0' means write-same is not supported by this | |
186 | device. | |
187 | ||
87760e5e JA |
188 | wb_lat_usec (RW) |
189 | ---------------- | |
190 | If the device is registered for writeback throttling, then this file shows | |
191 | the target minimum read latency. If this latency is exceeded in a given | |
192 | window of time (see wb_window_usec), then the writeback throttling will start | |
80e091d1 JA |
193 | scaling back writes. Writing a value of '0' to this file disables the |
194 | feature. Writing a value of '-1' to this file resets the value to the | |
195 | default setting. | |
87760e5e | 196 | |
297e3d85 SL |
197 | throttle_sample_time (RW) |
198 | ------------------------- | |
199 | This is the time window that blk-throttle samples data, in millisecond. | |
200 | blk-throttle makes decision based on the samplings. Lower time means cgroups | |
201 | have more smooth throughput, but higher CPU overhead. This exists only when | |
202 | CONFIG_BLK_DEV_THROTTLING_LOW is enabled. | |
cbb5901b | 203 | |
f9824952 DLM |
204 | zoned (RO) |
205 | ---------- | |
206 | This indicates if the device is a zoned block device and the zone model of the | |
207 | device if it is indeed zoned. The possible values indicated by zoned are | |
208 | "none" for regular block devices and "host-aware" or "host-managed" for zoned | |
209 | block devices. The characteristics of host-aware and host-managed zoned block | |
210 | devices are described in the ZBC (Zoned Block Commands) and ZAC | |
211 | (Zoned Device ATA Command Set) standards. These standards also define the | |
212 | "drive-managed" zone model. However, since drive-managed zoned block devices | |
213 | do not support zone commands, they will be treated as regular block devices | |
214 | and zoned will report "none". | |
215 | ||
216 | nr_zones (RO) | |
217 | ------------- | |
218 | For zoned block devices (zoned attribute indicating "host-managed" or | |
219 | "host-aware"), this indicates the total number of zones of the device. | |
220 | This is always 0 for regular block devices. | |
221 | ||
222 | chunk_sectors (RO) | |
223 | ------------------ | |
224 | This has different meaning depending on the type of the block device. | |
225 | For a RAID device (dm-raid), chunk_sectors indicates the size in 512B sectors | |
226 | of the RAID volume stripe segment. For a zoned block device, either host-aware | |
227 | or host-managed, chunk_sectors indicates the size in 512B sectors of the zones | |
228 | of the device, with the eventual exception of the last zone of the device which | |
229 | may be smaller. | |
230 | ||
cbb5901b | 231 | Jens Axboe <jens.axboe@oracle.com>, February 2009 |