Commit | Line | Data |
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fd2ed4d2 MP |
1 | DM statistics |
2 | ============= | |
3 | ||
4 | Device Mapper supports the collection of I/O statistics on user-defined | |
5 | regions of a DM device. If no regions are defined no statistics are | |
6 | collected so there isn't any performance impact. Only bio-based DM | |
7 | devices are currently supported. | |
8 | ||
9 | Each user-defined region specifies a starting sector, length and step. | |
10 | Individual statistics will be collected for each step-sized area within | |
11 | the range specified. | |
12 | ||
13 | The I/O statistics counters for each step-sized area of a region are | |
14 | in the same format as /sys/block/*/stat or /proc/diskstats (see: | |
15 | Documentation/iostats.txt). But two extra counters (12 and 13) are | |
16 | provided: total time spent reading and writing in milliseconds. All | |
17 | these counters may be accessed by sending the @stats_print message to | |
18 | the appropriate DM device via dmsetup. | |
19 | ||
20 | Each region has a corresponding unique identifier, which we call a | |
21 | region_id, that is assigned when the region is created. The region_id | |
22 | must be supplied when querying statistics about the region, deleting the | |
23 | region, etc. Unique region_ids enable multiple userspace programs to | |
24 | request and process statistics for the same DM device without stepping | |
25 | on each other's data. | |
26 | ||
27 | The creation of DM statistics will allocate memory via kmalloc or | |
28 | fallback to using vmalloc space. At most, 1/4 of the overall system | |
29 | memory may be allocated by DM statistics. The admin can see how much | |
30 | memory is used by reading | |
31 | /sys/module/dm_mod/parameters/stats_current_allocated_bytes | |
32 | ||
33 | Messages | |
34 | ======== | |
35 | ||
36 | @stats_create <range> <step> [<program_id> [<aux_data>]] | |
37 | ||
38 | Create a new region and return the region_id. | |
39 | ||
40 | <range> | |
41 | "-" - whole device | |
42 | "<start_sector>+<length>" - a range of <length> 512-byte sectors | |
43 | starting with <start_sector>. | |
44 | ||
45 | <step> | |
46 | "<area_size>" - the range is subdivided into areas each containing | |
47 | <area_size> sectors. | |
48 | "/<number_of_areas>" - the range is subdivided into the specified | |
49 | number of areas. | |
50 | ||
51 | <program_id> | |
52 | An optional parameter. A name that uniquely identifies | |
53 | the userspace owner of the range. This groups ranges together | |
54 | so that userspace programs can identify the ranges they | |
55 | created and ignore those created by others. | |
56 | The kernel returns this string back in the output of | |
57 | @stats_list message, but it doesn't use it for anything else. | |
58 | ||
59 | <aux_data> | |
60 | An optional parameter. A word that provides auxiliary data | |
61 | that is useful to the client program that created the range. | |
62 | The kernel returns this string back in the output of | |
63 | @stats_list message, but it doesn't use this value for anything. | |
64 | ||
65 | @stats_delete <region_id> | |
66 | ||
67 | Delete the region with the specified id. | |
68 | ||
69 | <region_id> | |
70 | region_id returned from @stats_create | |
71 | ||
72 | @stats_clear <region_id> | |
73 | ||
74 | Clear all the counters except the in-flight i/o counters. | |
75 | ||
76 | <region_id> | |
77 | region_id returned from @stats_create | |
78 | ||
79 | @stats_list [<program_id>] | |
80 | ||
81 | List all regions registered with @stats_create. | |
82 | ||
83 | <program_id> | |
84 | An optional parameter. | |
85 | If this parameter is specified, only matching regions | |
86 | are returned. | |
87 | If it is not specified, all regions are returned. | |
88 | ||
89 | Output format: | |
90 | <region_id>: <start_sector>+<length> <step> <program_id> <aux_data> | |
91 | ||
92 | @stats_print <region_id> [<starting_line> <number_of_lines>] | |
93 | ||
94 | Print counters for each step-sized area of a region. | |
95 | ||
96 | <region_id> | |
97 | region_id returned from @stats_create | |
98 | ||
99 | <starting_line> | |
100 | The index of the starting line in the output. | |
101 | If omitted, all lines are returned. | |
102 | ||
103 | <number_of_lines> | |
104 | The number of lines to include in the output. | |
105 | If omitted, all lines are returned. | |
106 | ||
107 | Output format for each step-sized area of a region: | |
108 | ||
109 | <start_sector>+<length> counters | |
110 | ||
111 | The first 11 counters have the same meaning as | |
112 | /sys/block/*/stat or /proc/diskstats. | |
113 | ||
114 | Please refer to Documentation/iostats.txt for details. | |
115 | ||
116 | 1. the number of reads completed | |
117 | 2. the number of reads merged | |
118 | 3. the number of sectors read | |
119 | 4. the number of milliseconds spent reading | |
120 | 5. the number of writes completed | |
121 | 6. the number of writes merged | |
122 | 7. the number of sectors written | |
123 | 8. the number of milliseconds spent writing | |
124 | 9. the number of I/Os currently in progress | |
125 | 10. the number of milliseconds spent doing I/Os | |
126 | 11. the weighted number of milliseconds spent doing I/Os | |
127 | ||
128 | Additional counters: | |
129 | 12. the total time spent reading in milliseconds | |
130 | 13. the total time spent writing in milliseconds | |
131 | ||
132 | @stats_print_clear <region_id> [<starting_line> <number_of_lines>] | |
133 | ||
134 | Atomically print and then clear all the counters except the | |
135 | in-flight i/o counters. Useful when the client consuming the | |
136 | statistics does not want to lose any statistics (those updated | |
137 | between printing and clearing). | |
138 | ||
139 | <region_id> | |
140 | region_id returned from @stats_create | |
141 | ||
142 | <starting_line> | |
143 | The index of the starting line in the output. | |
144 | If omitted, all lines are printed and then cleared. | |
145 | ||
146 | <number_of_lines> | |
147 | The number of lines to process. | |
148 | If omitted, all lines are printed and then cleared. | |
149 | ||
150 | @stats_set_aux <region_id> <aux_data> | |
151 | ||
152 | Store auxiliary data aux_data for the specified region. | |
153 | ||
154 | <region_id> | |
155 | region_id returned from @stats_create | |
156 | ||
157 | <aux_data> | |
158 | The string that identifies data which is useful to the client | |
159 | program that created the range. The kernel returns this | |
160 | string back in the output of @stats_list message, but it | |
161 | doesn't use this value for anything. | |
162 | ||
163 | Examples | |
164 | ======== | |
165 | ||
166 | Subdivide the DM device 'vol' into 100 pieces and start collecting | |
167 | statistics on them: | |
168 | ||
169 | dmsetup message vol 0 @stats_create - /100 | |
170 | ||
171 | Set the auxillary data string to "foo bar baz" (the escape for each | |
172 | space must also be escaped, otherwise the shell will consume them): | |
173 | ||
174 | dmsetup message vol 0 @stats_set_aux 0 foo\\ bar\\ baz | |
175 | ||
176 | List the statistics: | |
177 | ||
178 | dmsetup message vol 0 @stats_list | |
179 | ||
180 | Print the statistics: | |
181 | ||
182 | dmsetup message vol 0 @stats_print 0 | |
183 | ||
184 | Delete the statistics: | |
185 | ||
186 | dmsetup message vol 0 @stats_delete 0 |