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Linux/Documentation/admin-guide/cgroup-v1/blkio-controller.rst

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Diff markup

Differences between /Documentation/admin-guide/cgroup-v1/blkio-controller.rst (Version linux-6.12-rc7) and /Documentation/admin-guide/cgroup-v1/blkio-controller.rst (Version linux-5.13.19)


  1 ===================                                 1 ===================
  2 Block IO Controller                                 2 Block IO Controller
  3 ===================                                 3 ===================
  4                                                     4 
  5 Overview                                            5 Overview
  6 ========                                            6 ========
  7 cgroup subsys "blkio" implements the block io       7 cgroup subsys "blkio" implements the block io controller. There seems to be
  8 a need of various kinds of IO control policies      8 a need of various kinds of IO control policies (like proportional BW, max BW)
  9 both at leaf nodes as well as at intermediate       9 both at leaf nodes as well as at intermediate nodes in a storage hierarchy.
 10 Plan is to use the same cgroup based managemen     10 Plan is to use the same cgroup based management interface for blkio controller
 11 and based on user options switch IO policies i     11 and based on user options switch IO policies in the background.
 12                                                    12 
 13 One IO control policy is throttling policy whi     13 One IO control policy is throttling policy which can be used to
 14 specify upper IO rate limits on devices. This      14 specify upper IO rate limits on devices. This policy is implemented in
 15 generic block layer and can be used on leaf no     15 generic block layer and can be used on leaf nodes as well as higher
 16 level logical devices like device mapper.          16 level logical devices like device mapper.
 17                                                    17 
 18 HOWTO                                              18 HOWTO
 19 =====                                              19 =====
 20                                                << 
 21 Throttling/Upper Limit policy                      20 Throttling/Upper Limit policy
 22 -----------------------------                      21 -----------------------------
 23 Enable Block IO controller::                   !!  22 - Enable Block IO controller::
 24                                                    23 
 25         CONFIG_BLK_CGROUP=y                        24         CONFIG_BLK_CGROUP=y
 26                                                    25 
 27 Enable throttling in block layer::             !!  26 - Enable throttling in block layer::
 28                                                    27 
 29         CONFIG_BLK_DEV_THROTTLING=y                28         CONFIG_BLK_DEV_THROTTLING=y
 30                                                    29 
 31 Mount blkio controller (see cgroups.txt, Why a !!  30 - Mount blkio controller (see cgroups.txt, Why are cgroups needed?)::
 32                                                    31 
 33         mount -t cgroup -o blkio none /sys/fs/     32         mount -t cgroup -o blkio none /sys/fs/cgroup/blkio
 34                                                    33 
 35 Specify a bandwidth rate on particular device  !!  34 - Specify a bandwidth rate on particular device for root group. The format
 36 for policy is "<major>:<minor>  <bytes_per_sec !!  35   for policy is "<major>:<minor>  <bytes_per_second>"::
 37                                                    36 
 38         echo "8:16  1048576" > /sys/fs/cgroup/     37         echo "8:16  1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
 39                                                    38 
 40 This will put a limit of 1MB/second on reads h !!  39   Above will put a limit of 1MB/second on reads happening for root group
 41 on device having major/minor number 8:16.      !!  40   on device having major/minor number 8:16.
 42                                                    41 
 43 Run dd to read a file and see if rate is throt !!  42 - Run dd to read a file and see if rate is throttled to 1MB/s or not::
 44                                                    43 
 45         # dd iflag=direct if=/mnt/common/zerof     44         # dd iflag=direct if=/mnt/common/zerofile of=/dev/null bs=4K count=1024
 46         1024+0 records in                          45         1024+0 records in
 47         1024+0 records out                         46         1024+0 records out
 48         4194304 bytes (4.2 MB) copied, 4.0001      47         4194304 bytes (4.2 MB) copied, 4.0001 s, 1.0 MB/s
 49                                                    48 
 50 Limits for writes can be put using blkio.throt !!  49  Limits for writes can be put using blkio.throttle.write_bps_device file.
 51                                                    50 
 52 Hierarchical Cgroups                               51 Hierarchical Cgroups
 53 ====================                               52 ====================
 54                                                    53 
 55 Throttling implements hierarchy support; howev     54 Throttling implements hierarchy support; however,
 56 throttling's hierarchy support is enabled iff      55 throttling's hierarchy support is enabled iff "sane_behavior" is
 57 enabled from cgroup side, which currently is a     56 enabled from cgroup side, which currently is a development option and
 58 not publicly available.                            57 not publicly available.
 59                                                    58 
 60 If somebody created a hierarchy like as follow     59 If somebody created a hierarchy like as follows::
 61                                                    60 
 62                         root                       61                         root
 63                         /  \                       62                         /  \
 64                      test1 test2                   63                      test1 test2
 65                         |                          64                         |
 66                      test3                         65                      test3
 67                                                    66 
 68 Throttling with "sane_behavior" will handle th     67 Throttling with "sane_behavior" will handle the
 69 hierarchy correctly. For throttling, all limit     68 hierarchy correctly. For throttling, all limits apply
 70 to the whole subtree while all statistics are      69 to the whole subtree while all statistics are local to the IOs
 71 directly generated by tasks in that cgroup.        70 directly generated by tasks in that cgroup.
 72                                                    71 
 73 Throttling without "sane_behavior" enabled fro     72 Throttling without "sane_behavior" enabled from cgroup side will
 74 practically treat all groups at same level as      73 practically treat all groups at same level as if it looks like the
 75 following::                                        74 following::
 76                                                    75 
 77                                 pivot              76                                 pivot
 78                              /  /   \  \           77                              /  /   \  \
 79                         root  test1 test2  tes     78                         root  test1 test2  test3
 80                                                    79 
 81 Various user visible config options                80 Various user visible config options
 82 ===================================                81 ===================================
                                                   >>  82 CONFIG_BLK_CGROUP
                                                   >>  83         - Block IO controller.
 83                                                    84 
 84   CONFIG_BLK_CGROUP                            !!  85 CONFIG_BFQ_CGROUP_DEBUG
 85           Block IO controller.                 !!  86         - Debug help. Right now some additional stats file show up in cgroup
 86                                                << 
 87   CONFIG_BFQ_CGROUP_DEBUG                      << 
 88           Debug help. Right now some additiona << 
 89           if this option is enabled.               87           if this option is enabled.
 90                                                    88 
 91   CONFIG_BLK_DEV_THROTTLING                    !!  89 CONFIG_BLK_DEV_THROTTLING
 92           Enable block device throttling suppo !!  90         - Enable block device throttling support in block layer.
 93                                                    91 
 94 Details of cgroup files                            92 Details of cgroup files
 95 =======================                            93 =======================
 96                                                << 
 97 Proportional weight policy files                   94 Proportional weight policy files
 98 --------------------------------                   95 --------------------------------
 99                                                !!  96 - blkio.weight
100   blkio.bfq.weight                             !!  97         - Specifies per cgroup weight. This is default weight of the group
101           Specifies per cgroup weight. This is !!  98           on all the devices until and unless overridden by per device rule.
102           on all the devices until and unless  !!  99           (See blkio.weight_device).
103           (see `blkio.bfq.weight_device` below !! 100           Currently allowed range of weights is from 10 to 1000.
104                                                !! 101 
105           Currently allowed range of weights i !! 102 - blkio.weight_device
106           see Documentation/block/bfq-iosched. !! 103         - One can specify per cgroup per device rules using this interface.
107                                                !! 104           These rules override the default value of group weight as specified
108   blkio.bfq.weight_device                      !! 105           by blkio.weight.
109           Specifies per cgroup per device weig << 
110           weight. For more details, see Docume << 
111                                                   106 
112           Following is the format::               107           Following is the format::
113                                                   108 
114             # echo dev_maj:dev_minor weight >  !! 109             # echo dev_maj:dev_minor weight > blkio.weight_device
115                                                   110 
116           Configure weight=300 on /dev/sdb (8:    111           Configure weight=300 on /dev/sdb (8:16) in this cgroup::
117                                                   112 
118             # echo 8:16 300 > blkio.bfq.weight !! 113             # echo 8:16 300 > blkio.weight_device
119             # cat blkio.bfq.weight_device      !! 114             # cat blkio.weight_device
120             dev     weight                        115             dev     weight
121             8:16    300                           116             8:16    300
122                                                   117 
123           Configure weight=500 on /dev/sda (8:    118           Configure weight=500 on /dev/sda (8:0) in this cgroup::
124                                                   119 
125             # echo 8:0 500 > blkio.bfq.weight_ !! 120             # echo 8:0 500 > blkio.weight_device
126             # cat blkio.bfq.weight_device      !! 121             # cat blkio.weight_device
127             dev     weight                        122             dev     weight
128             8:0     500                           123             8:0     500
129             8:16    300                           124             8:16    300
130                                                   125 
131           Remove specific weight for /dev/sda     126           Remove specific weight for /dev/sda in this cgroup::
132                                                   127 
133             # echo 8:0 0 > blkio.bfq.weight_de !! 128             # echo 8:0 0 > blkio.weight_device
134             # cat blkio.bfq.weight_device      !! 129             # cat blkio.weight_device
135             dev     weight                        130             dev     weight
136             8:16    300                           131             8:16    300
137                                                   132 
138   blkio.time                                   !! 133 - blkio.time
139           Disk time allocated to cgroup per de !! 134         - disk time allocated to cgroup per device in milliseconds. First
140           two fields specify the major and min    135           two fields specify the major and minor number of the device and
141           third field specifies the disk time     136           third field specifies the disk time allocated to group in
142           milliseconds.                           137           milliseconds.
143                                                   138 
144   blkio.sectors                                !! 139 - blkio.sectors
145           Number of sectors transferred to/fro !! 140         - number of sectors transferred to/from disk by the group. First
146           two fields specify the major and min    141           two fields specify the major and minor number of the device and
147           third field specifies the number of     142           third field specifies the number of sectors transferred by the
148           group to/from the device.               143           group to/from the device.
149                                                   144 
150   blkio.io_service_bytes                       !! 145 - blkio.io_service_bytes
151           Number of bytes transferred to/from  !! 146         - Number of bytes transferred to/from the disk by the group. These
152           are further divided by the type of o    147           are further divided by the type of operation - read or write, sync
153           or async. First two fields specify t    148           or async. First two fields specify the major and minor number of the
154           device, third field specifies the op    149           device, third field specifies the operation type and the fourth field
155           specifies the number of bytes.          150           specifies the number of bytes.
156                                                   151 
157   blkio.io_serviced                            !! 152 - blkio.io_serviced
158           Number of IOs (bio) issued to the di !! 153         - Number of IOs (bio) issued to the disk by the group. These
159           are further divided by the type of o    154           are further divided by the type of operation - read or write, sync
160           or async. First two fields specify t    155           or async. First two fields specify the major and minor number of the
161           device, third field specifies the op    156           device, third field specifies the operation type and the fourth field
162           specifies the number of IOs.            157           specifies the number of IOs.
163                                                   158 
164   blkio.io_service_time                        !! 159 - blkio.io_service_time
165           Total amount of time between request !! 160         - Total amount of time between request dispatch and request completion
166           for the IOs done by this cgroup. Thi    161           for the IOs done by this cgroup. This is in nanoseconds to make it
167           meaningful for flash devices too. Fo    162           meaningful for flash devices too. For devices with queue depth of 1,
168           this time represents the actual serv    163           this time represents the actual service time. When queue_depth > 1,
169           that is no longer true as requests m    164           that is no longer true as requests may be served out of order. This
170           may cause the service time for a giv    165           may cause the service time for a given IO to include the service time
171           of multiple IOs when served out of o    166           of multiple IOs when served out of order which may result in total
172           io_service_time > actual time elapse    167           io_service_time > actual time elapsed. This time is further divided by
173           the type of operation - read or writ    168           the type of operation - read or write, sync or async. First two fields
174           specify the major and minor number o    169           specify the major and minor number of the device, third field
175           specifies the operation type and the    170           specifies the operation type and the fourth field specifies the
176           io_service_time in ns.                  171           io_service_time in ns.
177                                                   172 
178   blkio.io_wait_time                           !! 173 - blkio.io_wait_time
179           Total amount of time the IOs for thi !! 174         - Total amount of time the IOs for this cgroup spent waiting in the
180           scheduler queues for service. This c    175           scheduler queues for service. This can be greater than the total time
181           elapsed since it is cumulative io_wa    176           elapsed since it is cumulative io_wait_time for all IOs. It is not a
182           measure of total time the cgroup spe    177           measure of total time the cgroup spent waiting but rather a measure of
183           the wait_time for its individual IOs    178           the wait_time for its individual IOs. For devices with queue_depth > 1
184           this metric does not include the tim    179           this metric does not include the time spent waiting for service once
185           the IO is dispatched to the device b    180           the IO is dispatched to the device but till it actually gets serviced
186           (there might be a time lag here due     181           (there might be a time lag here due to re-ordering of requests by the
187           device). This is in nanoseconds to m    182           device). This is in nanoseconds to make it meaningful for flash
188           devices too. This time is further di    183           devices too. This time is further divided by the type of operation -
189           read or write, sync or async. First     184           read or write, sync or async. First two fields specify the major and
190           minor number of the device, third fi    185           minor number of the device, third field specifies the operation type
191           and the fourth field specifies the i    186           and the fourth field specifies the io_wait_time in ns.
192                                                   187 
193   blkio.io_merged                              !! 188 - blkio.io_merged
194           Total number of bios/requests merged !! 189         - Total number of bios/requests merged into requests belonging to this
195           cgroup. This is further divided by t    190           cgroup. This is further divided by the type of operation - read or
196           write, sync or async.                   191           write, sync or async.
197                                                   192 
198   blkio.io_queued                              !! 193 - blkio.io_queued
199           Total number of requests queued up a !! 194         - Total number of requests queued up at any given instant for this
200           cgroup. This is further divided by t    195           cgroup. This is further divided by the type of operation - read or
201           write, sync or async.                   196           write, sync or async.
202                                                   197 
203   blkio.avg_queue_size                         !! 198 - blkio.avg_queue_size
204           Debugging aid only enabled if CONFIG !! 199         - Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.
205           The average queue size for this cgro    200           The average queue size for this cgroup over the entire time of this
206           cgroup's existence. Queue size sampl    201           cgroup's existence. Queue size samples are taken each time one of the
207           queues of this cgroup gets a timesli    202           queues of this cgroup gets a timeslice.
208                                                   203 
209   blkio.group_wait_time                        !! 204 - blkio.group_wait_time
210           Debugging aid only enabled if CONFIG !! 205         - Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.
211           This is the amount of time the cgrou    206           This is the amount of time the cgroup had to wait since it became busy
212           (i.e., went from 0 to 1 request queu    207           (i.e., went from 0 to 1 request queued) to get a timeslice for one of
213           its queues. This is different from t    208           its queues. This is different from the io_wait_time which is the
214           cumulative total of the amount of ti    209           cumulative total of the amount of time spent by each IO in that cgroup
215           waiting in the scheduler queue. This    210           waiting in the scheduler queue. This is in nanoseconds. If this is
216           read when the cgroup is in a waiting    211           read when the cgroup is in a waiting (for timeslice) state, the stat
217           will only report the group_wait_time    212           will only report the group_wait_time accumulated till the last time it
218           got a timeslice and will not include    213           got a timeslice and will not include the current delta.
219                                                   214 
220   blkio.empty_time                             !! 215 - blkio.empty_time
221           Debugging aid only enabled if CONFIG !! 216         - Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.
222           This is the amount of time a cgroup     217           This is the amount of time a cgroup spends without any pending
223           requests when not being served, i.e.    218           requests when not being served, i.e., it does not include any time
224           spent idling for one of the queues o    219           spent idling for one of the queues of the cgroup. This is in
225           nanoseconds. If this is read when th    220           nanoseconds. If this is read when the cgroup is in an empty state,
226           the stat will only report the empty_    221           the stat will only report the empty_time accumulated till the last
227           time it had a pending request and wi    222           time it had a pending request and will not include the current delta.
228                                                   223 
229   blkio.idle_time                              !! 224 - blkio.idle_time
230           Debugging aid only enabled if CONFIG !! 225         - Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.
231           This is the amount of time spent by     226           This is the amount of time spent by the IO scheduler idling for a
232           given cgroup in anticipation of a be    227           given cgroup in anticipation of a better request than the existing ones
233           from other queues/cgroups. This is i    228           from other queues/cgroups. This is in nanoseconds. If this is read
234           when the cgroup is in an idling stat    229           when the cgroup is in an idling state, the stat will only report the
235           idle_time accumulated till the last     230           idle_time accumulated till the last idle period and will not include
236           the current delta.                      231           the current delta.
237                                                   232 
238   blkio.dequeue                                !! 233 - blkio.dequeue
239           Debugging aid only enabled if CONFIG !! 234         - Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y. This
240           gives the statistics about how many     235           gives the statistics about how many a times a group was dequeued
241           from service tree of the device. Fir    236           from service tree of the device. First two fields specify the major
242           and minor number of the device and t    237           and minor number of the device and third field specifies the number
243           of times a group was dequeued from a    238           of times a group was dequeued from a particular device.
244                                                   239 
245   blkio.*_recursive                            !! 240 - blkio.*_recursive
246           Recursive version of various stats.  !! 241         - Recursive version of various stats. These files show the
247           same information as their non-recurs    242           same information as their non-recursive counterparts but
248           include stats from all the descendan    243           include stats from all the descendant cgroups.
249                                                   244 
250 Throttling/Upper limit policy files               245 Throttling/Upper limit policy files
251 -----------------------------------               246 -----------------------------------
252   blkio.throttle.read_bps_device               !! 247 - blkio.throttle.read_bps_device
253           Specifies upper limit on READ rate f !! 248         - Specifies upper limit on READ rate from the device. IO rate is
254           specified in bytes per second. Rules    249           specified in bytes per second. Rules are per device. Following is
255           the format::                            250           the format::
256                                                   251 
257             echo "<major>:<minor>  <rate_bytes    252             echo "<major>:<minor>  <rate_bytes_per_second>" > /cgrp/blkio.throttle.read_bps_device
258                                                   253 
259   blkio.throttle.write_bps_device              !! 254 - blkio.throttle.write_bps_device
260           Specifies upper limit on WRITE rate  !! 255         - Specifies upper limit on WRITE rate to the device. IO rate is
261           specified in bytes per second. Rules    256           specified in bytes per second. Rules are per device. Following is
262           the format::                            257           the format::
263                                                   258 
264             echo "<major>:<minor>  <rate_bytes    259             echo "<major>:<minor>  <rate_bytes_per_second>" > /cgrp/blkio.throttle.write_bps_device
265                                                   260 
266   blkio.throttle.read_iops_device              !! 261 - blkio.throttle.read_iops_device
267           Specifies upper limit on READ rate f !! 262         - Specifies upper limit on READ rate from the device. IO rate is
268           specified in IO per second. Rules ar    263           specified in IO per second. Rules are per device. Following is
269           the format::                            264           the format::
270                                                   265 
271            echo "<major>:<minor>  <rate_io_per    266            echo "<major>:<minor>  <rate_io_per_second>" > /cgrp/blkio.throttle.read_iops_device
272                                                   267 
273   blkio.throttle.write_iops_device             !! 268 - blkio.throttle.write_iops_device
274           Specifies upper limit on WRITE rate  !! 269         - Specifies upper limit on WRITE rate to the device. IO rate is
275           specified in io per second. Rules ar    270           specified in io per second. Rules are per device. Following is
276           the format::                            271           the format::
277                                                   272 
278             echo "<major>:<minor>  <rate_io_pe    273             echo "<major>:<minor>  <rate_io_per_second>" > /cgrp/blkio.throttle.write_iops_device
279                                                   274 
280           Note: If both BW and IOPS rules are  !! 275 Note: If both BW and IOPS rules are specified for a device, then IO is
281           subjected to both the constraints.   !! 276       subjected to both the constraints.
282                                                   277 
283   blkio.throttle.io_serviced                   !! 278 - blkio.throttle.io_serviced
284           Number of IOs (bio) issued to the di !! 279         - Number of IOs (bio) issued to the disk by the group. These
285           are further divided by the type of o    280           are further divided by the type of operation - read or write, sync
286           or async. First two fields specify t    281           or async. First two fields specify the major and minor number of the
287           device, third field specifies the op    282           device, third field specifies the operation type and the fourth field
288           specifies the number of IOs.            283           specifies the number of IOs.
289                                                   284 
290   blkio.throttle.io_service_bytes              !! 285 - blkio.throttle.io_service_bytes
291           Number of bytes transferred to/from  !! 286         - Number of bytes transferred to/from the disk by the group. These
292           are further divided by the type of o    287           are further divided by the type of operation - read or write, sync
293           or async. First two fields specify t    288           or async. First two fields specify the major and minor number of the
294           device, third field specifies the op    289           device, third field specifies the operation type and the fourth field
295           specifies the number of bytes.          290           specifies the number of bytes.
296                                                   291 
297 Common files among various policies               292 Common files among various policies
298 -----------------------------------               293 -----------------------------------
299   blkio.reset_stats                            !! 294 - blkio.reset_stats
300           Writing an int to this file will res !! 295         - Writing an int to this file will result in resetting all the stats
301           for that cgroup.                        296           for that cgroup.
                                                      

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