docs/cgroup-v1/blkio: stop abusing itemized list

HOWTO

=====

Throttling/Upper Limit policy

-----------------------------

- Enable Block IO controller::

Enable Block IO controller::

	CONFIG_BLK_CGROUP=y

- Enable throttling in block layer::

Enable throttling in block layer::

	CONFIG_BLK_DEV_THROTTLING=y

- Mount blkio controller (see cgroups.txt, Why are cgroups needed?)::

Mount blkio controller (see cgroups.txt, Why are cgroups needed?)::

        mount -t cgroup -o blkio none /sys/fs/cgroup/blkio

- Specify a bandwidth rate on particular device for root group. The format

Specify a bandwidth rate on particular device for root group. The format

for policy is "<major>:<minor>  <bytes_per_second>"::

        echo "8:16  1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device

  Above will put a limit of 1MB/second on reads happening for root group

This will put a limit of 1MB/second on reads happening for root group

on device having major/minor number 8:16.

- Run dd to read a file and see if rate is throttled to 1MB/s or not::

Run dd to read a file and see if rate is throttled to 1MB/s or not::

        # dd iflag=direct if=/mnt/common/zerofile of=/dev/null bs=4K count=1024

        1024+0 records in

Various user visible config options

===================================

  CONFIG_BLK_CGROUP

	- Block IO controller.

	  Block IO controller.

  CONFIG_BFQ_CGROUP_DEBUG

	- Debug help. Right now some additional stats file show up in cgroup

	  Debug help. Right now some additional stats file show up in cgroup

	  if this option is enabled.

  CONFIG_BLK_DEV_THROTTLING

	- Enable block device throttling support in block layer.

	  Enable block device throttling support in block layer.

Details of cgroup files

=======================

Proportional weight policy files

--------------------------------

- blkio.weight

	- Specifies per cgroup weight. This is default weight of the group

  blkio.weight

	  Specifies per cgroup weight. This is default weight of the group

	  on all the devices until and unless overridden by per device rule.

	  (See blkio.weight_device).

	  Currently allowed range of weights is from 10 to 1000.

- blkio.weight_device

	- One can specify per cgroup per device rules using this interface.

  blkio.weight_device

	  One can specify per cgroup per device rules using this interface.

	  These rules override the default value of group weight as specified

	  by blkio.weight.

	    dev     weight

	    8:16    300

- blkio.time

	- disk time allocated to cgroup per device in milliseconds. First

  blkio.time

	  Disk time allocated to cgroup per device in milliseconds. First

	  two fields specify the major and minor number of the device and

	  third field specifies the disk time allocated to group in

	  milliseconds.

- blkio.sectors

	- number of sectors transferred to/from disk by the group. First

  blkio.sectors

	  Number of sectors transferred to/from disk by the group. First

	  two fields specify the major and minor number of the device and

	  third field specifies the number of sectors transferred by the

	  group to/from the device.

- blkio.io_service_bytes

	- Number of bytes transferred to/from the disk by the group. These

  blkio.io_service_bytes

	  Number of bytes transferred to/from the disk by the group. These

	  are further divided by the type of operation - read or write, sync

	  or async. First two fields specify the major and minor number of the

	  device, third field specifies the operation type and the fourth field

	  specifies the number of bytes.

- blkio.io_serviced

	- Number of IOs (bio) issued to the disk by the group. These

  blkio.io_serviced

	  Number of IOs (bio) issued to the disk by the group. These

	  are further divided by the type of operation - read or write, sync

	  or async. First two fields specify the major and minor number of the

	  device, third field specifies the operation type and the fourth field

	  specifies the number of IOs.

- blkio.io_service_time

	- Total amount of time between request dispatch and request completion

  blkio.io_service_time

	  Total amount of time between request dispatch and request completion

	  for the IOs done by this cgroup. This is in nanoseconds to make it

	  meaningful for flash devices too. For devices with queue depth of 1,

	  this time represents the actual service time. When queue_depth > 1,

	  specifies the operation type and the fourth field specifies the

	  io_service_time in ns.

- blkio.io_wait_time

	- Total amount of time the IOs for this cgroup spent waiting in the

  blkio.io_wait_time

	  Total amount of time the IOs for this cgroup spent waiting in the

	  scheduler queues for service. This can be greater than the total time

	  elapsed since it is cumulative io_wait_time for all IOs. It is not a

	  measure of total time the cgroup spent waiting but rather a measure of

	  minor number of the device, third field specifies the operation type

	  and the fourth field specifies the io_wait_time in ns.

- blkio.io_merged

	- Total number of bios/requests merged into requests belonging to this

  blkio.io_merged

	  Total number of bios/requests merged into requests belonging to this

	  cgroup. This is further divided by the type of operation - read or

	  write, sync or async.

- blkio.io_queued

	- Total number of requests queued up at any given instant for this

  blkio.io_queued

	  Total number of requests queued up at any given instant for this

	  cgroup. This is further divided by the type of operation - read or

	  write, sync or async.

- blkio.avg_queue_size

	- Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.

  blkio.avg_queue_size

	  Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.

	  The average queue size for this cgroup over the entire time of this

	  cgroup's existence. Queue size samples are taken each time one of the

	  queues of this cgroup gets a timeslice.

- blkio.group_wait_time

	- Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.

  blkio.group_wait_time

	  Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.

	  This is the amount of time the cgroup had to wait since it became busy

	  (i.e., went from 0 to 1 request queued) to get a timeslice for one of

	  its queues. This is different from the io_wait_time which is the

	  will only report the group_wait_time accumulated till the last time it

	  got a timeslice and will not include the current delta.

- blkio.empty_time

	- Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.

  blkio.empty_time

	  Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.

	  This is the amount of time a cgroup spends without any pending

	  requests when not being served, i.e., it does not include any time

	  spent idling for one of the queues of the cgroup. This is in

	  the stat will only report the empty_time accumulated till the last

	  time it had a pending request and will not include the current delta.

- blkio.idle_time

	- Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.

  blkio.idle_time

	  Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y.

	  This is the amount of time spent by the IO scheduler idling for a

	  given cgroup in anticipation of a better request than the existing ones

	  from other queues/cgroups. This is in nanoseconds. If this is read

	  idle_time accumulated till the last idle period and will not include

	  the current delta.

- blkio.dequeue

	- Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y. This

  blkio.dequeue

	  Debugging aid only enabled if CONFIG_BFQ_CGROUP_DEBUG=y. This

	  gives the statistics about how many a times a group was dequeued

	  from service tree of the device. First two fields specify the major

	  and minor number of the device and third field specifies the number

	  of times a group was dequeued from a particular device.

- blkio.*_recursive

	- Recursive version of various stats. These files show the

  blkio.*_recursive

	  Recursive version of various stats. These files show the

          same information as their non-recursive counterparts but

          include stats from all the descendant cgroups.

Throttling/Upper limit policy files

-----------------------------------

- blkio.throttle.read_bps_device

	- Specifies upper limit on READ rate from the device. IO rate is

  blkio.throttle.read_bps_device

	  Specifies upper limit on READ rate from the device. IO rate is

	  specified in bytes per second. Rules are per device. Following is

	  the format::

	    echo "<major>:<minor>  <rate_bytes_per_second>" > /cgrp/blkio.throttle.read_bps_device

- blkio.throttle.write_bps_device

	- Specifies upper limit on WRITE rate to the device. IO rate is

  blkio.throttle.write_bps_device

	  Specifies upper limit on WRITE rate to the device. IO rate is

	  specified in bytes per second. Rules are per device. Following is

	  the format::

	    echo "<major>:<minor>  <rate_bytes_per_second>" > /cgrp/blkio.throttle.write_bps_device

- blkio.throttle.read_iops_device

	- Specifies upper limit on READ rate from the device. IO rate is

  blkio.throttle.read_iops_device

	  Specifies upper limit on READ rate from the device. IO rate is

	  specified in IO per second. Rules are per device. Following is

	  the format::

	   echo "<major>:<minor>  <rate_io_per_second>" > /cgrp/blkio.throttle.read_iops_device

- blkio.throttle.write_iops_device

	- Specifies upper limit on WRITE rate to the device. IO rate is

  blkio.throttle.write_iops_device

	  Specifies upper limit on WRITE rate to the device. IO rate is

	  specified in io per second. Rules are per device. Following is

	  the format::

          Note: If both BW and IOPS rules are specified for a device, then IO is

          subjected to both the constraints.

- blkio.throttle.io_serviced

	- Number of IOs (bio) issued to the disk by the group. These

  blkio.throttle.io_serviced

	  Number of IOs (bio) issued to the disk by the group. These

	  are further divided by the type of operation - read or write, sync

	  or async. First two fields specify the major and minor number of the

	  device, third field specifies the operation type and the fourth field

	  specifies the number of IOs.

- blkio.throttle.io_service_bytes

	- Number of bytes transferred to/from the disk by the group. These

  blkio.throttle.io_service_bytes

	  Number of bytes transferred to/from the disk by the group. These

	  are further divided by the type of operation - read or write, sync

	  or async. First two fields specify the major and minor number of the

	  device, third field specifies the operation type and the fourth field

Common files among various policies

-----------------------------------

- blkio.reset_stats

	- Writing an int to this file will result in resetting all the stats

  blkio.reset_stats

	  Writing an int to this file will result in resetting all the stats

	  for that cgroup.