mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-26 13:44:15 +08:00
23aa16489c
changesetfb5772cbfe("blkio-controller.txt: Remove references to CFQ") removed cgroup references to CFQ, but it kept one left. Get rid of it. Fixes:fb5772cbfe("blkio-controller.txt: Remove references to CFQ") Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
297 lines
12 KiB
ReStructuredText
297 lines
12 KiB
ReStructuredText
===================
|
|
Block IO Controller
|
|
===================
|
|
|
|
Overview
|
|
========
|
|
cgroup subsys "blkio" implements the block io controller. There seems to be
|
|
a need of various kinds of IO control policies (like proportional BW, max BW)
|
|
both at leaf nodes as well as at intermediate nodes in a storage hierarchy.
|
|
Plan is to use the same cgroup based management interface for blkio controller
|
|
and based on user options switch IO policies in the background.
|
|
|
|
One IO control policy is throttling policy which can be used to
|
|
specify upper IO rate limits on devices. This policy is implemented in
|
|
generic block layer and can be used on leaf nodes as well as higher
|
|
level logical devices like device mapper.
|
|
|
|
HOWTO
|
|
=====
|
|
Throttling/Upper Limit policy
|
|
-----------------------------
|
|
- Enable Block IO controller::
|
|
|
|
CONFIG_BLK_CGROUP=y
|
|
|
|
- Enable throttling in block layer::
|
|
|
|
CONFIG_BLK_DEV_THROTTLING=y
|
|
|
|
- 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
|
|
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
|
|
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::
|
|
|
|
# dd iflag=direct if=/mnt/common/zerofile of=/dev/null bs=4K count=1024
|
|
1024+0 records in
|
|
1024+0 records out
|
|
4194304 bytes (4.2 MB) copied, 4.0001 s, 1.0 MB/s
|
|
|
|
Limits for writes can be put using blkio.throttle.write_bps_device file.
|
|
|
|
Hierarchical Cgroups
|
|
====================
|
|
|
|
Throttling implements hierarchy support; however,
|
|
throttling's hierarchy support is enabled iff "sane_behavior" is
|
|
enabled from cgroup side, which currently is a development option and
|
|
not publicly available.
|
|
|
|
If somebody created a hierarchy like as follows::
|
|
|
|
root
|
|
/ \
|
|
test1 test2
|
|
|
|
|
test3
|
|
|
|
Throttling with "sane_behavior" will handle the
|
|
hierarchy correctly. For throttling, all limits apply
|
|
to the whole subtree while all statistics are local to the IOs
|
|
directly generated by tasks in that cgroup.
|
|
|
|
Throttling without "sane_behavior" enabled from cgroup side will
|
|
practically treat all groups at same level as if it looks like the
|
|
following::
|
|
|
|
pivot
|
|
/ / \ \
|
|
root test1 test2 test3
|
|
|
|
Various user visible config options
|
|
===================================
|
|
CONFIG_BLK_CGROUP
|
|
- Block IO controller.
|
|
|
|
CONFIG_BFQ_CGROUP_DEBUG
|
|
- 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.
|
|
|
|
Details of cgroup files
|
|
=======================
|
|
Proportional weight policy files
|
|
--------------------------------
|
|
- 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.
|
|
These rules override the default value of group weight as specified
|
|
by blkio.weight.
|
|
|
|
Following is the format::
|
|
|
|
# echo dev_maj:dev_minor weight > blkio.weight_device
|
|
|
|
Configure weight=300 on /dev/sdb (8:16) in this cgroup::
|
|
|
|
# echo 8:16 300 > blkio.weight_device
|
|
# cat blkio.weight_device
|
|
dev weight
|
|
8:16 300
|
|
|
|
Configure weight=500 on /dev/sda (8:0) in this cgroup::
|
|
|
|
# echo 8:0 500 > blkio.weight_device
|
|
# cat blkio.weight_device
|
|
dev weight
|
|
8:0 500
|
|
8:16 300
|
|
|
|
Remove specific weight for /dev/sda in this cgroup::
|
|
|
|
# echo 8:0 0 > blkio.weight_device
|
|
# cat blkio.weight_device
|
|
dev weight
|
|
8:16 300
|
|
|
|
- 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
|
|
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
|
|
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
|
|
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
|
|
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,
|
|
that is no longer true as requests may be served out of order. This
|
|
may cause the service time for a given IO to include the service time
|
|
of multiple IOs when served out of order which may result in total
|
|
io_service_time > actual time elapsed. This time is 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
|
|
io_service_time in ns.
|
|
|
|
- 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
|
|
the wait_time for its individual IOs. For devices with queue_depth > 1
|
|
this metric does not include the time spent waiting for service once
|
|
the IO is dispatched to the device but till it actually gets serviced
|
|
(there might be a time lag here due to re-ordering of requests by the
|
|
device). This is in nanoseconds to make it meaningful for flash
|
|
devices too. This time is 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 io_wait_time in ns.
|
|
|
|
- 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
|
|
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.
|
|
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.
|
|
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
|
|
cumulative total of the amount of time spent by each IO in that cgroup
|
|
waiting in the scheduler queue. This is in nanoseconds. If this is
|
|
read when the cgroup is in a waiting (for timeslice) state, the stat
|
|
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.
|
|
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
|
|
nanoseconds. If this is read when the cgroup is in an empty state,
|
|
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.
|
|
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
|
|
when the cgroup is in an idling state, the stat will only report the
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
specified in io per second. Rules are per device. Following is
|
|
the format::
|
|
|
|
echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.throttle.write_iops_device
|
|
|
|
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
|
|
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
|
|
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.
|
|
|
|
Common files among various policies
|
|
-----------------------------------
|
|
- blkio.reset_stats
|
|
- Writing an int to this file will result in resetting all the stats
|
|
for that cgroup.
|