Plan is to use the same cgroup based management interface for blkio controller
and based on user options switch IO policies in the background.
-In the first phase, this patchset implements proportional weight time based
-division of disk policy. It is implemented in CFQ. Hence this policy takes
-effect only on leaf nodes when CFQ is being used.
+Currently two IO control policies are implemented. First one is proportional
+weight time based division of disk policy. It is implemented in CFQ. Hence
+this policy takes effect only on leaf nodes when CFQ is being used. The second
+one 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
=====
+Proportional Weight division of bandwidth
+-----------------------------------------
You can do a very simple testing of running two dd threads in two different
cgroups. Here is what you can do.
group dispatched to the disk. We provide fairness in terms of disk time, so
ideally io.disk_time of cgroups should be in proportion to the weight.
+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
+ mount -t cgroup -o blkio none /cgroup/blkio
+
+- Specify a bandwidth rate on particular device for root group. The format
+ for policy is "<major>:<minor> <byes_per_second>".
+
+ echo "8:16 1048576" > /cgroup/blkio/blkio.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 if=/mnt/common/zerofile of=/dev/null bs=4K count=1024
+ # iflag=direct
+ 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.write_bps_device file.
+
Various user visible config options
===================================
CONFIG_BLK_CGROUP
- Enables group scheduling in CFQ. Currently only 1 level of group
creation is allowed.
+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.
and minor number of the device and third field specifies the number
of times a group was dequeued from a particular device.
+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 deivce. Following is
+ the format.
+
+ echo "<major>:<minor> <rate_bytes_per_second>" > /cgrp/blkio.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 deivce. Following is
+ the format.
+
+ echo "<major>:<minor> <rate_bytes_per_second>" > /cgrp/blkio.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 deivce. Following is
+ the format.
+
+ echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.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 deivce. Following is
+ the format.
+
+ echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.write_iops_device
+
+Note: If both BW and IOPS rules are specified for a device, then IO is
+ subjectd to both the constraints.
+
+- blkio.throttle.io_serviced
+ - Number of IOs (bio) completed to/from the disk by the group (as
+ seen by throttling policy). 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_serviced does accounting as seen by CFQ and counts are in
+ number of requests (struct request). On the other hand,
+ blkio.throttle.io_serviced counts number of IO in terms of number
+ of bios as seen by throttling policy. These bios can later be
+ merged by elevator and total number of requests completed can be
+ lesser.
+
+- 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.
+
+ These numbers should roughly be same as blkio.io_service_bytes as
+ updated by CFQ. The difference between two is that
+ blkio.io_service_bytes will not be updated if CFQ is not operating
+ on request queue.
+
+Common files among various policies
+-----------------------------------
- blkio.reset_stats
- Writing an int to this file will result in resetting all the stats
for that cgroup.
git.openpandora.org / pandora-kernel.git / blobdiff