blkio: Documentation Update
o Documentation update Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>hifive-unleashed-5.1
Vivek Goyal
Jens Axboe
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8e89d13f4e
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2786c4e5e5
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@ -8,12 +8,17 @@ both at leaf nodes as well as at intermediate nodes in a storage hierarchy.
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Plan is to use the same cgroup based management interface for blkio controller
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and based on user options switch IO policies in the background.
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In the first phase, this patchset implements proportional weight time based
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division of disk policy. It is implemented in CFQ. Hence this policy takes
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effect only on leaf nodes when CFQ is being used.
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Currently two IO control policies are implemented. First one is proportional
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weight time based division of disk policy. It is implemented in CFQ. Hence
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this policy takes effect only on leaf nodes when CFQ is being used. The second
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one is throttling policy which can be used to specify upper IO rate limits
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on devices. This policy is implemented in generic block layer and can be
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used on leaf nodes as well as higher level logical devices like device mapper.
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HOWTO
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=====
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Proportional Weight division of bandwidth
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-----------------------------------------
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You can do a very simple testing of running two dd threads in two different
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cgroups. Here is what you can do.
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@ -55,6 +60,35 @@ cgroups. Here is what you can do.
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group dispatched to the disk. We provide fairness in terms of disk time, so
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ideally io.disk_time of cgroups should be in proportion to the weight.
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Throttling/Upper Limit policy
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-----------------------------
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- Enable Block IO controller
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CONFIG_BLK_CGROUP=y
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- Enable throttling in block layer
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CONFIG_BLK_DEV_THROTTLING=y
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- Mount blkio controller
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mount -t cgroup -o blkio none /cgroup/blkio
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- Specify a bandwidth rate on particular device for root group. The format
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for policy is "<major>:<minor> <byes_per_second>".
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echo "8:16 1048576" > /cgroup/blkio/blkio.read_bps_device
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Above will put a limit of 1MB/second on reads happening for root group
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on device having major/minor number 8:16.
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- Run dd to read a file and see if rate is throttled to 1MB/s or not.
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# dd if=/mnt/common/zerofile of=/dev/null bs=4K count=1024
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# iflag=direct
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1024+0 records in
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1024+0 records out
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4194304 bytes (4.2 MB) copied, 4.0001 s, 1.0 MB/s
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Limits for writes can be put using blkio.write_bps_device file.
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Various user visible config options
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===================================
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CONFIG_BLK_CGROUP
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@ -68,8 +102,13 @@ CONFIG_CFQ_GROUP_IOSCHED
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- Enables group scheduling in CFQ. Currently only 1 level of group
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creation is allowed.
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CONFIG_BLK_DEV_THROTTLING
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- Enable block device throttling support in block layer.
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Details of cgroup files
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=======================
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Proportional weight policy files
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--------------------------------
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- blkio.weight
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- Specifies per cgroup weight. This is default weight of the group
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on all the devices until and unless overridden by per device rule.
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@ -210,6 +249,67 @@ Details of cgroup files
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and minor number of the device and third field specifies the number
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of times a group was dequeued from a particular device.
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Throttling/Upper limit policy files
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-----------------------------------
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- blkio.throttle.read_bps_device
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- Specifies upper limit on READ rate from the device. IO rate is
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specified in bytes per second. Rules are per deivce. Following is
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the format.
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echo "<major>:<minor> <rate_bytes_per_second>" > /cgrp/blkio.read_bps_device
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- blkio.throttle.write_bps_device
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- Specifies upper limit on WRITE rate to the device. IO rate is
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specified in bytes per second. Rules are per deivce. Following is
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the format.
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echo "<major>:<minor> <rate_bytes_per_second>" > /cgrp/blkio.write_bps_device
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- blkio.throttle.read_iops_device
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- Specifies upper limit on READ rate from the device. IO rate is
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specified in IO per second. Rules are per deivce. Following is
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the format.
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echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.read_iops_device
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- blkio.throttle.write_iops_device
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- Specifies upper limit on WRITE rate to the device. IO rate is
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specified in io per second. Rules are per deivce. Following is
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the format.
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echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.write_iops_device
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Note: If both BW and IOPS rules are specified for a device, then IO is
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subjectd to both the constraints.
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- blkio.throttle.io_serviced
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- Number of IOs (bio) completed to/from the disk by the group (as
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seen by throttling policy). These are further divided by the type
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of operation - read or write, sync or async. First two fields specify
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the major and minor number of the device, third field specifies the
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operation type and the fourth field specifies the number of IOs.
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blkio.io_serviced does accounting as seen by CFQ and counts are in
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number of requests (struct request). On the other hand,
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blkio.throttle.io_serviced counts number of IO in terms of number
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of bios as seen by throttling policy. These bios can later be
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merged by elevator and total number of requests completed can be
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lesser.
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- blkio.throttle.io_service_bytes
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- Number of bytes transferred to/from the disk by the group. These
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are further divided by the type of operation - read or write, sync
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or async. First two fields specify the major and minor number of the
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device, third field specifies the operation type and the fourth field
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specifies the number of bytes.
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These numbers should roughly be same as blkio.io_service_bytes as
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updated by CFQ. The difference between two is that
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blkio.io_service_bytes will not be updated if CFQ is not operating
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on request queue.
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Common files among various policies
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-----------------------------------
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- blkio.reset_stats
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- Writing an int to this file will result in resetting all the stats
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for that cgroup.
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