diff options
| -rw-r--r-- | Documentation/cgroups/blkio-controller.txt | 106 |
1 files changed, 103 insertions, 3 deletions
diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt index 48e0b21b005..2f5613fbe68 100644 --- a/Documentation/cgroups/blkio-controller.txt +++ b/Documentation/cgroups/blkio-controller.txt @@ -8,12 +8,17 @@ 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. -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. @@ -55,6 +60,35 @@ 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 @@ -68,8 +102,13 @@ CONFIG_CFQ_GROUP_IOSCHED - 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. @@ -210,6 +249,67 @@ Details of cgroup files 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. |