• Docker IO资源限制
    • 一、压测工具
    • 二、IO 测试
      • 2.1 --blkio-weight、--blkio-weight-device
      • 2.2 --device-read-bps、--device-write-bps
      • 2.3 --device-read-iops、--device-write-iops
    • 三、源码解析
    • 四、拓展
    • 参考

    Docker IO资源限制

    一、压测工具

    通过 Linux dd 命令测试

    二、IO 测试

    • Runtime constraints on resources
    • 关于 IO 的限制
      • --blkio-weight=0Block IO weight (relative weight) accepts a weight value between 10 and 1000.
      • --blkio-weight-device=""Block IO weight (relative device weight, format: DEVICE_NAME:WEIGHT)针对特定设备的权重比
      • --device-read-bps=""Limit read rate from a device (format: <device-path>:<number>[<unit>]). Number is a positive integer. Unit can be one of kb, mb, or gb.按每秒读取块设备的数据量设定上限
      • --device-write-bps=""Limit write rate from a device (format: <device-path>:<number>[<unit>]). Number is a positive integer. Unit can be one of kb, mb, or gb.按每秒写入块设备的数据量设定上限
      • --device-read-iops=""Limit read rate (IO per second) from a device (format: <device-path>:<number>). Number is a positive integer.按照每秒读操作次数设定上限
      • --device-write-iops=""Limit write rate (IO per second) from a device (format: <device-path>:<number>). Number is a positive integer.按照每秒写操作次数设定上限
    1. ➜  ~ docker help run | grep -E 'bps|IO'
    2. Usage:  docker run [OPTIONS] IMAGE [COMMAND] [ARG...]
    3.   --blkio-weight                  Block IO (relative weight), between 10 and 1000
    4.   --blkio-weight-device=[]        Block IO weight (relative device weight)
    5.   --device-read-bps=[]            Limit read rate (bytes per second) from a device
    6.   --device-read-iops=[]           Limit read rate (IO per second) from a device
    7.   --device-write-bps=[]           Limit write rate (bytes per second) to a device
    8.   --device-write-iops=[]          Limit write rate (IO per second) to a device
    9. ➜  ~

    2.1 --blkio-weight、--blkio-weight-device

    • --blkio-weight

    默认，所有的容器对于 IO 操作「block IO bandwidth – blkio」都拥有相同优先级。可以通过 --blkio-weight 修改容器 blkio 权重。--blkio-weight 权重值在 10 ~ 1000 之间。

    Note: The blkio weight setting is only available for direct IO. Buffered IO is not currently supported.

    使用 blkio weight 还需要注意 IO 的调度必须为 CFQ：

    1. ➜  ~ cat /sys/block/sda/queue/scheduler
    2. noop [deadline] cfq
    3. ➜  ~ sudo sh -c "echo cfq > /sys/block/sda/queue/scheduler"
    4. ➜  ~ cat /sys/block/sda/queue/scheduler
    5. noop deadline [cfq]

    按照 Docker 官方文档的介绍测试：

    1. ➜  ~ docker run -it --rm --blkio-weight 100 ubuntu-stress:latest /bin/bash
    2. root@0b6770ee80e0:/#
    3. ➜  ~ docker run -it --rm --blkio-weight 1000 ubuntu-stress:latest /bin/bash
    4. root@6778b6b39686:/#

    在运行的容器上同时执行如下命令，统计测试时间：

    1. root@0b6770ee80e0:/# time dd if=/dev/zero of=test.out bs=1M count=1024 oflag=direct
    2. 1024+0 records in
    3. 1024+0 records out
    4. 1073741824 bytes (1.1 GB) copied, 122.442 s, 8.8 MB/s
    6. real    2m2.524s
    7. user    0m0.008s
    8. sys     0m0.492s
    9. root@6778b6b39686:/# time dd if=/dev/zero of=test.out bs=1M count=1024 oflag=direct
    10. 1024+0 records in
    11. 1024+0 records out
    12. 1073741824 bytes (1.1 GB) copied, 122.493 s, 8.8 MB/s
    14. real    2m2.574s
    15. user    0m0.020s
    16. sys     0m0.480s
    17. root@6778b6b39686:/#

    测试下来，效果不是很理想，没有获得官档的效果，类似的问题可以在相关的 issue 上找到，如 –blkio-weight doesn’t take effect in docker Docker version 1.8.1 #16173

    官方的测试说明是：

    You’ll find that the proportion of time is the same as the proportion of blkio weights of the two containers.

    • --blkio-weight-device="DEVICE_NAME:WEIGHT"

    --blkio-weight-device 可以指定某个设备的权重大小，如果同时指定 --blkio-weight 则以 --blkio-weight 为全局默认配置，针对指定设备以 --blkio-weight-device 指定设备值为主。

    1. ➜  ~ docker run -it --rm --blkio-weight-device "/dev/sda:100" ubuntu-stress:latest /bin/bash

    2.2 --device-read-bps、--device-write-bps

    限制容器的写入速度是 1mb「<device-path>:<limit>[unit]，单位可以是 kb、mb、gb 正整数」:

    1. ➜  ~ docker run -it --rm --device-write-bps /dev/sda:1mb ubuntu-stress:latest /bin/bash
    2. root@ffa51b81987c:/# dd if=/dev/zero of=test.out bs=1M count=100 oflag=direct
    3. 100+0 records in
    4. 100+0 records out
    5. 104857600 bytes (105 MB) copied, 100.064 s, 1.0 MB/s    # 可以得知写入的平均速度是 1.0 MB/s

    通过 iotop 获取测试过程中的 bps 也是 1.0 MB 为上限：

    io write bps

    读 bps 限制使用方式同写 bps 限制：

    1. ➜  ~ docker run -it --rm --device-read-bps /dev/sda:1mb ubuntu-stress:latest /bin/bash

    2.3 --device-read-iops、--device-write-iops

    限制容器 write iops 为 5「<device-path>:<limit>，必须为正整数」：

    1. ➜  ~ docker run -it --rm --device-write-iops /dev/sda:5 ubuntu-stress:latest /bin/bash
    2. root@c2a2fa232594:/# dd if=/dev/zero of=test.out bs=1M count=100 oflag=direct
    3. 100+0 records in
    4. 100+0 records out
    5. 104857600 bytes (105 MB) copied, 42.6987 s, 2.5 MB/s

    通过 iostat 监控 tps「此处即为 iops」 基本上持续在 10 左右「会有些偏差」：

    1. ➜  ~ iostat 1
    2. ... ...
    3. avg-cpu:  %user   %nice %system %iowait  %steal   %idle
    4.            1.13    0.00    0.13   23.46    0.00   75.28
    6. Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
    7. sda              10.00         0.00      2610.00          0       5220
    8. ... ...

    读 iops 限制使用方式同写 iops 限制：

    1. ➜  ~ docker run -it --rm --device-read-iops /dev/sda:5 ubuntu-stress:latest /bin/bash

    注： 在容器中通过 dd 测试读速度并没有看到很好的效果，经查没有找到磁盘读操作的好工具，所以文中没有介绍读测试。

    三、源码解析

    • github.com/opencontainers/runc/libcontainer/cgroups/fsblkio.go

    libcontainer 主要操作是对 cgroup 下相关文件根据选项写操作，具体更进一步的资源限制操作可以看 cgroup 的实现方式。

    四、拓展

    • Docker背后的内核知识——cgroups资源限制
    • cgroup 内存、IO、CPU、网络资源管理

    参考

    • http://blog.opskumu.com/docker-io-limit.html