Docker 资源限制之 IO

一、压测工具

通过 Linux dd 命令测试

二、IO 测试

➜  ~ docker help run | grep -E 'bps|IO'
Usage:  docker run [OPTIONS] IMAGE [COMMAND] [ARG...]
  --blkio-weight                  Block IO (relative weight), between 10 and 1000
  --blkio-weight-device=[]        Block IO weight (relative device weight)
  --device-read-bps=[]            Limit read rate (bytes per second) from a device
  --device-read-iops=[]           Limit read rate (IO per second) from a device
  --device-write-bps=[]           Limit write rate (bytes per second) to a device
  --device-write-iops=[]          Limit write rate (IO per second) to a device
➜  ~

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

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:

➜  ~ cat /sys/block/sda/queue/scheduler
noop [deadline] cfq
➜  ~ sudo sh -c "echo cfq > /sys/block/sda/queue/scheduler"
➜  ~ cat /sys/block/sda/queue/scheduler
noop deadline [cfq]

按照 Docker 官方文档的介绍测试:

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

在运行的容器上同时执行如下命令,统计测试时间:

root@0b6770ee80e0:/# time dd if=/dev/zero of=test.out bs=1M count=1024 oflag=direct
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 122.442 s, 8.8 MB/s

real    2m2.524s
user    0m0.008s
sys     0m0.492s
root@6778b6b39686:/# time dd if=/dev/zero of=test.out bs=1M count=1024 oflag=direct
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 122.493 s, 8.8 MB/s

real    2m2.574s
user    0m0.020s
sys     0m0.480s
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 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。

➜  ~ 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」:

➜  ~ docker run -it --rm --device-write-bps /dev/sda:1mb ubuntu-stress:latest /bin/bash
root@ffa51b81987c:/# dd if=/dev/zero of=test.out bs=1M count=100 oflag=direct
100+0 records in
100+0 records out
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:

➜  ~ 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」:

➜  ~ docker run -it --rm --device-write-iops /dev/sda:5 ubuntu-stress:latest /bin/bash
root@c2a2fa232594:/# dd if=/dev/zero of=test.out bs=1M count=100 oflag=direct
100+0 records in
100+0 records out
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」:

➜  ~ iostat 1
... ...
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           1.13    0.00    0.13   23.46    0.00   75.28

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda              10.00         0.00      2610.00          0       5220
... ...

读 iops 限制使用方式同写 iops 限制:

➜  ~ 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

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

–EOF–

Written by kumu on 27 March 2016