Aliyun Linux 2 optimizes the /proc/diskstats interface, which is the raw data source of the I/O latency analysis tool iostat. Aliyun Linux 2 can calculate the duration of time in read, write and special I/O (discard) on the device. In addition, Aliyun Linux 2 provides the bcc tool to track I/O latency. This topic describes the optimized /proc/diskstats interface and the bcc tool.

Interface description

The /proc/diskstats interface in Aliyun Linux 2 allows you to query the I/O information on a disk and the amount of time spent on read, write, and discard operations on a device.

Example: query the /proc/diskstats interface as a root user. 
cat /proc/diskstats
A sample response is as follows: 
254       0 vda 6328 3156 565378 2223 1610 424 25160 4366 0 1358 5332 0 0 0 0 2205 3347 0

In the response, the last three domains are new domains added in Aliyun Linux 2. The following table describes the three domains:

Domain Description
The sixteenth domain The read duration on the device. Unit: milliseconds.
The seventeenth domain The write duration on the device. Unit: milliseconds.
The eighteenth domain The discard duration on the device. Unit: milliseconds.
Note For information about other domains, see the kernel document Documentation/iostats.txt. You can obtain the kernel document from the Debuginfo package and the source code package of Aliyun Linux 2. For more information, see Use Aliyun Linux 2.

bcc

Aliyun Linux 2 provides the bcc tool that helps you track I/O latency. You must download the tool before you use it. The download command is as follows: 
yum install -y bcc-tools

You can run one of the following commands to query the description of the bcc tool.

  • Run the following command to query the description of the bcc tool. 
    /usr/share/bcc/tools/alibiolatency -h
    The description is as follows: 
    usage: alibiolatency [-h] [-d DEVICE] [-i [DIS_INTERVAL]]
                     [-t [AVG_THRESHOLD_TIME]] [-T [THRESHOLD_TIME]] [-r]

Summarize block device I/O latency

optional arguments:
  -h, --help            show this help message and exit
  -d DEVICE, --device DEVICE
                        inspect specified device
  -i [DIS_INTERVAL], --dis_interval [DIS_INTERVAL]
                        specify display interval
  -t [AVG_THRESHOLD_TIME], --avg_threshold_time [AVG_THRESHOLD_TIME]
                        display only when average request process time is
                        greater than this value
  -T [THRESHOLD_TIME], --threshold_time [THRESHOLD_TIME]
                        dump request life cycle when single request process
                        time is greater than this value
  -r, --dump_raw        dump every io request life cycle

examples:
    ./alibiolatency          # summarize block I/O latency(default display interval is 2s)
    ./alibiolatency -d sda3  # inspect specified device /dev/sda3
    ./alibiolatency -i 2     # specify display interval, 2s
    ./alibiolatency -t 10    # display only when average request process time is greater than 10ms
    ./alibiolatency -T 20    # dump request life cycle when single request process time is greater than 20ms
    ./alibiolatency -r       # dump every io request life cycle
  • Run the man command to query the description of the bcc tool. 
    man bcc-alibiolatency