Alibaba Cloud Linux 2 optimizes the /proc/diskstats raw data source interface of the I/O latency analysis tool iostat. Alibaba Cloud Linux 2 can calculate the amount of time taken by read, write, and special I/O (discard) operations on devices. In addition, Alibaba Cloud 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 Alibaba Cloud Linux 2 allows you to query the I/O information on a disk and the amount of time taken by read, write, and discard operations on a device.

Example: Query the /proc/diskstats interface by using the root account. 
cat /proc/diskstats
Example output: 
254       0 vda 6328 3156 565378 2223 1610 424 25160 4366 0 1358 5332 0 0 0 0 2205 3347 0

In the output, the last three domains are new domains added in Alibaba Cloud Linux 2. The following table describes the three domains.

Domain Description
The sixteenth domain The amount of time taken by read operations on the device. Unit: ms.
The seventeenth domain The amount of time taken by write operations on the device. Unit: ms.
The eighteenth domain The amount of time taken by discard operations on the device. Unit: ms.
Note For information about other domains, visit the kernel document Documentation/iostats.txt. You can obtain the kernel document from the Debuginfo package and source code package of Alibaba Cloud Linux 2. For more information, see Use Alibaba Cloud Linux 2.

bcc

Alibaba Cloud Linux 2 provides the bcc tool to track I/O latency. You must download the tool before you can use it. Run the following command to download the tool: 
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
    Sample description: 
    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