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Chapter 44. Analyzing system performance with BPF Compiler Collection

The BPF Compiler Collection (BCC) analyzes system performance by combining the capabilities of Berkeley Packet Filter (BPF). With BPF, you can safely run the custom programs within the kernel to access system events and data for performance monitoring, tracing, and debugging. BCC simplifies the development and deployment of BPF programs with tools and libraries for users to extract important insights from their systems.

44.1. Installing the bcc-tools package
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Install the bcc-tools package, which also installs the BPF Compiler Collection (BCC) library as a dependency.

Procedure

  • Install bcc-tools. 

    # yum install bcc-tools

    The BCC tools are installed in the /usr/share/bcc/tools/ directory.

Verification

  • Inspect the installed tools: 

    # ls -l /usr/share/bcc/tools/
...
-rwxr-xr-x. 1 root root  4198 Dec 14 17:53 dcsnoop
-rwxr-xr-x. 1 root root  3931 Dec 14 17:53 dcstat
-rwxr-xr-x. 1 root root 20040 Dec 14 17:53 deadlock_detector
-rw-r--r--. 1 root root  7105 Dec 14 17:53 deadlock_detector.c
drwxr-xr-x. 3 root root  8192 Mar 11 10:28 doc
-rwxr-xr-x. 1 root root  7588 Dec 14 17:53 execsnoop
-rwxr-xr-x. 1 root root  6373 Dec 14 17:53 ext4dist
-rwxr-xr-x. 1 root root 10401 Dec 14 17:53 ext4slower
...

    The doc directory in the listing provides documentation for each tool.

Use certain pre-created programs from the BPF Compiler Collection (BCC) library to efficiently and securely analyze the system performance on the per-event basis. The set of pre-created programs in the BCC library can serve as examples for creation of additional programs.

Prerequisites

Procedure

Using execsnoop to examine the system processes
  1. Run the execsnoop program in one terminal: 
# /usr/share/bcc/tools/execsnoop

  1. To create a short-lived process of the ls command, in another terminal, enter: 

    $ ls /usr/share/bcc/tools/doc/

  2. The terminal running execsnoop shows the output similar to the following: 

    PCOMM	PID    PPID   RET ARGS
ls   	8382   8287     0 /usr/bin/ls --color=auto /usr/share/bcc/tools/doc/
...

    The execsnoop program prints a line of output for each new process that consume system resources. It even detects processes of programs that run very shortly, such as ls, and most monitoring tools would not register them.

    The execsnoop output displays the following fields:

PCOMM
The parent process name. (ls)
PID
The process ID. (8382)
PPID
The parent process ID. (8287)
RET
The return value of the exec() system call (0), which loads program code into new processes.
ARGS
The location of the started program with arguments.

To see more details, examples, and options for execsnoop, see /usr/share/bcc/tools/doc/execsnoop_example.txt file.

For more information about exec(), see exec(3) manual pages.

Using opensnoop to track what files a command opens
  1. In one terminal, run the opensnoop program to print the output for files opened only by the process of the uname command: 
# /usr/share/bcc/tools/opensnoop -n uname

  1. In another terminal, enter the command to open certain files: 

    $ uname

  2. The terminal running opensnoop shows the output similar to the following: 

    PID    COMM 	FD ERR PATH
8596   uname 	3  0   /etc/ld.so.cache
8596   uname 	3  0   /lib64/libc.so.6
8596   uname 	3  0   /usr/lib/locale/locale-archive
...

    The opensnoop program watches the open() system call across the whole system, and prints a line of output for each file that uname tried to open along the way.

    The opensnoop output displays the following fields:

    PID
    The process ID. (8596)
    COMM
    The process name. (uname)
    FD
    The file descriptor - a value that open() returns to refer to the open file. (3)
    ERR
    Any errors.
    PATH
    The location of files that open() tried to open.

    If a command tries to read a non-existent file, then the FD column returns -1 and the ERR column prints a value corresponding to the relevant error. As a result, opensnoop can help you identify an application that does not behave properly.

To see more details, examples, and options for opensnoop, see /usr/share/bcc/tools/doc/opensnoop_example.txt file.

For more information about open(), see open(2) manual pages.

Use the biotop to monitor the top processes performing I/O operations on the disk
  1. Run the biotop program in one terminal with argument 30 to produce 30 second summary: 
# /usr/share/bcc/tools/biotop 30
Note

When no argument provided, the output screen by default refreshes every 1 second.

  1. In another terminal, enter command to read the content from the local hard disk device and write the output to the /dev/zero file: 

    # dd if=/dev/vda of=/dev/zero

    This step generates certain I/O traffic to illustrate biotop.

  2. The terminal running biotop shows the output similar to the following: 

    PID    COMM             D MAJ MIN DISK       I/O  Kbytes     AVGms
9568   dd               R 252 0   vda      16294 14440636.0  3.69
48     kswapd0          W 252 0   vda       1763 120696.0    1.65
7571   gnome-shell      R 252 0   vda        834 83612.0     0.33
1891   gnome-shell      R 252 0   vda       1379 19792.0     0.15
7515   Xorg             R 252 0   vda        280  9940.0     0.28
7579   llvmpipe-1       R 252 0   vda        228  6928.0     0.19
9515   gnome-control-c  R 252 0   vda         62  6444.0     0.43
8112   gnome-terminal-  R 252 0   vda         67  2572.0     1.54
7807   gnome-software   R 252 0   vda         31  2336.0     0.73
9578   awk              R 252 0   vda         17  2228.0     0.66
7578   llvmpipe-0       R 252 0   vda        156  2204.0     0.07
9581   pgrep            R 252 0   vda         58  1748.0     0.42
7531   InputThread      R 252 0   vda         30  1200.0     0.48
7504   gdbus            R 252 0   vda          3  1164.0     0.30
1983   llvmpipe-1       R 252 0   vda         39   724.0     0.08
1982   llvmpipe-0       R 252 0   vda         36   652.0     0.06
...

    The biotop output displays the following fields:

PID
The process ID. (9568)
COMM
The process name. (dd)
DISK
The disk performing the read operations. (vda)
I/O
The number of read operations performed. (16294)
Kbytes
The amount of Kbytes reached by the read operations. (14,440,636)
AVGms
The average I/O time of read operations. (3.69)

For more details, examples, and options for biotop, see the /usr/share/bcc/tools/doc/biotop_example.txt file.

For more information about dd, see dd(1) manual pages.

Using xfsslower to expose unexpectedly slow file system operations

The xfsslower measures the time spent by XFS file system in performing read, write, open or sync (fsync) operations. The 1 argument ensures that the program shows only the operations that are slower than 1 ms.

  1. Run the xfsslower program in one terminal: 

    # /usr/share/bcc/tools/xfsslower 1
    Note

    When no arguments provided, xfsslower by default displays operations slower than 10 ms.

  2. In another terminal, enter the command to create a text file in the vim editor to start interaction with the XFS file system: 

    $ vim text

  3. The terminal running xfsslower shows something similar upon saving the file from the previous step: 

    TIME     COMM           PID    T BYTES   OFF_KB   LAT(ms) FILENAME
13:07:14 b'bash'        4754   R 256     0           7.11 b'vim'
13:07:14 b'vim'         4754   R 832     0           4.03 b'libgpm.so.2.1.0'
13:07:14 b'vim'         4754   R 32      20          1.04 b'libgpm.so.2.1.0'
13:07:14 b'vim'         4754   R 1982    0           2.30 b'vimrc'
13:07:14 b'vim'         4754   R 1393    0           2.52 b'getscriptPlugin.vim'
13:07:45 b'vim'         4754   S 0       0           6.71 b'text'
13:07:45 b'pool'        2588   R 16      0           5.58 b'text'
...

    Each line represents an operation in the file system, which took more time than a certain threshold. xfsslower detects possible file system problems, which can take form of unexpectedly slow operations.

    The xfsslower output displays the following fields:

    COMM
    The process name. (b’bash')
    T

    The operation type. (R)

    • Read
    • Write
    • Sync
    OFF_KB
    The file offset in KB. (0)
    FILENAME
    The file that is read, written, or synced.

To see more details, examples, and options for xfsslower, see /usr/share/bcc/tools/doc/xfsslower_example.txt file.

For more information about fsync, see fsync(2) manual pages.

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