Chapter 42. Analyzing system performance with BPF Compiler Collection As a system administrator, you can use the BPF Compiler Collection (BCC) library to create tools for analyzing the performance of your Linux operating system and gathering information, which could be difficult to obtain through other interfaces. 42.1. Installing the bcc-tools package Install the bcc-tools package, which also installs the BPF Compiler Collection (BCC) library as a dependency. Procedure Install bcc-tools . The BCC tools are installed in the /usr/share/bcc/tools/ directory. Verification Inspect the installed tools: The doc directory in the listing provides documentation for each tool. 42.2. Using selected bcc-tools for performance analyses 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 Installed bcc-tools package Root permissions Procedure Using execsnoop to examine the system processes Run the execsnoop program in one terminal: To create a short-lived process of the ls command, in another terminal, enter: The terminal running execsnoop shows the output similar to the following: 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 In one terminal, run the opensnoop program to print the output for files opened only by the process of the uname command: In another terminal, enter the command to open certain files: The terminal running opensnoop shows the output similar to the following: 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 Run the biotop program in one terminal with argument 30 to produce 30 second summary: Note When no argument provided, the output screen by default refreshes every 1 second. In another terminal, enter command to read the content from the local hard disk device and write the output to the /dev/zero file: This step generates certain I/O traffic to illustrate biotop . The terminal running biotop shows the output similar to the following: 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. Run the xfsslower program in one terminal: Note When no arguments provided, xfsslower by default displays operations slower than 10 ms. In another terminal, enter the command to create a text file in the vim editor to start interaction with the XFS file system: The terminal running xfsslower shows something similar upon saving the file from the step: 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 ) R ead W rite S ync 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.

Commands:
yum install bcc-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
/usr/share/bcc/tools/execsnoop
ls /usr/share/bcc/tools/doc/
PCOMM PID PPID RET ARGS ls 8382 8287 0 /usr/bin/ls --color=auto /usr/share/bcc/tools/doc/
/usr/share/bcc/tools/opensnoop -n uname
uname
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
/usr/share/bcc/tools/biotop 30
dd if=/dev/vda of=/dev/zero
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
/usr/share/bcc/tools/xfsslower 1
vim text
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'