![ABOUT THE LINUX SYSTEM
TIPS: Explanation
CAT
PROCESS
GREP
PROCESS
The ring buffer provided by the kernel
/DEV/PTS/0
PROCESS
pipe:[412981]
①Read file descriptor 0(entity：/dev/pts/0)
read(0, “hoge¥n”, 65536)
②Write file descriptor1(entiry：pipe:[412981])
write(1, “hoge¥n”, 5)
③Read file descriptor0(entity：pipe:[412981])
read(0, “hoge¥n”, 32768)
about write call
about read call
about ring buffer
about file descriptor](https://image.slidesharecdn.com/about-linux-english-180514021957/85/About-linux-english-21-320.jpg)
About linux-english
- 1. Shota Ito About the linux system
- 2. ABOUT THE LINUX SYSTEM Promise ▸ Today I can not reach the kernel itself… ▸ Talking about today is very difficult :( And I do not know too many things. It is normal not to understand. ▸ An old programmer may understand from the experience of writing C. ▸ The theme is too large so it is about the summary. ▸ If there are people who are interested please listen individually :)
- 3. ABOUT THE LINUX SYSTEM What is Linux ?
- 4. Linux is a name which broadly denotes a family of free and open- source software operating system distributions built around the Linux kernel. Wikipedia
- 5. Kernel Device Device driver Thread scheduler File system Network stack Virtual memory System call User Layer Kernel Layer System library Database Application
- 6. ABOUT THE LINUX SYSTEM What is system library
- 7. Kernel Device Device driver Thread scheduler File system Network stack Virtual memory System call User Layer Kernel Layer System library Database Application
- 8. ABOUT THE LINUX SYSTEM What is system library ? ▸ Famous library is glibc(GNU C Library) ▸ Forexample, php and java is using glibc ▸ and more openldap-devel.x86_64, openssl- devel.x86_64, zlib-devel.x86_64…etc
- 9. ABOUT THE LINUX SYSTEM Example: php code (https://github.com/php/php-src)
- 10. ABOUT THE LINUX SYSTEM mysqli.c
- 11. ABOUT THE LINUX SYSTEM zend_alloc.h
- 12. ABOUT THE LINUX SYSTEM zend_alloc.h
- 13. ABOUT THE LINUX SYSTEM What is system call
- 14. Kernel Device Device driver Thread scheduler File system Network stack Virtual memory System call User Layer Kernel Layer System library Database Application
- 15. ABOUT THE LINUX SYSTEM What is system call ? ▸ System call is the interface between the application and the kernel. ▸ Why need system call? ▸ The authority is too large for direct hardware control. ▸ ex)get the memory! open the socket because i want to correspond! fork the process!…etc
- 16. ABOUT THE LINUX SYSTEM What system calls are there ? ▸ read/write: Using a file descriptor, read the byte and place it in buffer. ▸ malloc：Call it when get memory ▸ clone(fork)：Call it when fork the process ▸ getsockname：Call it when get socket name ▸ accept,accept4 : Call it when accept connection
- 17. ABOUT THE LINUX SYSTEM Watch system call for apache httpd ▸ Get all call # strace $(for pid in `pgrep httpd`;do echo -n "-p $pid ";done) ▸ Get getsockname,accept,accept4 # strace $(for pid in `pgrep httpd`;do echo -n "-p $pid ";done) -e trace=getsockname,accept,accept4 ▸ for using grep strace $(for pid in `pgrep httpd`;do echo -n "-p $pid ";done) 2>&1 | grep ‘192.168.120.129' ▸ What happens if I disconnect the connection with iptables ?
- 18. ABOUT THE LINUX SYSTEM TIPS: How pipe works ▸ What do you often use “|” ?
- 19. ABOUT THE LINUX SYSTEM TIPS: Check the pipe works ▸ ex：$ cat hoge.txt | grep ito ▸ Chase ”cat | grep ito” at the system call level ▸ strace -p `pgrep cat` ▸ strace -p `pgrep grep` ▸ lsof -p `pgrep cat` ▸ lsof -p `pgrep grep`
- 20. ABOUT THE LINUX SYSTEM
- 21. ABOUT THE LINUX SYSTEM TIPS: Explanation CAT PROCESS GREP PROCESS The ring buffer provided by the kernel /DEV/PTS/0 PROCESS pipe:[412981] ①Read file descriptor 0(entity：/dev/pts/0) read(0, “hoge¥n”, 65536) ②Write file descriptor1(entiry：pipe:[412981]) write(1, “hoge¥n”, 5) ③Read file descriptor0(entity：pipe:[412981]) read(0, “hoge¥n”, 32768) about write call about read call about ring buffer about file descriptor
- 22. ABOUT THE LINUX SYSTEM Talk of the kernel so finish : )
- 23. ABOUT THE LINUX SYSTEM How does this knowledge help?
- 24. ABOUT THE LINUX SYSTEM Pre-release performance troubleshooting (true story… WEB APP ▸ I do not really understand something, but it's late! Investigate! DBLB HOW MUCH IS THE RESPONSE RETURNED? WHAT'S THE ERROR? NO PROBLEM APPLICATION RESPONSE & ERROR SEEMS TO BE PROBLEMATIC? RESPONSE IS NOT ON !! IS NOT DB HEAVY ? NO PROBLEM
- 25. ABOUT THE LINUX SYSTEM APP ▸ Taking the system call graph of the application, it took about 40% to read the encryption processing library. ▸ Tell application developers to solve them by reviewing the encryption algorithm. WHILE ACQUIRING THE SYSTEM CALL, CHECK THE CONTENTS WITH LOAD. 参考：CPU Flame Graphs Pre-release performance troubleshooting (true story…
- 26. ABOUT THE LINUX SYSTEM Understand what is going on 参考：Linux Performance Tools
- 27. ABOUT THE LINUX SYSTEM Performance tuning ▸ Since it is communicating with socket, it is better to increase the file descriptor ▸ Will you leave the cache management of the database to OS or application? ▸ High CPU utilization! ▸ User land? Kernel land? Context switch?
- 28. ABOUT THE LINUX SYSTEM Reference
- 29. ABOUT THE LINUX SYSTEM Reference ▸ Linux Networking Architecture ▸ gdb Debugging Full Example (Tutorial): ncurses
- 30. ABOUT THE LINUX SYSTEM Q&A ▸ Which layer captures packets captured from tcpdump? ▸ Get data from the device driver. 引用：Linux Network Internals