Systems programming is for everyone

Transcript

1. SYSTEMS PROGRAMMING IS FOR EVERYONE by Julia Evans Stripe twitter: @b0rk blog: jvns.ca Tweet questions to @b0rk
2. ὁὁ bugs ὁὁ
3. perl | go | c++ | fortran php | python | java | smalltalk INTERCAL | BASIC | erlang
4. MOSTLY LINUX ὂ
5. YOUR PROGRAM = BLACK BOX
6. DEBUGGING: look at the source code add print statements know the programming language
7. DEBUGGING: look at the source code add print statements know the programming language ★★★ be a wizard★★★
9. THIS TALK Wizard school (or, an operating systems primer) Chapter 1: The Case of the Mystery Config File Chapter 2: The Case of the French Website Chapter 3: The Case of the Slow Program
10. WIZARD SCHOOL -OR- WHY YOU SHOULD ❤ YOUR OPERATING SYSTEM
11. WHAT IS AN OPERATING SYSTEM FOR?
12. When I go to http://google.com, kernel code runs for: Typing in the address Handling every network packet Writing history files to disk Allocating memory Communicating with the graphics card
13. HOW TO CALL OPERATING SYSTEM CODE
14. ★★★ SYSTEM CALLS!!! ★★★
15. SYSTEM CALLS: AN OS'S INTERFACE open a file! (o p e n ) start a program! (e x e c v e ) change a file's permissions! (c h m o d )
16. WHAT WE'VE LEARNED Your OS does tons of stuff Programs tell it what to do using system calls
17. USING SYSTEMS KNOWLEDGE TO DEBUG
18. CHAPTER 1: THE CASE OF THE MYSTERY CONFIG FILE
19. Does bash use . b a s h _ p r o f i l e or . b a s h r c ??!??
20. STRACE = ⚡ WIZARDRY ⚡
21. STRACE = TRACING SYSTEM CALLS
22. HOW TO STRACE $ s t r a c e g o o g l e - c h r o m e e x e c v e ( " / u s r / b i n / g o o g l e - c h r o m e " , [ " g o o g l e - c h r o m e " ] , [ / * 5 1 v a r s * / ] b r k ( 0 ) = 0 x 1 2 4 f 0 0 0 a c c e s s ( " / e t c / l d . s o . n o h w c a p " , F _ O K ) = - 1 E N O E N T ( N o s u c h f i l e o
24. OPEN strace ­e open bash
25. BASHRC WINS!
26. OTHER AWESOME SYSTEM CALLS w r i t e for log files e x e c v e for starting programs r e c v f r o m for receiving data
27. STRACE ZINE
28. OPENSNOOP LINUX ὂ & OS X ἴ ! https://github.com/iovisor/bcc
29. opensnoop(8) NAME opensnoop ­ Trace open() syscalls. Uses Linux eBPF/bcc. ... AUTHOR Brendan Gregg
30. CHAPTER 2: THE CASE OF THE POLISH WEBSITE
33. ???
34. NETWORK SPYING TO THE RESCUE
35. TCPDUMP sudo tcpdump port 5000 ­i any ­o polish­website.pcap
36. WIRESHARK wireshark polish­website.pcap
37. Accept­Language: en­US,en;q=0.5\r\n
44. WIRESHARK: ASSIGNER OF BLAME
45. why tcpdump is fast: BPF (berkeley packet filter) src ip 192.168.0.1 or dst ip 192.168.0.1
46. NETWORK SPYING TOOLS ngrep tcpdump wireshark mitmproxy
47. CHAPTER 3: THE CASE OF THE SLOW PROGRAM
48. 3 SLOW PROGRAMS 1. CPU time 2. too many writes 3. waiting for a slow server
49. MYSTERY PROGRAM #1
50. $ time python mystery_1.py 0.09user 0.01system 0:02.11elapsed 5%CPU
51. WHAT IS IT WAITING FOR?
52. LET'S LOOK INTO THE KERNEL'S SOUL
53. /PROC/P I D /STACK $ p g r e p - f m y s t e r y _ 1 3 1 7 2 8 $ s u d o c a t / p r o c / 3 1 7 2 8 / s t a c k [ < f f f f f f f f 8 1 7 0 2 4 6 7 > ] s k _ w a i t _ d a t a + 0 x 1 0 7 / 0 x 1 2 0 [ < f f f f f f f f 8 1 7 6 7 1 1 2 > ] t c p _ r e c v m s g + 0 x 2 e 2 / 0 x b 8 0 [ < f f f f f f f f 8 1 7 9 4 d 6 e > ] i n e t _ r e c v m s g + 0 x 7 e / 0 x b 0 [ < f f f f f f f f 8 1 6 f d b 6 b > ] s o c k _ r e c v m s g + 0 x 3 b / 0 x 5 0 [ < f f f f f f f f 8 1 6 f d d c 1 > ] S Y S C _ r e c v f r o m + 0 x e 1 / 0 x 1 6 0 [ < f f f f f f f f 8 1 6 f f 1 c e > ] S y S _ r e c v f r o m + 0 x e / 0 x 1 0 [ < f f f f f f f f 8 1 8 2 4 4 f 2 > ] e n t r y _ S Y S C A L L _ 6 4 _ f a s t p a t h + 0 x 1 6 / 0 x 7 1 [ < f f f f f f f f f f f f f f f f > ] 0 x f f f f f f f f f f f f f f f
54. WE WIN! IT WAS THE NETWORK!
55. OUR SERVER @app.route('/') def slow(): time.sleep(2) return "Hi!" app.run()
56. MYSTERY PROGRAM #2 $ time python mystery_2.py 2.74user 0.00system 2.74 seconds 99%CPU
57. USE A PYTHON PROFILER
58. total = 0 for i in xrange(14000000): total += i
59. MYSTERY PROGRAM #3
60. (REALLY A MYSTERY)
61. $ time python mystery_3.py 0.03user 4.11system 4.40 seconds elapsed 94%CPU
62. DEMO DEMO
63. 29,81% [kernel] _aesni_enc1 1,88% [kernel] ecryptfs_write_begin ▒ 1,51% [kernel] raw_spin_lock
64. MYSTERY SOLVED filename = '/home/bork/fake.txt'
65. ❤ dstat ❤
66. ❤ perf top ❤
67. WORKS GREAT WITH THE JVM & NODE
68. rust_mutex system_call_fastpath ttwu_.. en.. enq.. enqu.. futex_wait main::.. [unknown] _raw_.. [unknown] futex_wake do_futex __ticket_spin_lock __schedule __lll_lock_wait wake_futex acti.. schedule sys_futex futex_wait_que.. dea.. __lll_unlock_wake wake_up_state _raw_spin_lock __tic.. __ticket_spin_lock de.. try_to_wake_up se.. _raw_spin_lock ttwu_.. system_call_fastpath deq.. d.. sys_futex futex_wait_setup do_futex
69. YOUR PROGRAM = BLACK BOX
70. THERE ARE A LOT OF AWESOME TOOLS
71. LEARN YOUR OPERATING SYSTEM (or your browser.)
72. Recurse Center
73. PROGRAMMING PROGRAMMING EXPERIMENTS EXPERIMENTS
74. RULES OF RULES OF PROGRAMMING PROGRAMMING EXPERIMENTS EXPERIMENTS it doesn't have to work 1. you don't have to finish it 2. you have to learn something 3.
75. EXPERIMENT 1: WRITE AN EXPERIMENT 1: WRITE AN OPERATING SYSTEM OPERATING SYSTEM remember it doesn't have to work
76. WHAT I LEARNED WHAT I LEARNED having more than once process is hard filesystems are hard operating systems are SO COMPLICATED
77. EXPERIMENT 2: EXPERIMENT 2: DATABASE SURGERY DATABASE SURGERY
78. HOW DOES SQLITE HOW DOES SQLITE WORK? WORK?
79. FUN.SQLITE FUN.SQLITE id | word 1 | greedy 2 | greediness 3 | greener
80. $ hexdump fun.sqlite |.............{.n| |.a.R.D.4.%......| |................| |...y.n._.N.>.,.$| |................| |..............F.| |..EAcevedo.E...D| |Accra's.D...CAcc| |ra.C..#BAccentur| |e's.B...AAccentu| |re.A..!@Acapulco| |'s.@...?Acapulco|
81. A DATABASE IS A A DATABASE IS A TREE TREE
82. static MemPage *btreePageFromDbPage(DbPage *pDbPage, Pgno pgno, BtSha // actual code printf("Read a btree page, page number %d\n", pgno); // added by me // actual code }
83. sqlite> select * from fun where id = 1; Read a btree page, page number 1 Read a btree page, page number 5 Read a btree page, page number 828 Read a btree page, page number 10 Read a btree page, page number 2 Read a btree page, page number 76 Read a btree page, page number 6 1|A's
84. sqlite> select * from fun where id = 20; Read a btree page, page number 1 Read a btree page, page number 5 Read a btree page, page number 828 Read a btree page, page number 10 Read a btree page, page number 2 Read a btree page, page number 76 Read a btree page, page number 6 20|Aaliyah
85. sqlite> select * from fun where id = 80000; Read a btree page, page number 1 Read a btree page, page number 5 Read a btree page, page number 1198 Read a btree page, page number 992 Read a btree page, page number 2 Read a btree page, page number 1813 Read a btree page, page number 449 80000|scarfs
86. WHAT I LEARNED WHAT I LEARNED databases tables are trees databases are made of pages i can read some of the SQLite source code!
87. EXPERIMENT 3: EXPERIMENT 3: WRITE A TCP STACK WRITE A TCP STACK
88. EXPERIMENT 3: EXPERIMENT 3: WRITE A TCP STACK WRITE A TCP STACK IN PYTHON IN PYTHON
90. ip_header = IP(dst=dest_ip, src=src_ip) syn = TCP(dport=80, sport=59333, ack=0, flags="S") # Send the SYN packet to Google response = srp(ip_header + syn)
91. WHAT I LEARNED WHAT I LEARNED how TCP packets are put together! you can write a 10% working TCP from scratch in 2 weeks python can't keep up
92. EXPERIMENT 4: EXPERIMENT 4: CONCURRENCY CONCURRENCY
93. int counter; void *AddThings(void *threadid) { for (int i = 0; i < 10000; i++) counter += 1; pthread_exit(NULL); }
94. WRONG ANSWER WRONG ANSWER
95. MUTEX MUTEX pthread_mutex_lock(&mutex); counter += 1;
96. "ATOM" "ATOM" __sync_add_and_fetch(&counter, 1);
97. WHAT I LEARNED WHAT I LEARNED atoms are faster than mutexes
98. I BLOG MY EXPERIMENTS I BLOG MY EXPERIMENTS
99. "can you discuss the pros and cons of using a lock-free approach for implementing a thread-safe hashmap?"
100. DO ENOUGH DO ENOUGH EXPERIMENTS EXPERIMENTS END UP WITH ACTUAL END UP WITH ACTUAL KNOWLEDGE KNOWLEDGE
101. THANKS! Julia Evans twitter: @b0rk learn more by reading my blog: http://jvns.ca Come ask me questions & get a zine!