Taming memory: performance-tuning a (Crystal) application [SoundCloud HQ edition]

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Taming memory: Performance-tuning a (Crystal) application Denis Defreyne / SoundCloud HQ / November 24, 2015 1

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The contents of this talk aren’t particularly revolutionary. 2 DISCLAIMER

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C 5

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Gosu (Ruby) 6 ✂

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LÖVE (Lua) 7 ✂

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Rust 10

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Crystal 11 ✂

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I don’t know much about game development. 12 DISCLAIMER

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memory, the game memory, the computer thingie 18

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Allocating objects 19

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donkey = Donkey.new(3, "grey") 20

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donkey = Donkey.allocate donkey.initialize(3, "grey") 21

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donkey = malloc(6).cast(Donkey) donkey.initialize(3, "grey") 22

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What is memory? 23

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25 0 1 2 3 4 5 6 7 8 9 A B C D E F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 …

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26 0 1 2 3 4 5 6 7 E F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 …

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27 0 1 2 3 4 5 6 7 3 G R E Y Ø E F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 …

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Freeing memory 28

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donkey = malloc(6).cast(Donkey) donkey.initialize(3, "grey") free(donkey) 29

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Garbage collection 30 ✨

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Calling functions 31

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10 LET S = 0 15 MAT INPUT V 20 LET N = NUM 30 IF N = 0 THEN 99 40 FOR I = 1 TO N 45 LET S = S + V(I) 50 NEXT I 60 PRINT S/N 70 GO TO 10 99 END 33

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10 LET S = 0 15 MAT INPUT V 20 LET N = NUM 30 IF N = 0 THEN 99 40 FOR I = 1 TO N 45 LET S = S + V(I) 50 NEXT I 60 PRINT S/N 70 GO TO 10 99 END 34

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Structured programming [makes] extensive use of subroutines […] 35

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return 36

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9074: eb 4a jmp 90c0 <_mysql_init_character_set+0x124> 9076: 8b 43 f8 mov -0x8(%rbx),%eax 9079: 83 f8 01 cmp $0x1,%eax 907c: 74 04 je 9082 <_mysql_init_character_set+0xe6> 907e: 85 c0 test %eax,%eax 9080: 75 06 jne 9088 <_mysql_init_character_set+0xec> 9082: 4c 8b 7b f0 mov -0x10(%rbx),%r15 9086: eb 38 jmp 90c0 <_mysql_init_character_set+0x124> 9088: 48 8b 4b f0 mov -0x10(%rbx),%rcx 908c: 48 8d 35 15 a3 03 00 lea 0x3a315(%rip),%rsi # 433a8 <_zcfree+0x1fd6> 9093: bf 51 04 00 00 mov $0x451,%edi 9098: 31 d2 xor %edx,%edx 909a: 31 c0 xor %eax,%eax 909c: e8 72 76 02 00 callq 30713 <_my_printf_error> 90a1: 48 8d 35 56 a3 03 00 lea 0x3a356(%rip),%rsi # 433fe <_zcfree+0x202c> 90a8: 4c 8d 3d 61 b9 03 00 lea 0x3b961(%rip),%r15 # 44a10 <_zcfree+0x363e> 90af: bf 51 04 00 00 mov $0x451,%edi 90b4: 31 d2 xor %edx,%edx 90b6: 31 c0 xor %eax,%eax 90b8: 4c 89 f9 mov %r15,%rcx 37

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0000000000030713 <_my_printf_error>: 30713: 55 push %rbp 30714: 48 89 e5 mov %rsp,%rbp 30717: 41 57 push %r15 30719: 41 56 push %r14 3071b: 41 54 push %r12 3071d: 53 push %rbx 3071e: 48 81 ec d0 02 00 00 sub $0x2d0,%rsp … 30932: 4c 3b 75 e8 cmp -0x18(%rbp),%r14 30936: 75 0c jne 30944 <_my_printf_warning+0xda> 30938: 48 81 c4 d0 02 00 00 add $0x2d0,%rsp 3093f: 5b pop %rbx 30940: 41 5e pop %r14 30942: 5d pop %rbp 30943: c3 retq 38

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39 main

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39 my_printf_error main call

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39 my_printf_error main STACK call (4 byte elements)

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39 return address my_printf_error main STACK call (4 byte elements)

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39 return address my_printf_error main STACK call my_vsnprintf_ex call (4 byte elements)

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39 return address my_printf_error main STACK call my_vsnprintf_ex return address call (4 byte elements)

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39 return address my_printf_error main STACK call my_vsnprintf_ex call ret (4 byte elements)

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39 my_printf_error main STACK call ret my_vsnprintf_ex call ret (4 byte elements)

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Passing arguments 40

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41 …

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41 param 1 …

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41 param 1 param 2 …

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41 param 1 param 2 return address …

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41 param 1 param 2 …

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41 …

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42 …

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42 param param return address …

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42 param param return address … param return address

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42 param param return address … param return address return address

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42 param param return address … param return address

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42 param param return address …

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42 …

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Storing local variables 43

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44 …

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44 param param return address …

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44 param param return address … local variable local variable

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44 param param return address …

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44 …

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Collecting garbage 46

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47 param 1 param 2 return address local variable 1 local variable 2 local variable 3 local variable local variable

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47 param 1 param 2 return address local variable 1 local variable 2 local variable 3 local variable local variable

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47 ? ? local variable local variable

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48 ? ? local variable local variable

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49 ? ? Mark phase local variable local variable

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50 Sweep phase local variable local variable

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Mark and sweep: the simplest GC technique 51

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79% of time spent in the garbage collector‽ 53

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‽ interrobang — U+203D 54 ( )

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Stop this GC madness! 55

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Avoiding garbage collection:  three techniques 56

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Avoiding garbage collection  through explicit reuse 57

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1_000_000.times do point = Point.new(random(width), random(height)) draw(point) end 58

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point = Point.new 1_000_000.times do point.x = random(width) point.y = random(height) draw(point) end 59

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- only works for a single instance - mutating state can lead to bugs 60

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Avoiding garbage collection  through memory pooling 61

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pool = Pool(Entity).new(1000)  62

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pool = Pool(Entity).new(1000)  entity = pool.acquire  62

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pool = Pool(Entity).new(1000)  entity = pool.acquire  pool.release(entity) 62

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+ can reuse multiple objects - memory management is more manual 63

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Avoiding garbage collection  through stack allocation 64

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65 …

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65 param param return address …

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65 param param return address … local variable local variable

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65 param param return address …

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65 …

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class Point getter :x, :y def initialize(@x, @y) end end 66

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struct Point getter :x, :y def initialize(@x, @y) end end 67

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1_000_000.times do point = Point.new(random(width), random(height)) draw(point) end 68

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+ no explicit memory management - only usable for local variables 69

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Don’t destroy the CPU cache! 70

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71 HD

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71 HD RAM

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71 HD RAM Cache

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71 HD RAM Cache ~ 1 000 000 ns

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71 HD RAM Cache ~ 1 000 000 ns ~ 500 ns

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71 HD RAM Cache ~ 1 000 000 ns ~ 1-10 ns ~ 500 ns

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If data is available in the cache, we have a cache hit. If it’s not available in the cache, we have a cache miss. 74

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To avoid cache misses, keep similar data together in memory. 75

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76 position velocity rotation armor shield

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77 position velocity (for movement) rotation armor shield

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77 position velocity 14 used bytes / 32 total bytes = 44% efficiency (for movement) rotation armor shield

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Store similar data in contiguous arrays. 80

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positions = Pool(Position).new(1000) velocities = Pool(Velocity).new(1000) 81

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Demo 82

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Demo: Stack allocation 83

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84 r

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84 r

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#total (2 × r) 2 #inside π × r 2 85 ≈

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#total (2 × r) 2 #inside π × r 2 85 ≈

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#total 4 #inside π 86 ≈

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4 × #inside #total 87 π ≈

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(use the source, luke) 88

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Demo: Cache grinding 89

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(use the source, luke) 90

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92 slack @denis / mail denis@soundcloud.com Denis Defreyne Ask me about anything but potatoes.

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Extra slides 93

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94 lldb, gdb debugger Instruments (Mac OS X) performance analyser and visualiser dtrace dynamic tracing framework