"If we were able to take a microscope and observe how our programs work on the lowest level, we would be surprised and shocked. Close to the wire, programs behave very differently from what we expect. In this session we will go through code examples that show the counter-intuitive behavior of Java on the microscopic scale. We will take a detailed look at how the underlying technology works that causes the surprising behavior and how we can measure our programs on the lowest level. Topics covered will be the cache hierarchy, false sharing, pipelining, branch prediction, and out-of-order execution. After this talk you will have a good understanding of how modern CPUs work and how this can affect the performance of your programs."

1. The Quantum Physics
of Java
Michael Heinrichs
Canoo Engineering AG

2. for (int i = 0; i < n; i++) {
a[i] *= 3;
}
for (int i = 0; i < n; i+=16) {
a[i] *= 3;
} 26,1 ms
25,8 ms

3. Michael Heinrichs
http://blog.netopyr.com
@net0pyr
canoo
delivering end-user happiness[ ]

4. for (int i = 0; i < n; i++) {
a[i] *= 3;
}
for (int i = 0; i < n; i+=16) {
a[i] *= 3;
} 26,1 ms
25,8 ms

5. CPU
Main Memory

6. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
CPU

7. CPU
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1

8. CPU
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
3

9. CPU
3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
3

10. CPU
3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1

11. CPU
3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
3

12. CPU
3 3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
3

13. 1980 1985 1990 1995 2000 2005 2010
1
10
100
1000
10000
100000
CPU
Memory
Year
Performance

14. Main Memory
CPU

15. Main Memory
Cache
CPU

16. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
CPU

17. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1
CPU

18. CPU
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1
1

19. CPU
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1
3

20. CPU
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
3 1 1 1 1 1
3

21. CPU
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
3 1 1 1 1 1
1

22. CPU
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
3 1 1 1 1 1
3

23. CPU
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
3 3 1 1 1 1
3

24. for (int i = 0; i < n; i++) {
a[i % a.length] *= 3;
}

25. 1 KB 2 KB 4 KB 8 KB 16 KB 32 KB 64 KB 128 KB 256 KB 512 KB 1 MB 2 MB 4 MB 8 MB 16 MB 32 MB 64 MB 128 MB 256 MB
0
1
2
3
4
5
6
7

26. CPU
Main Memory
Cache

27. Main Memory
L1 Cache
L2 Cache
L3 Cache
CPU

28. 1 KB 2 KB 4 KB 8 KB 16 KB 32 KB 64 KB 128 KB 256 KB 512 KB 1 MB 2 MB 4 MB 8 MB 16 MB 32 MB 64 MB 128 MB 256 MB
0
1
2
3
4
5
6
7

29. Not quite pints
By radioedit (CC BY-SA 2.0)

30. Main Memory
L1 Cache
L2 Cache
L3 Cache
< 1 ns, 32 KB
7 ns, 256 KB
25 ns, 8 MB
100 ns, 16 GB
CPU

31. for (int i = 0; i < n; i++) {
a[i % a.length] *= 3;
}
for (int i = 0; i < n; i++) {
a[rnd()] *= 3;
}

32. 1 KB
2 KB
4 KB
8 KB
16 KB
32 KB
64 KB
128 KB
256 KB
512 KB
1 MB
2 MB
4 MB
8 MB
16 MB
32 MB
64 MB
128 MB
256 MB
0
1
2
3
4
5
6
7

33. 1 KB
2 KB
4 KB
8 KB
16 KB
32 KB
64 KB
128 KB
256 KB
512 KB
1 MB
2 MB
4 MB
8 MB
16 MB
32 MB
64 MB
128 MB
256 MB
0
5
10
15
20
25

34. 1 KB
2 KB
4 KB
8 KB
16 KB
32 KB
64 KB
128 KB
256 KB
512 KB
1 MB
2 MB
4 MB
8 MB
16 MB
32 MB
64 MB
128 MB
256 MB
0
5
10
15
20
25

35. perf

36. perf stat application

37. perf stat -p 1234 sleep 5

40. Main Memory
L1 Cache
L2 Cache
L3 Cache
CPU

41. 1 1 1 1 1 11 1 1 1 11 1 1 1 1
CPU

42. 1 1 1 1 1 11 1 1 1 11 1 1 1 1
1 1 1 1
CPU

43. CPU
1 1 1 1 1 11 1 1 1 11 1 1 1 1
1 1 1 1
1

44. CPU
1 1 1 1 1 11 1 1 1 11 1 1 1 1
1 1 1 1
1
1 1 1 1

45. 1 KB
2 KB
4 KB
8 KB
16 KB
32 KB
64 KB
128 KB
256 KB
512 KB
1 MB
2 MB
4 MB
8 MB
16 MB
32 MB
64 MB
128 MB
256 MB
0
5
10
15
20
25

46. int a;
Thread 1: a++;
Thread 2: return a;
2,1 ops/ns
1,2 ops/ns

47. Main Memory
L2 Cache
L3 Cache
L1 Cache L1 Cache
Core 1 Core 2

48. L1 Cache L1 Cachea
Core 1 Core 2

49. L1 Cache L1 Cachea a
?
Core 1 Core 2

50. Modified Exclusive
Shared Invalid

51. Modified Exclusive
Shared Invalid

52. Modified Exclusive
Shared Invalid

53. Modified Exclusive
Shared Invalid

54. Modified Exclusive
Shared Invalid

55. Modified Exclusive
Shared Invalid

56. Modified Exclusive
Shared Invalid

57. L1 Cache L1 Cachea a
Core 1 Core 2

58. int a;
int b;
Thread 1: a++;
Thread 2: return b;
2,1 ops/ns
1,2 ops/ns

59. L1 Cache L1 Cachea b
Core 1 Core 2

60. L1 Cache L1 Cachea ab b
Core 1 Core 2

61. Given: sorted int[16]
Linear or Binary Search?
21,8 ns 28,2 ns

63. A
B
C
D
E
CPU

64. Fetch
A
A
B
C
D
E

65. Fetch Decode
A
A
B
C
D
E

66. Fetch Decode Execute
A
A
B
C
D
E

67. Fetch Decode Execute Write-
back
A
A
B
C
D
E

68. Fetch Decode Execute Write-
back
A
A
B
C
D
E

69. Fetch Decode Execute Write-
back
B
A
B
C
D
E A

70. Fetch Decode Execute Write-
back
C
A
B
C
D
E B A

71. Fetch Decode Execute Write-
back
D
A
B
C
D
E C B A

72. Fetch Decode Execute Write-
back
E
A
B
C
D
E D C B

73. Fetch Decode Execute Write-
back
A
B
C
D
E

74. Fetch Decode Execute Write-
back
A
B
C
D
E A

75. Fetch Decode Execute Write-
back
A
B
C
D
E A?

76. Fetch Decode Execute Write-
back
A
B
C
D
E AB

77. Fetch Decode Execute Write-
back
A
B
C
D
E C B A

78. Fetch Decode Execute Write-
back
A
B
C
D
E C B A

79. Fetch Decode Execute Write-
back
A
B
C
D
E C B A

80. Fetch Decode Execute Write-
back
A
B
C
D
E AE

81. Binary Search
while (low <= high)
…
if (midVal < needle)
…
else if (midVal > needle)
…
else
…

82. Linear Search
for element : haystack
if element == needle
…
else if (element > needle)
…

83. int a;
int b;
a *= 3;
a *= 5;
a *= 3;
b *= 5;
2,3 ns
2,1 ns

85. Fetch Decode Execute Write-
back

86. Fetch Decode Execute Write-
back
Execute
Execute

87. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch

88. Fetch Decode Write-
back
Fetch
Fetch
A
B
C
Execute
Execute
Execute

89. Fetch Decode Write-
back
Fetch
Fetch
A
B
C
A
B
C
Execute
Execute
Execute

90. Fetch Decode Write-
back
Fetch
Fetch
A
B C
A
B
C
Execute
Execute
Execute

91. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch
A
B
C
A
B
C

92. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch
A
B
C
A
B
C

93. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch
A
B
C
A
B
C

94. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch
A
B
C AB
C

95. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch
A
B
C B
C

96. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch
A
B
C
C

97. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch
A
B
C
C

98. Fetch Decode Execute Write-
back
Execute
Execute
Fetch
Fetch
A
B
C

99. a *= 3 a *= 5
a *= 3
b *= 5
int a;
int b;
a *= 3;
a *= 5;
a *= 3;
b *= 5;

100. Know thy CPU
(because sometimes it matters)

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To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/4.0/ or send a letter
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