One of the main selling points of PHP 7 is greatly improved performance, with many real-world applications now running twice as fast… But where do these improvements come from? At the core of PHP 7 lies an engine rewrite with focus on improving memory usage and performance. This talk provides an overview of the most significant changes, briefly covering everything from data structure changes, over enhancements in the executor, to the new compiler implementation.

1. PHP 7
What changed internally?
Nikita Popov

2. http://hhvm.com/blog/9293/lockdown-results-and-hhvm-performance

3. Memory optimization

4. Memory optimization
• Reduce number of allocations

5. Memory optimization
• Reduce number of allocations
Memory

6. Memory optimization
• Reduce number of allocations
Memory

7. Memory optimization
• Reduce number of allocations
• PHP 5 spends 20% of CPU time in the allocator
Memory

8. Memory optimization
• Reduce number of allocations
• Reduce memory usage

9. Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Memory access has high latency

10. Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Memory access has high latency
CPU

11. Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Memory access has high latency
CPU L1D
1ns 32KB

12. Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Memory access has high latency
CPU
4ns
L2
256 KB
L1D
1ns 32KB

13. Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Memory access has high latency
CPU L312ns
a few MB
4ns
L2
256 KB
L1D
1ns 32KB

14. RAM
100ns
Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Memory access has high latency
CPU L312ns
a few MB
4ns
L2
256 KB
L1D
1ns 32KB

15. RAM
100ns
Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Memory access has high latency
• Less data => more fits into the cache
CPU L312ns
a few MB
4ns
L2
256 KB
L1D
1ns 32KB

16. Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Reduce indirection

17. Memory optimization
• Reduce number of allocations
• Reduce memory usage
• Reduce indirection
• Pointer points to pointer pointing to pointer pointing to pointer pointing to
pointer pointing to pointer pointing to what you actually want
What you
have
What you
want

18. Zvals: PHP 5
• Zval = Type + Value
value
ty
zval

19. Zvals: PHP 5
• Zval = Type + Value
value (simple):
null, bool, int, float
ty
zval

20. Zvals: PHP 5
• Zval = Type + Value
value (complex)
ty
zval
Complex data structure:
string, array, object

21. Zvals: PHP 5
• Zval = Type + Value
value (complex)
ty
zval
Complex data structure:
string, array, object
$a = [];Code:

22. Zvals: PHP 5
• Zval = Type + Value
value (complex)
ty
zval *
zval
$a:
Complex data structure:
string, array, object
$a = [];Code:

23. Zvals: PHP 5
• Zval = Type + Value
value (complex)
ty
zval *
zval
$a:
Complex data structure:
string, array, object
$a = [];
$b = $a;
Code:

24. Zvals: PHP 5
• Zval = Type + Value + Refcount
value (complex)
refcount = 1 ty
zval *
zval
$a:
Complex data structure:
string, array, object
$a = [];
$b = $a;
Code:

25. Zvals: PHP 5
• Zval = Type + Value + Refcount
value (complex)
refcount = 2 ty
zval *
zval
$a:
Complex data structure:
string, array, object
$a = [];
$b = $a;
Code:
zval *$b:

26. Zvals: PHP 7
• Zval = Type + Value
value (complex)
ty
zval *
zval
$a:
$a = [];
$b = $a;
Code:
zval *$b:
Complex data structure:
string, array, object
refcount = 2

27. Zvals: PHP 7
• Zval = Type + Value
zval *
zval
$a:
$a = [];
$b = $a;
Code:
zval *$b:
Complex data structure:
string, array, object
refcount = 2
value (complex)
type_info

28. value (complex)
type_info
value (complex)
type_info
Zvals: PHP 7
• Zval = Type + Value
$a:
Complex data structure:
string, array, object
$b:
refcount = 2
zval
zval

29. PHP 5 PHP 7
value (simple):
null, bool, int, float
refcount ty
gc_buffer
zval * value (simple): …
type_info
1 allocations
1 level of indirection
40 bytes
no allocations
no indirection
16 bytes

30. PHP 5 PHP 7
value (complex)
refcount ty
gc_root
zval *
Complex data structure:
string, array, object
value (complex)
type_info
Complex data structure:
string, array, object
refcount gc_info
2 allocations
2 levels of indirection
40 bytes
1 allocation
1 level of indirection
24 bytes

31. val (char *)
len (int)
A B C 0
zval value:
PHP 5

32. zend_string *
refcount gc_info
hash
len (size_t)
A B C 0
val (char *)
len (int)
A B C 0
zval value: zval value:
PHP 5 PHP 7

33. [0]: (empty)
[1]: (empty)
[2]: (empty)
[3]: (empty)
hash()
“xyz”
Arrays: PHP 5

34. [0]: (empty)
[1]:
[2]: (empty)
[3]: (empty)
hash()
“xyz”
data
key “xyz”
Arrays: PHP 5

35. [0]: (empty)
[1]:
[2]: (empty)
[3]:
“foo”
data
key “foo”
hash()
“xyz”
data
key “xyz”
Arrays: PHP 5

36. [0]: (empty)
[1]:
[2]: (empty)
[3]:
“foo”
data
key “foo”
hash()
“xyz”
data
key “xyz”
Arrays: PHP 5
“bar”

37. [0]: (empty)
[1]:
[2]: (empty)
[3]:
“foo”
data
key “foo”
next
data
key “bar”
next = NULL
hash()
“bar”
“xyz”
data
key “xyz”
next = NULL
Arrays: PHP 5

38. [0]: (empty)
[1]:
[2]: (empty)
[3]:
“foo”
hash()
“bar”
“xyz”
Arrays: PHP 5
head
tail
data
key “foo”
next
data
key “bar”
next = NULL
data
key “xyz”
next = NULL

39. [0]: (empty)
[1]:
[2]: (empty)
[3]:
“foo”
hash()
“bar”
“xyz”
Arrays: PHP 7
data
key “foo”
next
data
key “bar”
next = NULL
data
key “xyz”
next = NULL
head
tail

40. [0]: (empty)
[1]:
[2]: (empty)
[3]:
“foo”
hash()
“bar”
“xyz”
Arrays: PHP 7
data
key “foo”
next
data
key “bar”
next = NULL
data
key “xyz”
next = NULL

41. [0]: (empty)
[1]:
[2]: (empty)
[3]:
“foo”
hash()
“bar”
“xyz”
Arrays: PHP 7
Bucket *
uint32_t
data
key “foo”
next
data
key “bar”
next = NULL
data
key “xyz”
next = NULL

42. [0]: (empty)
[1]:
[2]: (empty)
[3]:
hash()
“bar”
“xyz”
Arrays: PHP 7
Bucket *
uint32_t
data
key “foo”
next
data
key “bar”
next = NULL
data
key “xyz”
next = NULL

43. [0]: (empty)
[1]:
[2]: (empty)
[3]:
hash()
“bar”
“xyz”
Arrays: PHP 7
Bucket *
uint32_t
TOMBSTONE
data
key “bar”
next = NULL
data
key “xyz”
next = NULL

44. PHP 5 PHP 7
Allocations: 2 + 2 per element 2 + 0 per element
Size: 72 + 112 per element 56 + 36 per element
Indirections (lookup): 4 2
Arrays: PHP 5 vs. PHP 7
(For arrays with unique values)

45. PHP 5 PHP 7
Allocations: 2 + 2 per element 2 + 0 per element
Size: 72 + 112 per element 56 + 36 per element
Indirections (lookup): 4 2
Arrays: PHP 5 vs. PHP 7
(For arrays with unique values)

46. Immutable arrays
$arrays = [];
for ($i = 0; $i < 1000000; ++$i) {
$arrays[] = [1, 2, 3, 4, 5, 6, 7, 8];
}

47. Immutable arrays
$arrays = [];
for ($i = 0; $i < 1000000; ++$i) {
$arrays[] = [1, 2, 3, 4, 5, 6, 7, 8];
}
PHP 5
Memory usage 1336 MB
Execution time (create) 0.77 s
Execution time (destroy) 1.45 s

48. Immutable arrays
$arrays = [];
for ($i = 0; $i < 1000000; ++$i) {
$arrays[] = [1, 2, 3, 4, 5, 6, 7, 8];
}
PHP 5 PHP 7
Memory usage 1336 MB 391 MB
Execution time (create) 0.77 s 0.29 s
Execution time (destroy) 1.45 s 0.05 s

49. Immutable arrays
$arrays = [];
for ($i = 0; $i < 1000000; ++$i) {
$arrays[] = [1, 2, 3, 4, 5, 6, 7, 8];
}
PHP 5 PHP 7 PHP 7 with opcache
Memory usage 1336 MB 391 MB 32 MB
Execution time (create) 0.77 s 0.29 s 0.03 s
Execution time (destroy) 1.45 s 0.05 s 0.002 s

50. Objects

51. Objects
zval
object store bucket
actual object
properties table
PHP 5
property value

52. Objects
zval
object store bucket
actual object
properties table
zval
actual object
properties table
(including values)
+
PHP 5 PHP 7
property value

53. PHP 5 PHP 7
Allocations: 2 + 1 per property 1 + 0 per property
Size: 96 + 40 per property 48 + 16 per property
Indirections (prop val): 4 1
Objects: PHP 5 vs. PHP 7
(For objects with unique properties)

54. Integers

55. Integers
64-bit integers
on
64-bit Windows

56. AST
<?php
$a = 42;
$b = 24;
echo $a + $b;

57. AST
<?php
$a = 42;
$b = 24;
echo $a + $b;
<?php T_OPEN_TAG
$a T_VARIABLE
=
42 T_LNUMBER
;
$b T_VARIABLE
=
24 T_LNUMBER
;
echo T_ECHO
$a T_VARIABLE
+
$b T_VARIABLE
;
lex

58. AST
<?php
$a = 42;
$b = 24;
echo $a + $b;
<?php T_OPEN_TAG
$a T_VARIABLE
=
42 T_LNUMBER
;
$b T_VARIABLE
=
24 T_LNUMBER
;
echo T_ECHO
$a T_VARIABLE
+
$b T_VARIABLE
;
ASSIGN $a 42
ASSIGN $b 24
ADD $a $b ~2
ECHO ~2
RETURN 1
lex
parse + compile

59. AST
<?php
$a = 42;
$b = 24;
echo $a + $b;
<?php T_OPEN_TAG
$a T_VARIABLE
=
42 T_LNUMBER
;
$b T_VARIABLE
=
24 T_LNUMBER
;
echo T_ECHO
$a T_VARIABLE
+
$b T_VARIABLE
;
ASSIGN $a 42
ASSIGN $b 24
ADD $a $b ~2
ECHO ~2
RETURN 1
lex parse
compile
stmts
assign
var 42
$a
assign
$b
echo
+
$a $b
var 24

60. AST
<?php
$a = 42;
$b = 24;
echo $a + $b;
<?php T_OPEN_TAG
$a T_VARIABLE
=
42 T_LNUMBER
;
$b T_VARIABLE
=
24 T_LNUMBER
;
echo T_ECHO
$a T_VARIABLE
+
$b T_VARIABLE
;
ASSIGN $a 42
ASSIGN $b 24
ADD $a $b ~0
ECHO ~0
RETURN 1
lex parse
compile
token_get_all()
nikic/php-ast
phpdbg -p
stmts
assign
var 42
$a
assign
$b
echo
+
$a $b
var 24

61. Virtual machine

62. Virtual machine – stack management (PHP 5)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);

63. Virtual machine – stack management (PHP 5)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
SEND_VAL 1
SEND_VAL 2
DO_FCALL foo
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0
{main}
foo()

64. Virtual machine – stack management (PHP 5)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
SEND_VAL 1
SEND_VAL 2
DO_FCALL foo
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0
{main}
foo()
…
VM stack

65. Virtual machine – stack management (PHP 5)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
SEND_VAL 1
SEND_VAL 2
DO_FCALL foo
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0
{main}
foo()
…
int(1)
int(2)
VM stack
arg[0]
arg[1]

66. Virtual machine – stack management (PHP 5)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
SEND_VAL 1
SEND_VAL 2
DO_FCALL foo
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0
{main}
foo()
…
int(1)
int(2)
execute_data
VM stack
arg[0]
arg[1]
~0
$a
$b

67. Virtual machine – stack management (PHP 5)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
SEND_VAL 1
SEND_VAL 2
DO_FCALL foo
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0
{main}
foo()
…
int(1)
int(2)
execute_data
int(1)
int(2)
VM stack
arg[0]
arg[1]
~0
$a
$b

68. Virtual machine – stack management (PHP 5)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
SEND_VAL 1
SEND_VAL 2
DO_FCALL foo
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0
{main}
foo()
…
int(1)
int(2)
int(3)
execute_data
int(1)
int(2)
VM stack
arg[0]
arg[1]
~0
$a
$b

69. Virtual machine – stack management (PHP 7)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
{main}
foo()
…
VM stack
INIT_FCALL foo
SEND_VAL 1
SEND_VAL 2
DO_FCALL
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0

70. Virtual machine – stack management (PHP 7)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
{main}
foo()
…
execute_data
VM stack
~0
$a
$b
INIT_FCALL foo
SEND_VAL 1
SEND_VAL 2
DO_FCALL
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0

71. Virtual machine – stack management (PHP 7)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
{main}
foo()
…
execute_data
int(1)
int(2)
VM stack
~0
$a
$b
INIT_FCALL foo
SEND_VAL 1
SEND_VAL 2
DO_FCALL
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0

72. Virtual machine – stack management (PHP 7)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
{main}
foo()
…
execute_data
int(1)
int(2)
VM stack
~0
$a
$b
INIT_FCALL foo
SEND_VAL 1
SEND_VAL 2
DO_FCALL
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0

73. Virtual machine – stack management (PHP 7)
function foo($a, $b) {
return $a + $b;
}
foo(1, 2);
{main}
foo()
…
execute_data
int(1)
int(2)
int(3)
VM stack
~0
$a
$b
INIT_FCALL foo
SEND_VAL 1
SEND_VAL 2
DO_FCALL
RECV $a
RECV $b
ADD $a $b ~0
RETURN ~0

74. Virtual machine – inlined internal functions
• Functions with custom opcodes:
• strlen()
• is_*()
• defined()
• call_user_func()
• call_user_func_array()

75. Virtual machine – inlined internal functions
• Functions with custom opcodes:
• strlen()
• is_*()
• defined()
• call_user_func()
• call_user_func_array()
• Only in global scope or for fully qualified calls
namespace foo;
echo strlen($str);

76. Virtual machine – inlined internal functions
• Functions with custom opcodes:
• strlen()
• is_*()
• defined()
• call_user_func()
• call_user_func_array()
• Only in global scope or for fully qualified calls
namespace foo;
echo strlen($str);
Is this strlen() or foostrlen()?

77. Virtual machine – inlined internal functions
• Functions with custom opcodes:
• strlen()
• is_*()
• defined()
• call_user_func()
• call_user_func_array()
• Only in global scope or for fully qualified calls
namespace foo;
echo strlen($str);
This is definitely strlen()!

78. Virtual machine – global registers
zend_execute_data* execute_data;
const zend_op* opline;

79. Virtual machine – global registers
register zend_execute_data* execute_data __asm__("%r14");
register const zend_op* opline __asm__("%r15");

80. Virtual machine – global registers
register zend_execute_data* execute_data __asm__("%r14");
register const zend_op* opline __asm__("%r15");
• Registers reserved in VM code

81. Virtual machine – global registers
register zend_execute_data* execute_data __asm__("%r14");
register const zend_op* opline __asm__("%r15");
• Registers reserved in VM code
• Avoid reloading from executor_globals / execute_data

82. Virtual machine – global registers
register zend_execute_data* execute_data __asm__("%r14");
register const zend_op* opline __asm__("%r15");
• Registers reserved in VM code
• Avoid reloading from executor_globals / execute_data
• Avoid save/restore during calls

83. @nikita_ppv
nikic@php.net
https://joind.in/15255