PHP 7 – What changed internally? (PHP Barcelona 2015)

PHP 7 release
Nov 12th
* if everything goes as planned

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

Memory optimization
• Reduce number of allocations

Memory optimization
Memory

Memory optimization
• PHP 5 spends 20% of CPU time in the allocator
Memory

Memory optimization
• Reduce memory usage

Memory optimization
• Memory access has high latency

Memory optimization
CPU

Memory optimization
CPU L1D
1ns 32KB

Memory optimization
CPU
4ns
L2
256 KB
L1D
1ns 32KB

Memory optimization
CPU L312ns
a few MB
4ns
L2
256 KB
L1D
1ns 32KB

RAM
100ns
Memory optimization
CPU L312ns
a few MB
4ns
L2
256 KB
L1D
1ns 32KB

RAM
100ns
Memory optimization
• Less data => more fits into the cache
CPU L312ns
a few MB
4ns
L2
256 KB
L1D
1ns 32KB

Memory optimization
• Reduce indirection

Memory optimization
• 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

Memory optimization
• Pointer points to pointer pointing to pointer pointing to pointer pointing to
pointer pointing to pointer pointing to what you actually want
• Fewer memory accesses
What you
have
What you
want

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

Zvals: PHP 5
value
ty
zval
$a = 42;Code:

Zvals: PHP 5
value = int(42)
ty
zval *
zval
$a:
$a = 42;Code:

Zvals: PHP 5
value (simple):
null, bool, int, float
ty
zval *
zval
$a:
$a = 42;Code:

Zvals: PHP 5
value (complex)
ty
zval *
zval
$a:
Complex data structure:
string, array, object
$a = [];Code:

Zvals: PHP 5
value (complex)
ty
zval *
zval
$a:
$a = [];
$b = $a;
Code:

Zvals: PHP 5
• Zval = Type + Value + Refcount
value (complex)
refcount = 1 ty
zval *
zval
$a:
$a = [];
$b = $a;
Code:

Zvals: PHP 5
• Zval = Type + Value + Refcount
value (complex)
refcount = 2 ty
zval *
zval
$a:
$a = [];
$b = $a;
Code:
zval *$b:

Zvals: PHP 7
value (complex)
ty
zval *
zval
$a:
$a = [];
$b = $a;
Code:
zval *$b:
refcount = 2

Zvals: PHP 7
zval *
zval
$a:
$a = [];
$b = $a;
Code:
zval *$b:
refcount = 2
value (complex)
type_info

value (complex)
type_info
value (complex)
type_info
Zvals: PHP 7
$a:
$b:
refcount = 2
zval
zval

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

PHP 5 PHP 7
value (complex)
refcount ty
gc_root
zval *
value (complex)
type_info
refcount gc_info
2 allocations
2 levels of indirection
40 bytes
1 allocation
1 level of indirection
24 bytes

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

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

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

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

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

[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

[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

[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

[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
Bucket *
uint32_t

PHP 5 without zval PHP 7 with zval
Allocations: 2 + 1 per element 2
Size: 72 + 80 per element 56 + 36 per element
Indirections (lookup): 4 2
Arrays: comparison

Allocations: 2 + 1 per element 2
Indirections (lookup): 4 2
PHP 5 w/ unique zvals
2 + 2 per element
72 + 112 per element
4
Arrays: comparison

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

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

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

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

handle (ID)
handlers
zval value
D V ac
object
dtor()
free_storage()
clone()
handlers
refcount
gc_root
ce
properties
properties_table
guards
[0] (stores $prop1)
[1] (stores $prop2)
[2] (stores $prop3)
zval
zval
zval
object store bucket
Zend object
Objects: PHP 5

zend_object * refcount type_info
handle
ce
handlers
properties
value
type_info
value
type_info
value
type_info
$prop1 zval
$prop2 zval
$prop3 zval
Zend object
Objects:
PHP 7

Allocations: 2 1
Indirections (prop val): 4 1
Objects: comparison

Integers
• long  zend_long
• 64-bit integers on LLP64 platforms (= Windows)

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

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

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

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

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

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

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()

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

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]

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

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

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

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

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

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

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

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

• strlen()
• is_*()
• defined()
• Only in global scope or for fully qualified calls
namespace foo;
echo strlen($str);

• strlen()
• is_*()
• defined()
namespace foo;
echo strlen($str);
Is this strlen() or foostrlen()?

• strlen()
• is_*()
• defined()
namespace foo;
echo strlen($str);
This is definitely strlen()!

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

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 reloading from executor_globals / execute_data
• Avoid save/restore during calls

Opcache
• File cache
• Alternative (or addition) to SHM

Opcache
• File cache
• Shared hosting? PHP restart / cache reset?

Opcache
• File cache
• Shared hosting? PHP restart / cache reset?
• Time for 500 sequential WP 4.1 requests
SHM 3 s
File cache 6 s
No cache 24 s

Opcache
• Huge Pages
• Code segment of PHP binary remapped into huge pages
• Reduces iTLB misses

Opcache
• Huge Pages
CPU L2L1I …

Opcache
• Huge Pages
CPU L2L1I
L1 iTLB 4K
…
L2 TLB

Opcache
• Huge Pages
CPU L2L1I
L1 iTLB 4K L1 iTLB 2M
…
L2 TLB

@nikita_ppv
nikic@php.net
https://joind.in/talk/view/15865

PHP 7 – What changed internally? (PHP Barcelona 2015)

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