PHP 7 performances from PHP 5

PHP 7 performances
From PHP 5 in Symfony context

Hello everybody
 Julien PAULI
 SensioLabs Blackfire team
 Programming with PHP since early 2000s
 Now : Unix system programmer (C)
 PHP Internals programmer/reviewer
 PHP 5.5 & 5.6 Release Manager
 @julienpauli
 Tech blog at jpauli.github.io
 jpauli@php.net

What we'll cover together
 Profiling a simple SF2 app
 Under PHP 5
 Under PHP 7
 Compare profiles using Blackfire graph comparison
 Analyze numbers
 Dive into PHP 7 performances
 Structures optimizations
 New variable model (zval)
 New HashTable model
 String management with zend_string
 Other ideas...

Profiles
 Done on my laptop (not on prod env)
 LP64
 Done on app_dev.php (debug mode)
 Do not take numbers for real
 But relative measures
 Performed with Blackfire
 On PHP-5.6 latest
 On PHP-7.0.0RC8

Blackfire
 General profiler
 Not only PHP, but works best for PHP
 Free version exists
 Collects many metrics
 memory, CPU, IO, Network trafic, SQL ...
 Graphs useful info, trashes useless info
 Immediately spot your perf problems
 Nice graph comparison view

Blackfire collector
 Collector is a PHP extension
 ~ 5000 C lines
 Available for 5.3, 5.4, 5.5 and 5.6
 In beta for PHP 7, but soon to be released
 In beta for Windows platforms, but soon to be
released
 Collector impact is NULL if not triggered
 Collector works in prod environment
 It is highly optimized for performances
 It is finely optimized for each PHP version

Profiles
 Done on my laptop
 Done with app_dev.php
 Do not take numbers for real
 But relative measures

Which PHP ?
 PHP 7 is slower than PHP 5 ...
 When no OPCode cache is used !
 This is a 15% perf difference
 (Remember numbers target this SF2-based small
app)
PHP 5
PHP 7

PHP 7 changes
 PHP 7 now uses an AST based compiler
 The PHP 7 compiler is SLOWER than PHP 5's
 But much more well designed
 Creating and compiling an AST is slow
 The AST is hookable with PHP extensions
 The AST is hookable in userland using nikic/php-ast
 The compiler is more complex, it tries to optimize runtime
 ... But as you use an OPCode cache
 This is not a problem to you
 PHP 7 compiler generates better runtime OPCodes
 Your runtime will be better compared to PHP 5

Profiling with OPCache
PHP 7
PHP 5

Comparing view, with OPCache
 PHP 7 runs faster on this app by a factor of 23%
 PHP 7 CPU usage is 22% less than PHP 5
 PHP 7 memory footprint is 38% less than PHP 5
 ~ 3.85Mb less in our case

Comparing view, with OPCache
 Some components benefit more than others of PHP
7 performance optimizations

Optimizing CPU time
 Latency Numbers Every Programmer Should Know
 http://lwn.net/Articles/250967/
 http://www.eecs.berkeley.edu/~rcs/research/interactive_l
atency.html
2016 numbers (may vary with chip)
---------------------------------------------------
L1 cache reference 1 ns
Branch mispredict 3 ns
L2 cache reference 4 ns 4x L1 cache
L3 cache reference 12 ns 3X L2 cache, 12x L1 cache
Main memory reference 100 ns 25x L2 cache, 100x L1 cache
SSD random read 16,000 ns
HDD random read(seek) 200,000,000 ns

Optimizing CPU cache efficiency
 If we can reduce payload size, the CPU will use its
caches more often
 CPU caches prefetch data on a "line" basis
 Improve data locality to improve cache efficiency
 https://software.intel.com/en-us/articles/optimize-data-
structures-and-memory-access-patterns-to-improve-
data-locality
 That means in C
 Reduce number of pointer indirections
 Stick data together (struct hacks, struct merges)
 Use smaller data sizes

caches more often
PHP 5.6 (debug)
456,483483 task-clock # 0,974 CPUs utilized
1 405 context-switches # 0,003 M/sec
7 CPU-migrations # 0,000 M/sec
8 633 page-faults # 0,019 M/sec
1 163 771 607 cycles # 2,549 GHz
<not supported> stalled-cycles-frontend
<not supported> stalled-cycles-backend
1 247 617 395 instructions # 1,07 insns per cycle
181 700 375 branches # 398,044 M/sec
5 257 940 branch-misses # 2,89% of all branches
9 085 235 cache-references # 20,787 M/sec
1 108 044 cache-misses # 12,196 % of all cache refs
0,468451813 seconds time elapsed

caches more often
PHP 7.0.0RC8 (debug)
306,006739 task-clock # 0,916 CPUs utilized
1 446 context-switches # 0,005 M/sec
2 CPU-migrations # 0,000 M/sec
4 330 page-faults # 0,014 M/sec
787 684 146 cycles # 2,574 GHz
<not supported> stalled-cycles-frontend
<not supported> stalled-cycles-backend
817 673 456 instructions # 1,04 insns per cycle
121 452 445 branches # 396,895 M/sec
3 356 650 branch-misses # 2,76% of all branches
5 741 559 cache-references # 18,464 M/sec
873 581 cache-misses # 15,215 % of all cache refs

PHP 7 cache efficiency
PHP 7.0.0RC8 (debug)
306,006739 task-clock
1 446 context-switches
4 330 page-faults
787 684 146 cycles
817 673 456 instructions
121 452 445 branches
3 356 650 branch-misses
5 741 559 cache-references
873 581 cache-misses
PHP 5.6 (debug)
456,483483 task-clock
1 405 context-switches
8 633 page-faults
1 163 771 607 cycles
1 247 617 395 instructions
181 700 375 branches
5 257 940 branch-misses
9 085 235 cache-references
1 108 044 cache-misses

PHP 7 optimizations
 Every variable in PHP is coded on a zval struct
 This struct has been reorganized in PHP 7
 Narrowed / shrinked
 separated

PHP 5 variables
value
refcount is_ref
type
gc_info
dval
str_val* str_len
hashtable*
object*
lval
ast*
zval
zval_value
...
...
HashTable
32 bytes
$a
8 bytes
zval *
XX bytes
 40 bytes + complex value size
 2 indirections

PHP 7 variables
value
type
internal_int
dval
zend_string*
object*
lval
...
zval
zval_value
...
...
HashTable
16 bytes
$a
zval
XX bytes
 16 bytes + complex value size
 1 indirection
hashtable*
gc_infos
refcount
infosflags
gc_infos

PHP 5 vs PHP 7 variable design
 zval container no longer stores GC infos
 No more need to heap allocate a zval *
 GC infos stored into each complex types
 each complex type may now be shared
 In PHP 5, we had to share the zval containing them
 PHP 7 variables are more CPU cache efficient

Hashtables (arrays)
 In PHP, HashTables are used to represent the PHP
array type
 But HashTables are also used internally
 Everywhere
 HashTables optimization in PHP 7 are well felt as
they are heavilly used internally

HashTables in PHP 5
 Each element needs
 4 pointer indirections
 72 bytes for a bucket + 32 bytes for a zval
zval
zval *
HashTable
$a
zval *
HashTable*
bucket *
zval
64 bytes
72 bytesbucket

HashTables in PHP 7
 Each element needs
 2 pointer indirections
 32 bytes for a bucket
zval
bucket
HashTable
$a
zval
HashTable*
zval
56 bytes
32 bytes
bucket*

PHP 7 Hash
 Memory layout is as contiguous as possible
hash"foo" 1234 | (-table_size) -3
nIndex

PHP 7 Hash
 Memory layout is as contiguous as possible
hash"foo" 1234 | (-table_size) -3
buckets*
arData
-1-2-3
2 X XX
-4 1 2
nIndex
nIndex idx
idx
hash
key
zval
bucket

PHP 7 HashTables memory layout
 $a['foo'] = 42;
arData
-6-7
arData[0]
arData[1]
42 bucket

String management
 In PHP 5, strings don't have their own structure
 String management is hard
 Leads to many strings duplication
 Many more memory access
 In PHP 7, strings share the zend_string structure
 They are refcounted
 hashes are precomputed, often at compile time
 struct hack is used to compact memory

Strings in PHP
char * str
...
zval
gc_infos
int len
refcount is_ref zend_string *
...
zval
...
hash
gc_infos
char str[1]size_t len
...
zend_string
PHP 5 PHP 7

Strings in PHP 5
 $a = "foo";
3 0X00007FFFF7F8C708
foo0

Strings in PHP 7
 $a = "foo";
foo0
C struct hack
3
memory border

Comparing VM times for array operations
PHP 7
PHP 5

Other VM operation comparisons
 Casts
PHP 7
PHP 5

 Concatenations
PHP 7
PHP 5

 @ usage (error suppression)
PHP 7
PHP 5

PHP 7 is released :-)
get it now <3

PHP 7 performances from PHP 5

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