Getting the most out of the PHP 7 engine - the example of Symfony

PHP 7.0 is already history. But do you know how to take full advantage of it? If the engine is faster on all operations in general, some of them are particularly optimized. With PHP 5, you may have taken some habits that are no longer topical to write faster code? I propose to review with you the various optimization techniques implemented in Symfony, which make the v4 the fastest ever published. This will be an opportunity to twist the puzzle around a few preconceived ideas, and give you a few more for the day when you'll try to squeeze the last few milliseconds out of this intensive loop. Benchmark in support of course.

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1. Getting the most out
   of the PHP 7 engine
   -
   the example of
   

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3. Getting the most out
   of the PHP 7 engine
   -
   the example of
   

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4. @nicolasgrekas
   

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5. live.symfony.com
   

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7. • Born in 1995 – v7 end of 2016
   • 870,000 C lines of code
   • Distributed leadership
   The PHP engine
   

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8. • Since 2011 – v4 end of 2017
   • PHP ^7.1
   • 98 packages
   • 1.5B downloads
   Symfony
   

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9. • Code infrastructure since Drupal 8
   • Now at Symfony v3.4
   • Deprecation policy and code
   • Time-based releasing process
   Symfony in Drupal
   

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10. blog.jpauli.tech
    nikic.github.io
    

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11. Synchronous and parallel
    Master
    Child 1
    Child 2
    Child n
    index.php index.php index.php
    index.php index.php index.php
    PHP’s memory manager insulates each scripts
    

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13. spl_autoload_register(
    Composer\Autoload\ClassLoader)
    Implement more in userland
    

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14. Cache
    

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15. Persistent memory pools
    Master
    Child n
    index.php index.php index.php
    Process
    memory
    Shared
    memory
    

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16. • realpath_cache_size=1M
    • clearstatcache()
    • Compiled RegExps
    • OPcache
    What does PHP cache?
    

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17. OPcache?
    

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18. Steps to execute a script
    index.php
    Lexing + parsing
    AST
    opcodes
    Compiling
    Executing
    result
    

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19. First steps are immutable
    index.php
    Lexing + parsing
    AST
    opcodes
    Compiling
    Executing
    result
    Shared
    memory*
    *append-only
    

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20. Compile time optimizations
    AST
    opcodes
    Compiling
    Shared
    memory
    • Compile-time evaluation
    'foo'."bar"
    • Dead-code elimination
    if (false) {…}
    

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21. Compile time optimizations
    AST
    opcodes
    Compiling
    Shared
    memory
    • Compile-time evaluation
    'foo'."bar"
    • Dead-code elimination
    if (false) {…}
    • Interned strings
    "foobar" len=6
    hash=Ox1234
    • Immutable arrays
    [123, ["ab" => 34]]
    len=2 len=1
    

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22. Compile time optimizations
    AST
    opcodes
    Compiling
    Shared
    memory
    • Compile-time evaluation
    'foo'."bar"
    • Dead-code elimination
    if (false) {…}
    • Interned strings
    "foobar" len=6
    hash=Ox1234
    • Immutable arrays
    [123, ["ab" => 34]]
    len=2 len=1
    

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23. • Works for constants
    'cli' === PHP_SAPI
    • Works for some native functions
    1 === count([123])
    • Needs fully-qualified identifiers
    namespace App; \count([123]);
    Compile time evaluation
    

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24. namespace App;
    is_array($a); \is_array($a);
    Compile time inlining
    https://github.com/FriendsOfPHP/PHP-CS-Fixer/issues/3048
    strlen(), is_{type}(), {type}val() casts, defined(), chr(), ord(), call_user_function(), call_user_function_array(),
    get_class(), get_called_class(), gettype(), count(), in_array(), array_slice(), func_num_args(),
    func_get_args(), function_exists(), is_callable(), extension_loaded(), constant(), dirname()
    

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25. Compile time inlining
    https://github.com/symfony/symfony/pull/25854
    

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26. Runtime-resolved identifiers are
    cached in the (local) opcode array
    Don’t « \ » all function calls
    Stick to the short list
    

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27. Let’s split the container in one file per service
    PHP 7 is slow… at compiling
    https://github.com/symfony/symfony/pull/23678
    

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28. • Loading opcodes is really fast
    • Still takes time and memory
    • « require » is also really fast
    opcodes move from
    shared memory to process’
    https://github.com/symfony/symfony/pull/23678
    

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29. Interned strings and
    immutable arrays
    stay in shared memory
    Mind opcache.interned_strings_buffer
    

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30. Leveraging shared memory
    https://blog.blackfire.io/speeding-up-autoloading-on-php-5-6-7-0-for-everyone.html
    https://blog.blackfire.io/php-7-performance-improvements-immutable-arrays.html
    

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31. • Shared memory is read-only
    $a = […]; $a[0] = 123;
    • Duplication happens on « write »
    $a = "abc";
    $b = $a;
    $b .= "ghi";
    (by the way, scalars are free, and declared properties make objects very compact)
    https://blog.blackfire.io/php-7-performance-improvements-ints-floats-free.html
    ❤ Copy-on-write
    

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32. • AbstractRecursivePass
    • ClassLoader
    • VarCloner
    $cache[$k][$v] = [$k => $v];
    Not triggering copy-on-write
    

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33. What else can be slow?
    

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34. Bypassing the autoloader
    

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35. • gc_collect_cycles()
    autotriggered past 10k objects
    • gc_mem_caches()
    PHP7 memory manager is lazy
    • Much improved in PHP 7.3
    PHP garbage collector
    

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36. • Coalesce operator
    A ?? B vs isset(A) ? A : B
    https://github.com/symfony/symfony/pull/26161
    • Ropes for encapsed strings
    "$a and $b" vs $a." and ".$b
    https://blog.blackfire.io/php-7-performance-improvements-encapsed-strings-optimization.html
    • Packed arrays (incrementing keys only)
    https://blog.blackfire.io/php-7-performance-improvements-packed-arrays.html
    • Class constants can be slow
    https://github.com/symfony/symfony/pull/25474 - https://github.com/twigphp/Twig/pull/2636
    More goodies
    

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37. • Reference mismatches are gone
    https://blog.blackfire.io/php-7-performance-improvements-references-mismatch.html
    • Copy-on-write is not triggered by (string)/(array) cast
    • Since PHP 7.2, « switch » statements use a hashmap
    • JIT is actively worked on for PHP 8 (no ETA)
    Even more goodies
    

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38. http://www.phpbenchmarks.com/en/comparator/frameworks.html
    

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39. https://rawgit.com/kocsismate/php-di-container-benchmarks/master/var/benchmark.html
    

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41. Conclusion
    • Wow PHP 7
    • Source ideas in PHP’s C
    • Use only in tight loops
    • Never stop measuring
    

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43. Join us for
    contribution sprints
    Friday, April 13, 2018
    9:00-18:00
    Room: 103
    Mentored
    Core sprint
    First time
    sprinter workshop
    General
    sprint
    #drupalsprint
    9:00-12:00
    Room: 101
    9:00-18:00
    Room: 104
    

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44. What did you think?
    Locate this session at the DrupalCon Nashville website:
    http://nashville2018.drupal.org/schedule
    Take the Survey!
    https://www.surveymonkey.com/r/nashiville
    

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