Potential performance issue with DOM in JIT

[YuanchengJiang]

Description

The following code:

<?php
$GLOBALS['_start_time'] = microtime(true);
function test_document_import() {
    $xml = <<<XML
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<div xmlns="http://www.w3.org/1999/xhtml">
    <p>Test-Text</p>
</div>
</feed>
XML;
    $dom = new DOMDocument();
    $dom->loadXML($xml);
    $dom2 = new DOMDocument();
    $importedNode = $dom2->importNode($dom->documentElement, true);
    $dom2->appendChild($importedNode);
    $dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);$dom2->appendChild($importedNode);
}
test_document_import();
$execution_time = microtime(true) - $GLOBALS['_start_time'];
echo "Execution time: {$execution_time} seconds\n";
?>

Just curious )

I found the execution of DOM operations in JIT 1215 is relatively much slower (more than 100x times) than normal executions. Wondering if it is expected or not? If you lower down the optimization bit like 1211 or trigger bit 1205, the performance becomes reasonable.

To reproduce:

-d "zend_extension=/php-src/modules/opcache.so" -d "opcache.enable=1" -d "opcache.enable_cli=1" -d "opcache.jit=1215"

PHP Version

nightly

Operating System

ubuntu 22.04

[nielsdos]

I can't reproduce this.
Note that you might've gotten confused. Depending on some settings you can get the time formatted as scientific notation vs not at a certain cut-off point.
e.g. for me I sometimes get the execution time output 0.0001(...) vs 7.0(...)E-5; but those are roughly the same execution time.

[YuanchengJiang]

1215: Execution time: 0.018915891647339 seconds (try to execute it for many times, the first time the performance might look reasonable)
1205: Execution time: 0.00011706352233887 seconds
1211: Execution time: 0.00090694427490234 seconds

It has linear heavy performance delay if having many appendChild, and the diff can over 1000x times.

[nielsdos]

Are you testing this on a debug build or a release build? Also can you share your php.ini?

[YuanchengJiang]

I can reproduce it in the latest commit via default ./configure with GCC or clang, either with debug symbol or not. I use command line with a temp ini to execute the script:

~/WorkSpace/php-src$ ./sapi/cli/php -n -c '/tmp/tmp-php.ini' -d "zend_extension=/php-src/modules/opcache.so" -d "opcache.enable=1" -d "opcache.enable_cli=1" -d "opcache.jit=1215" /tmp/test.php 
Execution time: 0.03252100944519 seconds
~/WorkSpace/php-src$ ./sapi/cli/php -n -c '/tmp/tmp-php.ini' -d "zend_extension=/php-src/modules/opcache.so" -d "opcache.enable=1" -d "opcache.enable_cli=1" -d "opcache.jit=1211" /tmp/test.php 
Execution time: 0.00075602531433105 seconds