test.php

<?php
/**
strncmp : 0.099173069000244
substr : 0.11933302879333
substr_compare : 0.10576391220093
*/

$str = 'namespace yii\web';
$str2 = 'namespace';

$n = 100000;
$time = microtime(true);
for ($i=0; $i<$n; ++$i) {
	strncmp($str, $str2, 9);
}
echo "Total : " . (microtime(true) - $time) . "\n";

$time = microtime(true);
for ($i=0; $i<$n; ++$i) {
	substr($str, 0, 9) === $str2;
}
echo "Total : " . (microtime(true) - $time) . "\n";

$time = microtime(true);
for ($i=0; $i<$n; ++$i) {
	substr_compare($str, $str2, 0, 9);
}
echo "Total : " . (microtime(true) - $time) . "\n";