Don't use call_user_func() when you can live without it. I's 4-8 times slower!

test_call_user_func.php

<?php

class Employee {

	public static function salary()
	{
		return 0;
	}

	public function test1()
	{
		$self = get_class($this);
		return call_user_func(array($self, 'salary'));
	}

	public function test2()
	{
		return static::salary();
	}

	public function test3($true = TRUE)
	{
		if ($true)
		{
			call_user_func_array(array($this, __FUNCTION__), array( ! $true));
		}
	}

	public function test4($true = TRUE)
	{
		if ($true)
		{
			$this->test4( ! $true);
		}
	}

}


class Designer extends Employee {

	public static function salary()
	{
		return 1000;
	}

}


$designer = new Designer;


// Test 1
$start = microtime(true);

for ($i = 0; $i < 1000000; $i++)
{
	$designer->test1();
}

$end = microtime(true);

echo 'Test 1 time: ', $end - $start, '<br>';


// Test 2
$start = microtime(true);

for ($i = 0; $i < 1000000; $i++)
{
	$designer->test2();
}

$end = microtime(true);

echo 'Test 2 time: ', $end - $start, '<br>';


// Test 3
$start = microtime(true);

for ($i = 0; $i < 1000000; $i++)
{
	$designer->test3();
}

$end = microtime(true);

echo 'Test 3 time: ', $end - $start, '<br>';


// Test 4
$start = microtime(true);

for ($i = 0; $i < 1000000; $i++)
{
	$designer->test4();
}

$end = microtime(true);

echo 'Test 4 time: ', $end - $start, '<br>';