system/CodeIgniter.php
protected function startBenchmark()
	{
		$this->startTime = microtime(true);

		$this->benchmark = Services::timer();
		$this->benchmark->start('total_execution', $this->startTime);
		$this->benchmark->start('bootstrap');
	}
protected function startBenchmark()
	{
		$this->startTime = microtime(true);

		$this->benchmark = Services::timer();
		$this->benchmark->start('total_execution', $this->startTime);
		$this->benchmark->start('bootstrap');
	}
Start the Benchmark

The timer is used to display total script execution both in the
debug toolbar, and potentially on the displayed page.