If you're not using XMLRPC, this will save tons of uncached requests to your site, assuming your homepage is cached properly.

xmlrpc.php

<?php

$protocol = 'https';
if ( ! isset( $_SERVER['HTTPS'] ) || $_SERVER['HTTPS'] === 'off' ) {
	$protocol = 'http';
}
$url = $protocol . "://" . $_SERVER['HTTP_HOST'];

header( 'Location: ' . $url, true, 301 );
exit;