This is a nifty little mu-plugin designed to assist in benchmarking plugins and snippets in WordPress. Enable the plugin from the 'settings' menu. NOTE: Not for use on Production Sites. Benchmark data WILL be shown to all viewers of the website.

gs-benchmark.php

<?php if(!defined('ABSPATH')) { die(); } // Include in all php files, to prevent direct execution
/*
Plugin Name: GS Benchmark
Plugin URI: https://gschoppe.com
Description: mu-plugin to assist in diagnosing performance issues
Version: 0.1.0
Author: Greg Schoppe
Author URI: https://gschoppe.com
*/

if( !class_exists('GSBenchmark') ) {
	class GSBenchmark {
		private $enabled    = false;
		private $start_time = 0;
		private $hook_times = array();
		private $hooks      = array();

		public static function Instance() {
			static $instance = null;
			if ($instance === null) {
				$instance = new self();
			}
			return $instance;
		}

		private function __construct() {
			$int_max = PHP_INT_MAX;
			$int_min = -1 * $int_max;

			$options = get_option('gs_benchmark');
			if( !empty( $options['enabled'] ) ) {
				$this->enabled = true;
			}
			if( !empty( $options['hooks'] ) ) {
				$this->hooks = $options['hooks'];
			}

			add_action( 'admin_menu'                     , array( $this, 'register_admin_menu' ) );
			add_action( 'admin_post_gs_benchmark_options', array( $this, 'save_options_page'   ) );

			if( $this->enabled ) {
				add_action( 'muplugins_loaded', array( $this, 'get_start_time' ), $int_min );
				if( $this->hooks && is_array( $this->hooks ) ) {
					foreach( $this->hooks as $hook ) {
						add_filter( $hook, array( $this, 'get_hook_start_time' ), $int_min );
						add_filter( $hook, array( $this, 'get_hook_end_time'   ), $int_max );
					}
				}
				add_action( 'shutdown', array( $this, 'output_end_time' ), $int_max );
			}
		}

		// Public Functions
		public function register_admin_menu() {
			add_options_page( 'GS Benchmark', 'GS Benchmark', 'manage_options', 'gs-benchmark', array( $this, 'render_options_page' ) );
		}

		public function render_options_page() {
			$form_action = admin_url('admin-post.php');
			?>
			<h1>GS Benchmark Options</h1>
			<form method="POST" action="<?php echo $form_action; ?>">
				<input type="hidden" name="action" value="gs_benchmark_options">
				<input type="hidden" name="redirect_url" value="<?php echo esc_attr( menu_page_url( 'gs-benchmark', false ) ); ?>">
				<?php wp_nonce_field( 'gs_benchmark_options_save', 'wp_nonce' ); ?>
				<label>
					<input type="checkbox" name="enable_benchmark" value="true" <?php checked( $this->enabled, true ); ?>>
					Enable Benchmarking
				</label>
				<br><br>
				<label>
					Benchmark Specific Hooks (optional, comma separated):<br>
					<textarea name="benchmark_hooks" style="display: block; width: 100%;"><?php echo esc_attr( implode( ',', $this->hooks ) ); ?></textarea>
				</label>
				<?php submit_button( "Save Options" ); ?>
			</form>
			<?php
		}

		public function save_options_page() {
			if( empty( $_POST['wp_nonce'] ) || !wp_verify_nonce( $_POST['wp_nonce'], 'gs_benchmark_options_save' ) ) {
				echo "invalid request";
				wp_die();
			}
			if( !current_user_can( 'manage_options' ) ) {
				echo "you do not have permission to modify these options";
				wp_die();
			}
			$enabled = false;
			$hooks = array();
			if( !empty( $_POST['enable_benchmark'] ) ) {
				$enabled = true;
			}
			if( !empty( $_POST['benchmark_hooks'] ) ) {
				$hooks = explode( ',', esc_attr( $_POST['benchmark_hooks'] ) );
				$hooks = array_map( 'trim', $hooks );
			}
			update_option( 'gs_benchmark', array(
				'enabled' => $enabled,
				'hooks'    => $hooks
			) );
			$url = admin_url( 'options-general.php?page=gs-benchmark' );
			if( !empty( $_POST['redirect_url'] ) ) {
				$url = $_POST['redirect_url'];
			}
			wp_redirect( $url );
			die();
		}

		public function get_start_time() {
			$this->start_time = microtime( true );
		}
		public function get_hook_start_time( $content = "" ) {
			$hook_name = current_filter();
			$this->hook_times[$hook_name] = array(
				'start' => microtime( true ),
				'end'   => 0
			);
			return $content;
		}
		public function get_hook_end_time( $content = "" ) {
			$hook_name = current_filter();
			$this->hook_times[$hook_name]['end'] = microtime( true );
			return $content;
		}
		public function output_end_time() {
			$end_time = microtime( true );
			$total    = $end_time - $this->start_time;
			$total_ms = round( $total * 1000, 3 );

			$content  = '<code class="gs-benchmark-output">';
			$content .= "PAGE GENERATED: " . date( "M-D-y H:i:s" );
			$content .= "<br>";
			$content .= "TIME TO GENERATE PAGE: " . $total_ms . " milliseconds";
			if( $this->hooks && is_array( $this->hooks ) ) {
				$content .= "<br>";
				$content .= "TIME TO PROCESS HOOKS:";
				foreach( $this->hooks as $hook ) {
					if( !isset( $this->hook_times[$hook] ) ) {
						$content .= "<br>";
						$content .= "`" . $hook . "`: NOT RUN";
						continue;
					}
					$hook_data = $this->hook_times[$hook];
					if( empty( $hook_data['start'] ) || empty( $hook_data['end'] ) ) {
						$content .= "<br>";
						$content .= "`" . $hook . "`: PROCESSING ERROR";
						continue;
					}
					$total_hook_time = $hook_data['end'] - $hook_data['start'];
					if( $total_hook_time < 0 ) {
						$content .= "<br>";
						$content .= "`" . $hook . "`: PROCESSING ERROR";
						continue;
					}
					$total_hook_time = round( $total_hook_time * 1000, 3 );
					$content .= "<br>";
					$content .= "`" . $hook . "`: " . $total_hook_time . " milliseconds";
				}
			}
			$content .= "</code>";
			$content .= "<style>";
			$content .= ".gs-benchmark-output {";
			$content .= "    position:fixed;";
			$content .= "    top: 50px;";
			$content .= "    right: 0;";
			$content .= "    background-color:#eee;";
			$content .= "    border:1px solid #ccc;";
			$content .= "    padding: 5px;";
			$content .= "    color: #f00;";
			$content .= "    z-index:99999999;";
			$content .= "    opacity:0.85;";
			$content .= "}";
			$content .= ".gs-benchmark-output:hover {";
			$content .= "    opacity:0;";
			$content .= "    pointer-events:none;";
			$content .= "}";
			$content .= "</style>";

			echo $content;
		}

	}
	GSBenchmark::Instance();
}