Autoloader: High Performance Overhead Despite OPCache

[Mukeshoad]

Impacted plugin

Jetpack

Quick summary

Jetpack Autoloader is consistently among the slowest parts of page load. Even with OPCache enabled, profiling shows hundreds of calls to PHP_Autoloader::load_class, adding significant latency.

Steps to reproduce

Jetpack Autoloader is consistently among the slowest parts of page load. Even with OPCache enabled, profiling shows hundreds of calls to PHP_Autoloader::load_class, adding significant latency.

Steps to Reproduce

Activate Jetpack + WooCommerce.

Profile any shop or checkout page.

Observe autoloader call count (~1000+) and total time (>300ms).

Environment

WooCommerce 10.x

PHP 8.2–8.4

OPCache enabled (512MB)

Litespeed server

Impact
Front-end performance degraded, especially on high-traffic stores.

Site owner impact

More than 60% of the total website/platform users

Severity

Major/Critical

What other impact(s) does this issue have?

No response

If a workaround is available, please outline it here.

No response

Platform (Simple and/or Atomic)

No response

[mreishus]

What method are you using to determine the time spent in the load_class function?

[mreishus]

@Mukeshoad Here's a small profiler we can use to look at two parts of the JP Autoloader:

• find_class_file - locating the php file
• require - including the file

It doesn't change behavior and is safe to remove.

How to use it:
Temporarily disable other profiling methods (xdebug, code profiler pro, spx...). They can affect timings.
Install the file - Copy the file below, jp-autoloader-profiler.php into wp-content/mu-plugins/
Enable logging in wp-config.php:

define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );

Optional settings to increase logging detail, or to completely takeover the autoloader if we don't see enough entries

// Turn this on to completely remove Jetpack's autoloader and replace it
// define( 'JP_AUTOLOADER_PROBE_TAKEOVER', true );

// Turn this on to see per-class and per file timings:
// define( 'JP_AUTOLOADER_PROBE_DETAIL', 'true' );

Load a few slow pages
Examine the log - wp-content/debug.log

For example, I see ~1100 calls into it with about 3ms taken in total, 2.3ms of it in require

[23-Sep-2025 23:49:02 UTC] JP probe coverage - seen: 1129, found: 609, required: 609
[23-Sep-2025 23:49:02 UTC] AC Debug Summary for: /wp-admin/admin-ajax.php
Label                                      |    Count |   Total (ms) |   Avg (ms) |     Median |        Min |        Max
----------------------------------------------------------------------------------------------------------------------------
JP find_class_file                         |     1104 |         0.73 |       0.00 |       0.00 |       0.00 |       0.00
JP require                                 |      550 |         2.30 |       0.00 |       0.00 |       0.00 |       0.02
----------------------------------------------------------------------------------------------------------------------------

• If the coverage line shows required: 0, or lower than expected, please add define('JP_AUTOLOADER_PROBE_TAKEOVER', true); and re-run.
• If one of the parts is slow, use define( 'JP_AUTOLOADER_PROBE_DETAIL', 'true' ); and we should get one timing per class or file that's over 1 ms to run.

Clean up - When done, remove wp-content/mu-plugins/jp-autoloader-profiler.php

This will let us see whether the time is in file lookup vs file include, and whether it's one or two outliers or spread across many files.

jp-autoloader-profiler.php

<?php
/**
 * Plugin Name: JP Autoloader Profiler (order-aware)
 * Description: Measures Jetpack autoloader time in find_class_file() and require, and keeps the wrapper first in SPL. Optional takeover mode.
 * Version: 0.2.0
 */

// Turn this on to completely remove Jetpack's autoloader
// define( 'JP_AUTOLOADER_PROBE_TAKEOVER', true );

// Turn this on to see per-class and per file timings:
// define( 'JP_AUTOLOADER_PROBE_DETAIL', 'true' );

/** ------------------------------------------------------------------------
 * Minimal AC timers
 * --------------------------------------------------------------------- */
if ( ! function_exists( 'ac_start' ) ) {
	function ac_start( $label ) {
		if ( ! isset( $GLOBALS['ac_timings'][ $label ] ) ) {
			$GLOBALS['ac_timings'][ $label ] = [
				'count'   => 0,
				'total'   => 0.0,
				'min'     => PHP_INT_MAX,
				'max'     => 0.0,
				'samples' => [], // reservoir for median
			];
		}
		$GLOBALS['ac_timings'][ $label ]['start'] = hrtime( true );
	}
}

if ( ! function_exists( 'ac_stop' ) ) {
	function ac_stop( $label ) {
		$end = hrtime( true );
		if ( empty( $GLOBALS['ac_timings'][ $label ]['start'] ) ) {
			// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
			// error_log( "AC Debug Error: ac_stop('$label') called without a matching ac_start()" );
			return;
		}
		$duration = ( $end - $GLOBALS['ac_timings'][ $label ]['start'] ) / 1e6; // ms
		unset( $GLOBALS['ac_timings'][ $label ]['start'] );

		$slot = &$GLOBALS['ac_timings'][ $label ];
		$slot['count']++;
		$slot['total'] += $duration;
		$slot['min']    = min( $slot['min'], $duration );
		$slot['max']    = max( $slot['max'], $duration );

		// Reservoir sample up to 1000 for median
		if ( count( $slot['samples'] ) < 1000 ) {
			$slot['samples'][] = $duration;
		} elseif ( mt_rand( 0, $slot['count'] ) < 1000 ) {
			$slot['samples'][ mt_rand( 0, 999 ) ] = $duration;
		}
	}
}

if ( ! function_exists( 'ac_calculate_median' ) ) {
	function ac_calculate_median( $samples ) {
		$c = count( $samples );
		if ( ! $c ) {
			return 0.0;
		}
		sort( $samples, SORT_NUMERIC );
		$m = intdiv( $c - 1, 2 );
		return ( $c % 2 ) ? (float) $samples[ $m ] : ( $samples[ $m ] + $samples[ $m + 1 ] ) / 2.0;
	}
}

$GLOBALS['jp_probe'] = $GLOBALS['jp_probe'] ?? [ 'seen' => 0, 'found' => 0, 'required' => 0 ];

/** ------------------------------------------------------------------------
 * Helper: identify Jetpack autoloader callbacks in SPL chain
 * Jetpack's autoloader lives under a generated namespace prefix like:
 *   Automattic\Jetpack\Autoloader\jp123\PHP_Autoloader::load_class
 * --------------------------------------------------------------------- */
function jp_probe_is_jetpack_autoloader_callback( $cb ) {
	$ns = null;
	if ( is_string( $cb ) ) {
		$ns = $cb;
	} elseif ( is_array( $cb ) ) {
		$ns = is_string( $cb[0] ) ? $cb[0] : ( is_object( $cb[0] ) ? get_class( $cb[0] ) : null );
	}
	return is_string( $ns ) && strpos( $ns, 'Automattic\\Jetpack\\Autoloader\\jp' ) === 0;
}

/** ------------------------------------------------------------------------
 * Our autoload wrapper: mirrors Jetpack's load_class but adds timers
 * --------------------------------------------------------------------- */
function jp_autoloader_profiler_load( $class_name ) {
	$GLOBALS['jp_probe']['seen']++;

	global $jetpack_autoloader_loader;
	if ( ! isset( $jetpack_autoloader_loader ) || ! is_object( $jetpack_autoloader_loader ) ) {
		return false; // Not Jetpack-managed; let SPL continue
	}

	$detail = defined( 'JP_AUTOLOADER_PROBE_DETAIL' ) && JP_AUTOLOADER_PROBE_DETAIL;

	// --- find_class_file()
	if ( $detail ) {
		ac_start( "Find $class_name" );
	}
	ac_start( 'JP find_class_file' );
	$file = $jetpack_autoloader_loader->find_class_file( $class_name );
	ac_stop( 'JP find_class_file' );
	if ( $detail ) {
		ac_stop( "Find $class_name" );
	}

	if ( ! isset( $file ) ) {
		return false; // Not a Jetpack class after all
	}
	$GLOBALS['jp_probe']['found']++;

	// --- parity with Jetpack's early-load debug
	if (
		defined( 'JETPACK_AUTOLOAD_DEBUG_EARLY_LOADS' ) && JETPACK_AUTOLOAD_DEBUG_EARLY_LOADS &&
		( strpos( $file, '/vendor/' ) !== false || strpos( $file, '/jetpack_vendor/' ) !== false ) &&
		is_callable( 'did_action' ) && ! did_action( 'plugins_loaded' )
	) {
		$msg = "Jetpack Autoloader: Autoloading `$class_name` before the plugins_loaded hook may cause strange and confusing problems.";
		if ( function_exists( 'wp_debug_backtrace_summary' ) ) {
			$msg .= ' ' . wp_debug_backtrace_summary( '', 1 );
		}
		if ( is_callable( 'wp_trigger_error' ) ) {
			wp_trigger_error( '', $msg );
		} else {
			// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_trigger_error
			trigger_error( $msg );
		}
	}

	// --- require $file
	if ( $detail ) {
		ac_start( "Require $file" );
	}
	ac_start( 'JP require' );
	require $file;
	ac_stop( 'JP require' );
	if ( $detail ) {
		ac_stop( "Require $file" );
	}

	$GLOBALS['jp_probe']['required']++;
	return true;
}

/** ------------------------------------------------------------------------
 * Keep our wrapper in front
 * --------------------------------------------------------------------- */
function jp_autoloader_profiler_promote_front() {
	// Re-register our callback at the front. To guarantee "front", remove then add.
	$cb = 'jp_autoloader_profiler_load';
	$funcs = spl_autoload_functions();
	if ( is_array( $funcs ) ) {
		foreach ( $funcs as $fn ) {
			// Compare strictly; call_user_func performs loose equality for strings
			if ( $fn === $cb ) {
				spl_autoload_unregister( $cb );
				break;
			}
		}
	}
	spl_autoload_register( $cb, true, true ); // prepend=true
}

function jp_autoloader_profiler_takeover_if_enabled() {
	if ( ! defined( 'JP_AUTOLOADER_PROBE_TAKEOVER' ) || ! JP_AUTOLOADER_PROBE_TAKEOVER ) {
		return;
	}
	$funcs = spl_autoload_functions();
	if ( ! is_array( $funcs ) ) {
		return;
	}
	foreach ( $funcs as $fn ) {
		if ( jp_probe_is_jetpack_autoloader_callback( $fn ) ) {
			spl_autoload_unregister( $fn ); // remove Jetpack's autoloader; our wrapper now handles Jetpack classes
		}
	}
}

/** ------------------------------------------------------------------------
 * Boot: register early and keep reclaiming front as plugins load
 * --------------------------------------------------------------------- */
$__ac_jp_probe_boot = static function () {
	// Register once at the very beginning.
	spl_autoload_register( 'jp_autoloader_profiler_load', true, true );
	// In case someone already registered with prepend earlier, promote now.
	jp_autoloader_profiler_promote_front();
};

if ( function_exists( 'add_action' ) ) {
	// Earliest reliable point for MU plugins.
	add_action( 'muplugins_loaded', $__ac_jp_probe_boot, 1 );

	// After each plugin file is loaded, reclaim the front and optionally take over.
	add_action(
		'plugin_loaded',
		function ( $plugin ) {
			jp_autoloader_profiler_takeover_if_enabled();
			jp_autoloader_profiler_promote_front();
		},
		9999,
		1
	);

	// Safety net once all plugins are loaded.
	add_action(
		'plugins_loaded',
		function () {
			jp_autoloader_profiler_takeover_if_enabled();
			jp_autoloader_profiler_promote_front();
		},
		9999
	);
} else {
	// Non-WP
	$__ac_jp_probe_boot();
}

/** ------------------------------------------------------------------------
 * Shutdown log
 * --------------------------------------------------------------------- */
if ( function_exists( 'add_action' ) ) {
	add_action(
		'shutdown',
		function () {
			// Append a small coverage summary to the existing AC log block.
			$jp = $GLOBALS['jp_probe'] ?? [ 'seen' => 0, 'found' => 0, 'required' => 0 ];

			$coverage = sprintf(
				'JP probe coverage - seen: %d, found: %d, required: %d',
				(int) $jp['seen'],
				(int) $jp['found'],
				(int) $jp['required']
			);

			error_log( $coverage );
		},
		9999
	);
}

if ( function_exists( 'add_action' ) ) {
	add_action(
		'shutdown',
		function () {
			if ( empty( $GLOBALS['ac_timings'] ) ) {
				return;
			}

			$request_url = 'CLI';
			if ( isset( $_SERVER['REQUEST_URI'] ) ) {
				if ( function_exists( 'wp_unslash' ) && function_exists( 'esc_url_raw' ) ) {
					$request_url = esc_url_raw( wp_unslash( $_SERVER['REQUEST_URI'] ) );
				} else {
					$request_url = $_SERVER['REQUEST_URI'];
				}
			}

			$lines  = [ "AC Debug Summary for: $request_url" ];
			$format = '%-42s | %8s | %12s | %10s | %10s | %10s | %10s';
			$lines[] = sprintf( $format, 'Label', 'Count', 'Total (ms)', 'Avg (ms)', 'Median', 'Min', 'Max' );
			$lines[] = str_repeat( '-', 124 );

			$detail = defined( 'JP_AUTOLOADER_PROBE_DETAIL' ) && JP_AUTOLOADER_PROBE_DETAIL;

			foreach ( $GLOBALS['ac_timings'] as $label => $data ) {
				if ( empty( $data['count'] ) ) {
					continue;
				}

				if ( $detail && $data['total'] < 1 ) {
					continue;
				}

				$avg    = $data['total'] / $data['count'];
				$median = ac_calculate_median( $data['samples'] );
				$lines[] = sprintf(
					$format,
					substr( $label, 0, 42 ),
					(int) $data['count'],
					number_format( $data['total'], 2 ),
					number_format( $avg, 2 ),
					number_format( $median, 2 ),
					number_format( $data['min'], 2 ),
					number_format( $data['max'], 2 )
				);
			}
			$lines[]   = str_repeat( '-', 124 );
			$log_block = implode( "\n", $lines );

			if ( function_exists( 'has_action' ) && has_action( 'ac_debug_logged' ) ) {
				do_action( 'ac_debug_logged', $log_block );
			} else {
				// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
				error_log( $log_block );
			}
		},
		9999
	);
}

/**
 * ------------------------------------------------------------------------
 * Admin notice: remind that the profiler is active (admins only).
 * ------------------------------------------------------------------------
 */
if ( function_exists( 'add_action' ) ) {
	add_action( 'admin_init', 'jp_probe_notice_maybe_dismiss' );
	add_action( 'admin_notices', 'jp_probe_admin_notice' );
	add_action( 'network_admin_notices', 'jp_probe_admin_notice' );
}

function jp_probe_notice_maybe_dismiss() {
	if ( ! is_user_logged_in() ) {
		return;
	}
	if ( empty( $_GET['jp_probe_dismiss_notice'] ) ) {
		return;
	}
	// Verify and persist the dismissal for the current user.
	$nonce = isset( $_GET['_wpnonce'] ) ? $_GET['_wpnonce'] : '';
	if ( ! wp_verify_nonce( $nonce, 'jp_probe_dismiss_notice' ) ) {
		return;
	}
	update_user_meta( get_current_user_id(), 'jp_probe_notice_dismissed', 1 );

	// Clean the URL.
	wp_safe_redirect( remove_query_arg( array( 'jp_probe_dismiss_notice', '_wpnonce' ) ) );
	exit;
}

function jp_probe_admin_notice() {
	// Only in admin HTML views for site/network admins; skip AJAX/REST/cron.
	if ( ! is_admin() || wp_doing_ajax() || ! current_user_can( 'manage_options' ) ) {
		return;
	}
	if ( get_user_meta( get_current_user_id(), 'jp_probe_notice_dismissed', true ) ) {
		return;
	}

	$detail   = ( defined( 'JP_AUTOLOADER_PROBE_DETAIL' ) && JP_AUTOLOADER_PROBE_DETAIL ) ? 'on' : 'off';
	$takeover = ( defined( 'JP_AUTOLOADER_PROBE_TAKEOVER' ) && JP_AUTOLOADER_PROBE_TAKEOVER ) ? 'on' : 'off';
	$debug_on = ( defined( 'WP_DEBUG_LOG' ) && WP_DEBUG_LOG ) ? 'on' : 'off';

	$file_path  = function_exists( 'wp_normalize_path' ) ? wp_normalize_path( __FILE__ ) : __FILE__;
	$debug_path = ( defined( 'WP_CONTENT_DIR' ) ? WP_CONTENT_DIR . '/debug.log' : ABSPATH . 'wp-content/debug.log' );
	$debug_path = function_exists( 'wp_normalize_path' ) ? wp_normalize_path( $debug_path ) : $debug_path;

	$dismiss_url = wp_nonce_url( add_query_arg( 'jp_probe_dismiss_notice', '1' ), 'jp_probe_dismiss_notice' );

	echo '<div class="notice notice-warning is-dismissible">';
	echo '<p><strong>Jetpack Autoloader Profiler is active.</strong> Remember to remove it when you finish profiling.</p>';
	echo '<p>File: <code>' . esc_html( $file_path ) . '</code><br />';
	echo 'Log file: <code>' . esc_html( $debug_path ) . '</code><br />';
	echo 'Detail mode: <code>' . esc_html( $detail ) . '</code> · ';
	echo 'Takeover mode: <code>' . esc_html( $takeover ) . '</code> · ';
	echo 'WP_DEBUG_LOG: <code>' . esc_html( $debug_on ) . '</code></p>';
	echo '<p><a class="button button-secondary" href="' . esc_url( $dismiss_url ) . '">Dismiss for me</a></p>';
	echo '</div>';
}