--- a/core/lib/Drupal/Core/Cron.php	(revision bb41144fce32f42f69b763091cffd0dedd651e3e)
+++ b/core/lib/Drupal/Core/Cron.php	(revision )
@@ -2,6 +2,7 @@

 namespace Drupal\Core;

+use Drupal\Component\Utility\Timer;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Queue\QueueWorkerManagerInterface;
 use Drupal\Core\Queue\RequeueException;
@@ -192,8 +193,25 @@
    * Invokes any cron handlers implementing hook_cron.
    */
   protected function invokeCronHandlers() {
+    $module_previous = '';
+
     // Iterate through the modules calling their cron handlers (if any):
     foreach ($this->moduleHandler->getImplementations('cron') as $module) {
+
+      if (!$module_previous) {
+        $this->logger->notice('Starting execution of @module_cron().', [
+          '@module' => $module,
+        ]);
+      }
+      else {
+        $this->logger->notice('Starting execution of @module_cron(), execution of @module_previous_cron() took @time.', [
+          '@module' => $module,
+          '@module_previous' => $module_previous,
+          '@time' => Timer::read('cron_' . $module_previous) . 'ms',
+        ]);
+      }
+      Timer::start('cron_' . $module);
+
       // Do not let an exception thrown by one module disturb another.
       try {
         $this->moduleHandler->invoke($module, 'cron');
@@ -201,6 +219,9 @@
       catch (\Exception $e) {
         watchdog_exception('cron', $e);
       }
+
+      Timer::stop('cron_' . $module);
+      $module_previous = $module;
     }
   }

Index: core/modules/dblog/src/Tests/DbLogTest.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- core/modules/dblog/src/Tests/DbLogTest.php	(revision bb41144fce32f42f69b763091cffd0dedd651e3e)
+++ core/modules/dblog/src/Tests/DbLogTest.php	(revision )
@@ -116,10 +116,14 @@

     // Run a cron job.
     $this->cronRun();
+
+    // Get the number of enabled modules. Cron adds a log entry for each module.
+    $list = \Drupal::moduleHandler()->getModuleList();
+
     // Verify that the database log row count equals the row limit plus one
     // because cron adds a record after it runs.
     $count = db_query('SELECT COUNT(wid) FROM {watchdog}')->fetchField();
-    $this->assertTrue($count == $row_limit + 1, format_string('Dblog row count of @count equals row limit of @limit plus one', array('@count' => $count, '@limit' => $row_limit)));
+    $this->assertTrue($count == $row_limit + count($list) + 1, format_string('Dblog row count of @count equals row limit of @limit plus one', array('@count' => $count, '@limit' => $row_limit)));
   }

   /**