diff --git a/admin/tool/behat/cli/init.php b/admin/tool/behat/cli/init.php
index 5547b56eae3..97d613556d0 100644
--- a/admin/tool/behat/cli/init.php
+++ b/admin/tool/behat/cli/init.php
@@ -40,10 +40,41 @@ define('CACHE_DISABLE_ALL', true);
 require_once(__DIR__ . '/../../../../lib/clilib.php');
 require_once(__DIR__ . '/../../../../lib/behat/lib.php');
 
+
+list($options, $unrecognized) = cli_get_params(
+    array(
+        'parallel' => 0,
+        'suffix' => '',
+    )
+);
+
+
+$nproc = (int) preg_filter('#.*(\d+).*#', '$1', $options['parallel']);
+$suffixarg = $options['suffix'] ? "--suffix={$options['suffix']} --parallel=$nproc" : '';
+
+
+if ($nproc && !$suffixarg) {
+    foreach ((array)glob(__DIR__."/../../../../behat*") as $dir) {
+        if (file_exists($dir) && is_link($dir) && preg_match('#/behat\d+$#', $dir)) {
+            unlink($dir);
+        }
+    }
+    $cmds = array();
+    for ($i = 1; $i <= $nproc; $i++) {
+        $cmds[] = "php ".__FILE__." --suffix=$i --parallel=$nproc 2>&1";
+    }
+    // This is intensive compared to behat itself so halve the parallelism.
+    foreach (array_chunk($cmds, max(1, floor($nproc/2)), true) as $chunk) {
+        ns_parallel_popen($chunk, true);
+    }
+    exit(0);
+}
+
+
 // Changing the cwd to admin/tool/behat/cli.
 chdir(__DIR__);
 $output = null;
-exec("php util.php --diag", $output, $code);
+exec("php util.php --diag $suffixarg", $output, $code);
 if ($code == 0) {
     echo "Behat test environment already installed\n";
 
@@ -53,7 +84,7 @@ if ($code == 0) {
 
     // Behat and dependencies are installed and we need to install the test site.
     chdir(__DIR__);
-    passthru("php util.php --install", $code);
+    passthru("php util.php --install $suffixarg", $code);
     if ($code != 0) {
         exit($code);
     }
@@ -64,12 +95,12 @@ if ($code == 0) {
 
     // Test site data is outdated.
     chdir(__DIR__);
-    passthru("php util.php --drop", $code);
+    passthru("php util.php --drop $suffixarg", $code);
     if ($code != 0) {
         exit($code);
     }
 
-    passthru("php util.php --install", $code);
+    passthru("php util.php --install $suffixarg", $code);
     if ($code != 0) {
         exit($code);
     }
@@ -81,7 +112,7 @@ if ($code == 0) {
 
     // Returning to admin/tool/behat/cli.
     chdir(__DIR__);
-    passthru("php util.php --install", $code);
+    passthru("php util.php --install $suffixarg", $code);
     if ($code != 0) {
         exit($code);
     }
@@ -93,7 +124,7 @@ if ($code == 0) {
 }
 
 // Enable editing mode according to config.php vars.
-passthru("php util.php --enable", $code);
+passthru("php util.php --enable $suffixarg", $code);
 if ($code != 0) {
     exit($code);
 }
diff --git a/admin/tool/behat/cli/ns_parallel.php b/admin/tool/behat/cli/ns_parallel.php
new file mode 100644
index 00000000000..2f1ae7e7cfc
--- /dev/null
+++ b/admin/tool/behat/cli/ns_parallel.php
@@ -0,0 +1,212 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Wrapper to run previously set-up behat tests in parallel.
+ *
+ * @package    tool_behat
+ * @copyright  2014 NetSpot Pty Ltd
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+
+if (isset($_SERVER['REMOTE_ADDR'])) {
+    die(); // No access from web!
+}
+
+
+define('BEHAT_UTIL', true);
+define('CLI_SCRIPT', true);
+define('ABORT_AFTER_CONFIG', true);
+define('NO_OUTPUT_BUFFERING', true);
+
+error_reporting(E_ALL | E_STRICT);
+ini_set('display_errors', '1');
+ini_set('log_errors', '1');
+
+
+require_once __DIR__ .'/../../../../config.php';
+require_once __DIR__.'/../../../../lib/clilib.php';
+require_once __DIR__.'/../../../../lib/behat/lib.php';
+
+
+list($options, $unrecognised) = cli_get_params(
+    array(
+        'stop-on-failure' => 0,
+        'parallel' => 0,
+        'verbose' => false,
+        'replace' => false,
+    )
+);
+
+
+if (empty($options['parallel']) && $dirs = glob("{$CFG->dirroot}/behat*")) {
+    sort($dirs);
+    if ($max = preg_filter('#.*behat(\d+)#', '$1', end($dirs))) {
+        $options['parallel'] = $max;
+    }
+}
+
+
+$suffix = '';
+$time = microtime(true);
+$nproc = (int) preg_filter('#.*(\d+).*#', '$1', $options['parallel']);
+array_walk($unrecognised, function (&$v) {
+    if ($x = preg_filter("#^(-+\w+)=(.+)#", "\$1='\$2'", $v)) {
+        $v = $x;
+    } else if (!preg_match("#^-#", $v)) {
+        $v = escapeshellarg($v);
+    }
+});
+$extraopts = implode(' ', $unrecognised);
+
+
+if (empty($nproc)) {
+    fwrite(STDERR, "Invalid or missing --parallel parameter, must be >= 1.\n");
+    exit(1);
+}
+
+
+$checkfail = array();
+$outputs = array();
+$handles = array();
+$pipe2i = array();
+$exits = array();
+$unused = null;
+$linelencnt = 0;
+$procs = array();
+
+
+for ($i = 1; $i <= $nproc; $i++) {
+    $myopts = !empty($options['replace']) ? str_replace($options['replace'], $i, $extraopts) : $extraopts;
+    $dirroot = dirname($CFG->behat_dataroot)."/behat$i";
+    $cmd = "exec {$CFG->dirroot}/vendor/bin/behat --config $dirroot/behat/behat.yml $myopts";
+    list($handle, $pipes) = ns_proc_open($cmd, true);
+    @fclose($pipes[0]);
+    unset($pipes[0]);
+    $exits[$i] = 1;
+    $handles[$i] = array($handle, $pipes[1], $pipes[2]);
+    $procs[$i] = $handle;
+    $checkfail[$i] = false;
+    $outputs[$i] = array('');
+    $pipe2i[(int) $pipes[1]] = $i;
+    $pipe2i[(int) $pipes[2]] = $i;
+    stream_set_blocking($pipes[1], 0);
+    stream_set_blocking($pipes[2], 0);
+}
+
+
+while (!empty($procs)) {
+    usleep(10000);
+
+    foreach ($handles as $i => $p) {
+        if (!($status = @proc_get_status($p[0])) || !$status['running']) {
+            if ($exits[$i] !== 0) {
+                $exits[$i] = !empty($status) ? $status['exitcode'] : 1;
+            }
+            unset($procs[$i]);
+            unset($handles[$i][0]);
+            $last = array_pop($outputs[$i]);
+            for ($l=2; $l>=1; $l--)
+                while ($part = @fread($handles[$i][$l], 8192))
+                    $last .= $part;
+            $outputs[$i] = array_merge($outputs[$i], explode("\n", $last));
+        }
+    }
+
+    $ready = array();
+    foreach ($handles as $i => $set) {
+        $ready[] = $set[1];
+        $ready[] = $set[2];
+    }
+
+    // Poll for any process with output or ended.
+    if (!$result = @stream_select($ready, $unused, $unused, 1)) {
+        // Nothing; try again.
+        continue;
+    }
+    if (!$fh = reset($ready)) {
+        continue;
+    }
+
+    $i = $pipe2i[(int) $fh];
+    $last = array_pop($outputs[$i]);
+    $read = fread($fh, 4096);
+    $newlines = explode("\n", $last.$read);
+    $outputs[$i] = array_merge($outputs[$i], $newlines);
+
+    if (!$checkfail[$i]) {
+        foreach ($newlines as $l => $line) {
+            unset($newlines[$l]);
+            if (preg_match('#^Started at [\d\-]+#', $line) || (strlen($line) > 3 && preg_match('#^\s*([FS\.\-]+)(?:\s+\d+)?\s*$#', $line))) {
+                $checkfail[$i] = true;
+                break;
+            }
+        }
+    }
+    if ($progress = preg_filter('#^\s*([FUS\.\-]+)(?:\s+\d+)?\s*$#', '$1', $newlines)) {
+        if ($checkfail[$i] && preg_filter('#^\s*[S\.\-]*[FU][S\.\-]*(?:\s+\d+)?\s*$#', '$1', $progress)) {
+            $exits[$i] = 1;
+            if ($options['stop-on-failure']) {
+                foreach ($handles as $l => $p) {
+                    $exits[$l] = $l != $i ? 0 : $exits[$i];
+                    @proc_terminate($p[0], SIGINT);
+                }
+            }
+        }
+    }
+    // Process has gone, assume this is the last output for it.
+    if (empty($procs[$i])) {
+        unset($handles[$i]);
+    }
+    if (empty($checkfail[$i]) || !($update = preg_filter('#^\s*([FS\.\-]+)(?:\s+\d+)?\s*$#', '$1', $read))) {
+        continue;
+    }
+    while ($update) {
+        $part = substr($update, 0, 70 - $linelencnt);
+        $update = substr($update, strlen($part));
+        $linelencnt += strlen($part);
+        echo $part;
+        if ($linelencnt >= 70) {
+            echo "\n";
+            $linelencnt = 0;
+        }
+    }
+}
+echo "\n\n";
+
+
+$exits = array_filter($exits, function ($v) {return $v !== 0;});
+
+
+if ($exits || $options['verbose']) {
+    echo "Exit codes: ".implode(" ", $exits)."\n\n";
+    foreach ($outputs as $i => $output) {
+        unset($outputs[$i]);
+        if (!end($output)) array_pop($output);
+        $prefix = "[behat$i] ";
+        array_walk($output, function (&$l) use ($prefix) {
+            $l = $prefix.$l;
+        });
+        echo implode("\n", $output)."\n\n";
+    }
+    $failed = true;
+}
+
+
+$time = round(microtime(true) - $time, 1);
+echo "Finished in {$time}s\n";
+exit(!empty($failed) ? 1 : 0);
diff --git a/admin/tool/behat/cli/util.php b/admin/tool/behat/cli/util.php
index d843bf2fb6b..b68992e3701 100644
--- a/admin/tool/behat/cli/util.php
+++ b/admin/tool/behat/cli/util.php
@@ -40,6 +40,8 @@ list($options, $unrecognized) = cli_get_params(
     array(
         'help'    => false,
         'install' => false,
+        'parallel' => 0,
+        'suffix' => '',
         'drop'    => false,
         'enable'  => false,
         'disable' => false,
@@ -63,6 +65,7 @@ Options:
 --drop     Drops the database tables and the dataroot contents
 --enable   Enables test environment and updates tests list
 --disable  Disables test environment
+--parallel  Run operation for all parallel behat environments.
 --diag     Get behat test environment status code
 
 -h, --help     Print out this help
@@ -78,11 +81,32 @@ if (!empty($options['help'])) {
     exit(0);
 }
 
-// Describe this script.
+
+if (!empty($options['parallel']) && empty($options['suffix'])) {
+    foreach ((array)glob(__DIR__."/../../../../behat*") as $dir) {
+        if (file_exists($dir) && is_dir($dir)) {
+            unlink($dir);
+        }
+    }
+    $cmds = array();
+    $extra = preg_filter('#(.*)\s*--parallel=\d+\s*(.*?)#', '$1 $2', implode(' ', array_slice($argv, 1)));
+    for ($i = 1; $i <= $options['parallel']; $i++) {
+        $cmds[] = "php ".__FILE__." $extra --suffix=$i 2>&1";
+    }
+    // This is intensive compared to behat itself so halve the parallelism.
+    foreach (array_chunk($cmds, min(1, floor($options['parallel']/2)), true) as $chunk) {
+        ns_parallel_popen($chunk, true);
+    }
+    exit(0);
+}
+
+
+// Checking $CFG->behat_* vars and values.
 define('BEHAT_UTIL', true);
 define('CLI_SCRIPT', true);
 define('NO_OUTPUT_BUFFERING', true);
 define('IGNORE_COMPONENT_CACHE', true);
+define('BEHAT_SUFFIX', $options['suffix']);
 
 // Only load CFG from config.php, stop ASAP in lib/setup.php.
 define('ABORT_AFTER_CONFIG', true);
diff --git a/behat_pga_default.json b/behat_pga_default.json
new file mode 100644
index 00000000000..dbce41d24e3
--- /dev/null
+++ b/behat_pga_default.json
@@ -0,0 +1,109 @@
+{
+    "course\/tests\/behat\/course_controls.feature": 117.2,
+    "backup\/util\/ui\/tests\/behat\/restore_moodle2_courses.feature": 108.2,
+    "mod\/forum\/tests\/behat\/discussion_subscriptions.feature": 92.8,
+    "course\/tests\/behat\/category_resort.feature": 75.4,
+    "course\/tests\/behat\/course_resort.feature": 58.9,
+    "admin\/tool\/behat\/tests\/behat\/data_generators.feature": 53.1,
+    "course\/tests\/behat\/category_management.feature": 50.1,
+    "blocks\/recent_activity\/tests\/behat\/structural_changes.feature": 48.3,
+    "grade\/tests\/behat\/grade_override_letter.feature": 47.3,
+    "blocks\/activity_modules\/tests\/behat\/block_activity_modules.feature": 42.7,
+    "calendar\/tests\/behat\/calendar.feature": 42,
+    "grade\/grading\/form\/rubric\/tests\/behat\/edit_rubric.feature": 41.2,
+    "mod\/forum\/tests\/behat\/forum_subscriptions.feature": 32.6,
+    "course\/tests\/behat\/move_activities.feature": 30.8,
+    "mod\/workshep\/tests\/behat\/workshep_assessment.feature": 29.3,
+    "blocks\/glossary_random\/tests\/behat\/glossary_random.feature": 29,
+    "mod\/workshop\/tests\/behat\/workshop_assessment.feature": 28.8,
+    "blocks\/tests\/behat\/manage_blocks.feature": 28.6,
+    "badges\/tests\/behat\/navrequirecap.feature": 28,
+    "mod\/quiz\/tests\/behat\/completion_condition_attempts_used.feature": 26.9,
+    "mod\/quiz\/tests\/behat\/completion_condition_passing_grade.feature": 26,
+    "blocks\/html\/tests\/behat\/multiple_instances.feature": 26,
+    "message\/tests\/behat\/display_history.feature": 24.7,
+    "course\/tests\/behat\/category_change_visibility.feature": 24.2,
+    "local\/uneditableblocks\/tests\/behat\/enable_uneditableblocks.feature": 23.1,
+    "mod\/feedback\/tests\/behat\/defaultshortanswerlength.feature": 22.1,
+    "backup\/util\/ui\/tests\/behat\/backup_courses.feature": 22,
+    "course\/tests\/behat\/create_delete_course.feature": 21.9,
+    "blocks\/course_summary\/tests\/behat\/block_course_summary_course.feature": 21.2,
+    "course\/tests\/behat\/move_sections.feature": 21.1,
+    "course\/tests\/behat\/course_category_management_listing.feature": 21,
+    "local\/userpolicy\/tests\/behat\/fieldvisibility.feature": 20.9,
+    "admin\/tool\/behat\/tests\/behat\/get_and_set_fields.feature": 20.5,
+    "mod\/wiki\/tests\/behat\/edit_tags.feature": 19.6,
+    "mod\/attendance\/tests\/behat\/attendance_mod.feature": 19.5,
+    "blocks\/participants\/tests\/behat\/block_participants_course.feature": 19.5,
+    "blocks\/course_summary\/tests\/behat\/block_course_summary_frontpage.feature": 17.7,
+    "blocks\/tests\/behat\/configure_block_throughout_site.feature": 17.7,
+    "grade\/report\/singleview\/tests\/behat\/singleview.feature": 17.6,
+    "grade\/grading\/form\/rubric\/tests\/behat\/reuse_own_rubrics.feature": 16.3,
+    "mod\/wiki\/tests\/behat\/group_enhancements.feature": 16.2,
+    "admin\/tests\/behat\/forcelogin_makefrontpagepublic.feature": 16,
+    "message\/tests\/behat\/disablenotifications.feature": 16,
+    "completion\/tests\/behat\/teacher_manual_completion.feature": 16,
+    "mod\/glossary\/tests\/behat\/entries_require_approval.feature": 16,
+    "backup\/util\/ui\/tests\/behat\/import_course.feature": 15.9,
+    "admin\/tests\/behat\/set_admin_settings_value.feature": 15.8,
+    "mod\/mediagallery\/tests\/behat\/separategroups.feature": 15.6,
+    "blocks\/tests\/behat\/return_block_original_state.feature": 15.6,
+    "admin\/tests\/behat\/custom_maxbytes.feature": 15.4,
+    "mod\/oublog\/tests\/behat\/separate_individuals.feature": 15.4,
+    "mod\/forum\/tests\/behat\/default_displaywordcount.feature": 15.4,
+    "backup\/util\/ui\/tests\/behat\/restore_moodle2_course_numsections.feature": 14.9,
+    "question\/tests\/behat\/question_defaultpenalty.feature": 14.8,
+    "availability\/tests\/behat\/edit_availability.feature": 14.7,
+    "mod\/data\/tests\/behat\/view_entries.feature": 14.6,
+    "local\/catdelete\/tests\/behat\/catdelete.feature": 14.3,
+    "group\/tests\/behat\/showusernameingroup.feature": 14.3,
+    "mod\/forum\/tests\/behat\/edit_post_student.feature": 14.2,
+    "admin\/tool\/behat\/tests\/behat\/nasty_strings.feature": 14.1,
+    "mod\/hsuforum\/tests\/behat\/edit_post_student.feature": 13.8,
+    "mod\/quiz\/tests\/behat\/add_quiz.feature": 13.5,
+    "grade\/grading\/form\/rubric\/tests\/behat\/publish_rubric_templates.feature": 13.5,
+    "blocks\/autocreate_user\/tests\/behat\/add_introtext.feature": 13.5,
+    "question\/type\/truefalse\/tests\/behat\/custompenalty.feature": 13.3,
+    "blocks\/participants\/tests\/behat\/block_participants_frontpage.feature": 13.1,
+    "blocks\/html\/tests\/behat\/course_block.feature": 12.9,
+    "mod\/quiz\/tests\/behat\/configsubnethide.feature": 12.8,
+    "mod\/forum\/tests\/behat\/separate_group_single_group_discussions.feature": 12.6,
+    "blocks\/html\/tests\/behat\/configuring_html_block.feature": 12.3,
+    "course\/tests\/behat\/course_change_visibility.feature": 12.2,
+    "course\/tests\/behat\/modchooser_hidden.feature": 11.9,
+    "blocks\/login\/tests\/behat\/login_block.feature": 11.7,
+    "course\/tests\/behat\/paged_course_navigation.feature": 11.1,
+    "course\/tests\/behat\/limitrolerenaming.feature": 11,
+    "mod\/book\/tests\/behat\/create_chapters.feature": 11,
+    "mod\/forum\/tests\/behat\/my_forum_posts.feature": 10.7,
+    "auth\/tests\/behat\/login.feature": 10.5,
+    "blocks\/glossary_random\/tests\/behat\/glossary_random_frontpage.feature": 10.5,
+    "mod\/data\/tests\/behat\/add_entries.feature": 10.1,
+    "mod\/wiki\/tests\/behat\/preview_page.feature": 9.7,
+    "mod\/oublog\/tests\/behat\/personalblog.feature": 9.7,
+    "admin\/tests\/behat\/display_short_names.feature": 9.6,
+    "mod\/forum\/tests\/behat\/separate_group_discussions.feature": 9.5,
+    "course\/tests\/behat\/add_activities.feature": 9.4,
+    "mod\/forum\/tests\/behat\/forum_subscriptions_management.feature": 8.8,
+    "blocks\/tests\/behat\/restrict_available_blocks.feature": 8.7,
+    "blocks\/comments\/tests\/behat\/add_comment.feature": 8.7,
+    "mod\/survey\/tests\/behat\/survey_types.feature": 8.5,
+    "admin\/tool\/langimport\/tests\/behat\/manage_langpacks.feature": 7.3,
+    "local\/rolerenaming\/tests\/behat\/course_role_renaming.feature": 7.2,
+    "course\/tests\/behat\/edit_settings.feature": 7.1,
+    "group\/tests\/behat\/create_groups.feature": 6.8,
+    "blocks\/tests\/behat\/add_blocks.feature": 6.5,
+    "message\/tests\/behat\/manage_contacts.feature": 6.1,
+    "course\/tests\/behat\/course_search.feature": 6,
+    "course\/tests\/behat\/course_creation.feature": 5.8,
+    "my\/tests\/behat\/reset_page.feature": 5.4,
+    "my\/tests\/behat\/restrict_available_blocks.feature": 5.3,
+    "mod\/oublog\/tests\/behat\/basic.feature": 5.2,
+    "my\/tests\/behat\/add_blocks.feature": 4.6,
+    "user\/tests\/behat\/reset_page.feature": 4,
+    "message\/tests\/behat\/search_history.feature": 3.9,
+    "blocks\/navigation\/tests\/behat\/expand_my_courses_setting.feature": 3.3,
+    "user\/tests\/behat\/add_blocks.feature": 2.8,
+    "report\/usersessions\/tests\/behat\/usersessions_report.feature": 2.7,
+    "admin\/tool\/behat\/tests\/behat\/test_environment.feature": 1
+}
\ No newline at end of file
diff --git a/lib/behat/classes/behat_config_manager.php b/lib/behat/classes/behat_config_manager.php
index d6c852017de..b6f97154999 100644
--- a/lib/behat/classes/behat_config_manager.php
+++ b/lib/behat/classes/behat_config_manager.php
@@ -79,7 +79,10 @@ class behat_config_manager {
                     $featurespaths[$uniquekey] = $path;
                 }
             }
-            $features = array_values($featurespaths);
+            foreach ($featurespaths as $path) {
+                $additional = glob("$path/*.feature");
+                $features = array_merge($features, $additional);
+            }
         }
 
         // Optionally include features from additional directories.
@@ -198,6 +201,29 @@ class behat_config_manager {
         // We require here when we are sure behat dependencies are available.
         require_once($CFG->dirroot . '/vendor/autoload.php');
 
+        $instance = 1;
+        $parallel = 0;
+        foreach ($_SERVER['argv'] as $arg) {
+            if (strpos($arg, '--suffix=') === 0) {
+                $instance = intval(substr($arg, strlen('--suffix=')));
+            }
+            if (empty($parallel)) {
+                $parallel = preg_filter('#--parallel=(\d+)#', '$1', $arg);
+            }
+        }
+
+        // Attempt to split into weighted buckets using timing information, if available.
+        if ($alloc = self::profile_guided_allocate($features, max(1, $parallel), $instance)) {
+            $features = $alloc;
+        } else {
+            // Divide the list of feature files amongst the parallel runners.
+            srand(crc32(floor(time() / 3600 / 24).var_export($features,true)));
+            shuffle($features);
+            // Pull out the features for just this worker.
+            $features = array_chunk($features, ceil(count($features) / max(1, $parallel)));
+            $features = $features[$instance-1];
+        }
+
         // It is possible that it has no value as we don't require a full behat setup to list the step definitions.
         if (empty($CFG->behat_wwwroot)) {
             $CFG->behat_wwwroot = 'http://itwillnotbeused.com';
@@ -242,6 +268,71 @@ class behat_config_manager {
         return Symfony\Component\Yaml\Yaml::dump($config, 10, 2);
     }
 
+    /**
+     * Attempt to split feature list into fairish buckets using timing information, if available.
+     * Simply add each one to lightest buckets until all files allocated.
+     * PGA = Profile Guided Allocation. I made it up just now.
+     * CAUTION: workers must agree on allocation, do not be random anywhere!
+     * 
+     * @param array $features Behat feature files array
+     * @param int $nbuckets Number of buckets to divide into
+     * @param int $instance Index number of this instance
+     * @return array Feature files array, sorted into allocations
+     */
+    protected static function profile_guided_allocate($features, $nbuckets, $instance) {
+        $pga = __DIR__.'/../../../behat_pga_default.json';
+        $pga = defined('BEHAT_PGA_DATA') && file_exists(BEHAT_PGA_DATA) ? BEHAT_PGA_DATA : $pga;
+
+        if (defined('BEHAT_PGA_DISABLE') || !file_exists($pga) || !$pga = @json_decode(file_get_contents($pga), true)) {
+            // No data available, fall back to relying on shuffle.
+            return false;
+        }
+
+        arsort($pga); // Ensure most expensive is first.
+
+        $realroot = realpath(__DIR__.'/../../../').'/';
+        $defaultweight = array_sum($pga) / count($pga); // TODO: median is more ideal.
+        $weights = array_fill(0, $nbuckets, 0);
+        $buckets = array_fill(0, $nbuckets, array());
+        $totalweight = 0;
+
+        // Re-key the features list to match pga data.
+        foreach ($features as $k => $file) {
+            $key = str_replace($realroot, '', $file);
+            $features[$key] = $file;
+            unset($features[$k]);
+            if (!isset($pga[$key])) {
+                $pga[$key] = $defaultweight;
+            }
+        }
+
+        // Sort features by known weights; largest ones should be allocated first.
+        $pgaorder = array();
+        foreach ($features as $key => $file) {
+            $pgaorder[$key] = $pga[$key];
+        }
+        arsort($pgaorder);
+
+        // Finally, add each feature one by one to the lightest bucket.
+        foreach ($pgaorder as $key => $weight) {
+            $file = $features[$key];
+            $light_bucket = array_search(min($weights), $weights);
+            $weights[$light_bucket] += $weight;
+            $buckets[$light_bucket][] = $file;
+            $totalweight += $weight;
+        }
+
+        if (!defined('BEHAT_PGA_DISABLE_HISTOGRAM') && $instance == $nbuckets) {
+            echo "Bucket weightings:\n";
+            foreach ($weights as $k => $weight) {
+                echo "$k: ".str_repeat('*', 70 * $nbuckets * $weight / $totalweight)."\n";
+            }
+        }
+
+        // Return the features for this worker.
+        return $buckets[$instance-1];
+    }
+
     /**
      * Overrides default config with local config values
      *
diff --git a/lib/behat/classes/util.php b/lib/behat/classes/util.php
index 95f42fea62d..4a42c578653 100644
--- a/lib/behat/classes/util.php
+++ b/lib/behat/classes/util.php
@@ -213,6 +213,22 @@ class behat_util extends testing_util {
         // Updates all the Moodle features and steps definitions.
         behat_config_manager::update_config_file();
 
+        // Create suffix symlink if necessary.
+        global $CFG;
+        if ($CFG->behat_suffix) {
+            $extra = preg_filter('#.*/(.+)$#', '$1', $CFG->behat_wwwroot);
+            $link = $CFG->dirroot.'/'.$extra;
+            if (file_exists($link)) {
+                if (!is_link($link)) {
+                    throw new coding_exception("File exists at link location ($link) but is not a link!");
+                }
+                @unlink($link);
+            }
+            if (!symlink($CFG->dirroot, $link)) {
+                throw new coding_exception("Unable to create behat suffix symlink ($link)");
+            }
+        }
+
         if (self::is_test_mode_enabled()) {
             return;
         }
diff --git a/lib/behat/lib.php b/lib/behat/lib.php
index 86718a92a8a..40612f4cd8e 100644
--- a/lib/behat/lib.php
+++ b/lib/behat/lib.php
@@ -272,6 +272,34 @@ function behat_is_test_site() {
     return false;
 }
 
+/**
+ * Add behat suffix to $CFG vars for parallel testing.
+ **/
+function behat_add_suffix_to_vars($suffix = '') {
+    global $CFG;
+
+    if (empty($suffix)) {
+        if (!empty($CFG->behat_suffix)) {
+            $suffix = $CFG->behat_suffix;
+
+        } else if (defined('BEHAT_SUFFIX') && BEHAT_SUFFIX) {
+            $suffix = BEHAT_SUFFIX;
+        }
+    }
+
+    $CFG->behat_suffix = $suffix;
+
+    if ($suffix) {
+        if (isset($CFG->behat_wwwroot) && !preg_match("#/behat$suffix\$#", $CFG->behat_wwwroot)) {
+            $CFG->behat_wwwroot .= "/behat{$suffix}";
+        }
+        if (!preg_match("#/behat{$suffix}\$#", $CFG->behat_dataroot)) {
+            $CFG->behat_dataroot = dirname($CFG->behat_dataroot)."/behat{$suffix}";
+        }
+        $CFG->behat_prefix = "behat{$suffix}_";
+    }
+}
+
 /**
  * Checks if the URL requested by the user matches the provided argument
  *
diff --git a/lib/clilib.php b/lib/clilib.php
index 32272defc04..e4992528144 100644
--- a/lib/clilib.php
+++ b/lib/clilib.php
@@ -175,3 +175,34 @@ function cli_error($text, $errorcode=1) {
     fwrite(STDERR, "\n");
     die($errorcode);
 }
+
+
+function ns_proc_open($cmd, $die = false) {
+    $desc = array(
+        0 => array('pipe', 'r'),
+        1 => array('pipe', 'w'),
+        2 => array('pipe', 'w'),
+    );
+    if (!($handle = proc_open($cmd, $desc, $pipes)) && $die) {
+        throw new Exception('Error starting worker');
+    }
+    return array($handle, $pipes);
+}
+
+
+function ns_parallel_popen($cmds, $doexit = false) {
+    $procs = array();
+    foreach ($cmds as $k => $cmd) {
+        $procs[] = popen($cmd, 'r');
+    }
+    $status = false;
+    foreach ($procs as $p) {
+        if (!$p) continue;
+        while ($out = fgets($p)) echo $out;
+        $status |= (bool) pclose($p);
+    }
+    if ($doexit && $status) {
+        exit($status);
+    }
+    return $status;
+}
diff --git a/lib/setup.php b/lib/setup.php
index d0a77601fdf..a0d870795d1 100644
--- a/lib/setup.php
+++ b/lib/setup.php
@@ -77,9 +77,34 @@ if (defined('BEHAT_SITE_RUNNING')) {
     // We already switched to behat test site previously.
 
 } else if (!empty($CFG->behat_wwwroot) or !empty($CFG->behat_dataroot) or !empty($CFG->behat_prefix)) {
+    global $argv;
+    $suffix = '';
+
+    if (defined('BEHAT_SUFFIX') && BEHAT_SUFFIX) {
+        $suffix = BEHAT_SUFFIX;
+
+    } else if (!empty($_SERVER['REMOTE_ADDR'])) {
+        if (preg_match('#/behat(.+?)/#', $_SERVER['REQUEST_URI'])) {
+            $afterpath = str_replace(realpath($CFG->dirroot).'/', '', realpath($_SERVER['SCRIPT_FILENAME']));
+            if (!$suffix = preg_filter("#.*/behat(.+?)/$afterpath#", '$1', $_SERVER['SCRIPT_FILENAME'])) {
+                throw new coding_exception("Unable to determine behat suffix [afterpath=$afterpath, scriptfilename={$_SERVER['SCRIPT_FILENAME']}]!");
+            }
+        }
+
+    } else if (defined('BEHAT_TEST') || defined('BEHAT_UTIL')) {
+        if ($match = preg_filter('#--suffix=(.+)#', '$1', $argv)) {
+            $suffix = reset($match);
+        }
+        if ($k = array_search('--config', $argv)) {
+            $behatconfig = $argv[$k+1];
+            $suffix = preg_filter("#^{$CFG->behat_dataroot}(.+?)/behat/behat\.yml#", '$1', $behatconfig);
+        }
+    }
+
     // The behat is configured on this server, we need to find out if this is the behat test
     // site based on the URL used for access.
     require_once(__DIR__ . '/../lib/behat/lib.php');
+    behat_add_suffix_to_vars($suffix);
     if (behat_is_test_site()) {
         // Checking the integrity of the provided $CFG->behat_* vars and the
         // selected wwwroot to prevent conflicts with production and phpunit environments.
@@ -89,7 +114,7 @@ if (defined('BEHAT_SITE_RUNNING')) {
         if (!file_exists("$CFG->behat_dataroot/behattestdir.txt")) {
             if ($dh = opendir($CFG->behat_dataroot)) {
                 while (($file = readdir($dh)) !== false) {
-                    if ($file === 'behat' or $file === '.' or $file === '..' or $file === '.DS_Store') {
+                    if ($file === 'behat' or $file === '.' or $file === '..' or $file === '.DS_Store' or is_numeric($file)) {
                         continue;
                     }
                     behat_error(BEHAT_EXITCODE_CONFIG, '$CFG->behat_dataroot directory is not empty, ensure this is the directory where you want to install behat test dataroot');
diff --git a/lib/testing/lib.php b/lib/testing/lib.php
index c089c6a76cf..bbb93d3e293 100644
--- a/lib/testing/lib.php
+++ b/lib/testing/lib.php
@@ -156,6 +156,9 @@ function testing_error($errorcode, $text = '') {
 
     // do not write to error stream because we need the error message in PHP exec result from web ui
     echo($text."\n");
+    if (isset($_SERVER['REMOTE_ADDR'])) {
+        header('HTTP/1.1 500 Internal Server Error');
+    }
     exit($errorcode);
 }
 
diff --git a/lib/tests/behat/behat_hooks.php b/lib/tests/behat/behat_hooks.php
index 6e2653f9ed6..060998294f8 100644
--- a/lib/tests/behat/behat_hooks.php
+++ b/lib/tests/behat/behat_hooks.php
@@ -153,6 +153,43 @@ class behat_hooks extends behat_base {
         }
     }
 
+    protected static $timings = array();
+
+    /** @BeforeFeature */
+    public static function before_feature($obj) {
+        $file = $obj->getFeature()->getFile();
+        self::$timings[$file] = microtime(true);
+    }
+
+    /** @AfterFeature */
+    public static function teardownFeature($obj) {
+        $file = $obj->getFeature()->getFile();
+        self::$timings[$file] = microtime(true) - self::$timings[$file];
+        // Probably didn't actually run this, don't output it.
+        if (self::$timings[$file] < 1) {
+            unset(self::$timings[$file]);
+        }
+    }
+
+    /** @AfterSuite */
+    public static function tearDown($obj) {
+        global $CFG;
+        if (!defined('BEHAT_FEATURE_TIMING')) {
+            return;
+        }
+        $realroot = realpath(__DIR__.'/../../../').'/';
+        foreach (self::$timings as $k => $v) {
+            $new = str_replace($realroot, '', $k);
+            self::$timings[$new] = round($v, 1);
+            unset(self::$timings[$k]);
+        }
+        if ($existing = @json_decode(file_get_contents(BEHAT_FEATURE_TIMING), true)) {
+            self::$timings = array_merge($existing, self::$timings);
+        }
+        arsort(self::$timings);
+        @file_put_contents(BEHAT_FEATURE_TIMING, json_encode(self::$timings, JSON_PRETTY_PRINT));
+    }
+
     /**
      * Resets the test environment.
      *