private function simpleWarmUp() {
    // Warm up frequent requests.
    $this->request(['query' => ['classes' => TRUE]]);
    $locations = $this->request(['query' => ['locations' => TRUE]]);

    // Warm up cache for current day for all locations.
    $timezone = new \DateTimeZone($this->configFactory->get('system.date')->get('timezone')['default']);
    $datetime = new \DateTime('today midnight', $timezone);
    $start = $datetime->getTimestamp();
    $end = $datetime->add(new \DateInterval('P1D'))->getTimestamp();
    foreach ($locations as $location) {
      $options = [
        'query' => [
          'schedule' => TRUE,
          'desc' => "true",
          'location' => [(string) $location->id],
          'start' => $start,
          'end' => $end,
        ]
      ];
      $this->request($options);
    }
  }