Merge branch 'main' into docstr

Author: sonichi

flaml/automl.py

@@ -1590,7 +1590,13 @@ def custom_metric(
         self._n_concurrent_trials = n_concurrent_trials
         self._early_stop = early_stop
         self._use_ray = use_ray or n_concurrent_trials > 1
-        self._hpo_method = hpo_method or ("bs" if self._use_ray else "cfo")
+        # use the following condition if we have an estimation of average_trial_time and average_trial_overhead
+        # self._use_ray = use_ray or n_concurrent_trials > ( average_trail_time + average_trial_overhead) / (average_trial_time)
+        self._hpo_method = hpo_method or (
+            "bs"
+            if n_concurrent_trials > 1 or self._use_ray and len(estimator_list) > 1
+            else "cfo"
+        )
         if log_file_name:
             with training_log_writer(log_file_name, append_log) as save_helper:
                 self._training_log = save_helper