fix next_tokens of controller (#20060)

* fix next_tokens of controller

python/paddle/fluid/contrib/slim/nas/light_nas_strategy.py

@@ -133,11 +133,18 @@ class LightNASStrategy(Strategy):
                 self._retrain_epoch == 0 or
             (context.epoch_id - self.start_epoch) % self._retrain_epoch == 0):
             _logger.info("light nas strategy on_epoch_begin")
+            min_flops = -1
             for _ in range(self._max_try_times):
                 startup_p, train_p, test_p, _, _, train_reader, test_reader = context.search_space.create_net(
                     self._current_tokens)
                 context.eval_graph.program = test_p
                 flops = context.eval_graph.flops()
+                if min_flops == -1:
+                    min_flops = flops
+                    min_tokens = self._current_tokens[:]
+                else:
+                    if flops < min_flops:
+                        min_tokens = self._current_tokens[:]
                 if self._max_latency > 0:
                     latency = context.search_space.get_model_latency(test_p)
                     _logger.info("try [{}] with latency {} flops {}".format(
@@ -147,7 +154,8 @@ class LightNASStrategy(Strategy):
                         self._current_tokens, flops))
                 if flops > self._max_flops or (self._max_latency > 0 and
                                                latency > self._max_latency):
-                    self._current_tokens = self._search_agent.next_tokens()
+                    self._current_tokens = self._controller.next_tokens(
+                        min_tokens)
                 else:
                     break
 

python/paddle/fluid/contrib/slim/searcher/controller.py

@@ -123,11 +123,14 @@ class SAController(EvolutionaryController):
         _logger.info("current_reward: {}; current tokens: {}".format(
             self._reward, self._tokens))
 
-    def next_tokens(self):
+    def next_tokens(self, control_token=None):
         """
         Get next tokens.
         """
-        tokens = self._tokens
+        if control_token:
+            tokens = control_token[:]
+        else:
+            tokens = self._tokens
         new_tokens = tokens[:]
         index = int(len(self._range_table) * np.random.random())
         new_tokens[index] = (