refactor: raise warning when gpu numbers is not 4

ppcls/engine/engine.py

@@ -231,11 +231,13 @@ class Engine(object):
                 save_dtype='float32')
 
         # for distributed
-        self.config["Global"][
-            "distributed"] = paddle.distributed.get_world_size() != 1
+        world_size = dist.get_world_size()
+        self.config["Global"]["distributed"] = world_size != 1
+        if world_size != 4 and self.mode == "train":
+            msg = f"The training strategy in config files provided by PaddleClas is based on 4 gpus. But the number of gpus is {world_size} in current training. Please modify the stategy (learning rate, batch size and so on) if use config files in PaddleClas to train."
+            logger.warning(msg)
         if self.config["Global"]["distributed"]:
             dist.init_parallel_env()
-        if self.config["Global"]["distributed"]:
             self.model = paddle.DataParallel(self.model)
 
         # build postprocess for infer
@@ -346,8 +348,8 @@ class Engine(object):
     @paddle.no_grad()
     def infer(self):
         assert self.mode == "infer" and self.eval_mode == "classification"
-        total_trainer = paddle.distributed.get_world_size()
-        local_rank = paddle.distributed.get_rank()
+        total_trainer = dist.get_world_size()
+        local_rank = dist.get_rank()
         image_list = get_image_list(self.config["Infer"]["infer_imgs"])
         # data split
         image_list = image_list[local_rank::total_trainer]