Allow to scale LR in different ways. (#1167)

Author: shishaochen

deepmd/train/trainer.py

@@ -157,6 +157,13 @@ def _init_param(self, jdata):
 
         # learning rate
         lr_param = j_must_have(jdata, 'learning_rate')
+        scale_by_worker = lr_param.get('scale_by_worker', 'linear')
+        if scale_by_worker == 'linear':
+            self.scale_lr_coef = float(self.run_opt.world_size)
+        elif scale_by_worker == 'sqrt':
+            self.scale_lr_coef = np.sqrt(self.run_opt.world_size).real
+        else:
+            self.scale_lr_coef = 1.
         lr_type = lr_param.get('type', 'exp')
         if lr_type == 'exp':
             self.lr = LearningRateExp(lr_param['start_lr'],
@@ -330,7 +337,11 @@ def _build_network(self, data):
     def _build_training(self):
         trainable_variables = tf.trainable_variables()
         if self.run_opt.is_distrib:
-            optimizer = tf.train.AdamOptimizer(learning_rate = self.learning_rate*self.run_opt.world_size)
+            if self.scale_lr_coef > 1.:
+                log.info('Scale learning rate by coef: %f', self.scale_lr_coef)
+                optimizer = tf.train.AdamOptimizer(self.learning_rate*self.scale_lr_coef)
+            else:
+                optimizer = tf.train.AdamOptimizer(self.learning_rate)
             optimizer = self.run_opt._HVD.DistributedOptimizer(optimizer)
         else:
             optimizer = tf.train.AdamOptimizer(learning_rate = self.learning_rate)

deepmd/utils/argcheck.py

@@ -452,8 +452,10 @@ def learning_rate_variant_type_args():
 
 
 def learning_rate_args():
+    doc_scale_by_worker = 'When parallel training or batch size scaled, how to alter learning rate. Valid values are `linear`(default), `sqrt` or `none`.'
     doc_lr = "The definitio of learning rate" 
-    return Argument("learning_rate", dict, [], 
+    return Argument("learning_rate", dict,
+                    [Argument("scale_by_worker", str, optional=True, default='linear', doc=doc_scale_by_worker)],
                     [learning_rate_variant_type_args()],
                     doc = doc_lr)
 

doc/train/parallel-training.md

@@ -3,9 +3,19 @@
 Currently, parallel training is enabled in a sychoronized way with help of [Horovod](https://github.com/horovod/horovod).
 Depend on the number of training processes (according to MPI context) and number of GPU cards avaliable, DeePMD-kit will decide whether to launch the training in parallel (distributed) mode or in serial mode. Therefore, no additional options is specified in your JSON/YAML input file.
 
-Horovod works in the data-parallel mode, resulting in a larger global batch size. For example, the real batch size is 8 when `batch_size` is set to 2 in the input file and you launch 4 workers. Thus, `learning_rate` is automatically scaled by the number of workers for better convergence. The number of decay steps required to achieve same accuracy will also reduce based on the number of cards (e.g., 1/4 of steps in the above case), but needs to be scaled manually in the input file.
+## Tuning learning rate
 
-Technical details of such heuristic rule are discussed at [Accurate, Large Minibatch SGD: Training ImageNet in 1 Hour](https://arxiv.org/abs/1706.02677).
+Horovod works in the data-parallel mode, resulting in a larger global batch size. For example, the real batch size is 8 when `batch_size` is set to 2 in the input file and you launch 4 workers. Thus, `learning_rate` is automatically scaled by the number of workers for better convergence. Technical details of such heuristic rule are discussed at [Accurate, Large Minibatch SGD: Training ImageNet in 1 Hour](https://arxiv.org/abs/1706.02677).
+
+The number of decay steps required to achieve same accuracy can decrease by the number of cards (e.g., 1/2 of steps in the above case), but needs to be scaled manually in the input file.
+
+In some cases, it won't work well when scale learning rate by worker count in a `linear` way. Then you can try `sqrt` or `none` by setting argument `scale_by_worker` like below.
+```json
+    "learning_rate" :{
+        "scale_by_worker": "none",
+        "type": "exp"
+    }
+```
 
 ## Scaling test