reduce a copy for rowsparse parameter.reduce (apache#12039)

python/mxnet/gluon/parameter.py

@@ -319,7 +319,7 @@ def _reduce(self):
             # fetch all rows for 'row_sparse' param
             all_row_ids = ndarray.arange(0, self.shape[0], dtype='int64', ctx=ctx)
             data = ndarray.zeros(self.shape, stype='row_sparse', ctx=ctx)
-            self._trainer._row_sparse_pull(self, data, all_row_ids)
+            self._trainer._row_sparse_pull(self, data, all_row_ids, full_idx=True)
         return data
 
     def initialize(self, init=None, ctx=None, default_init=initializer.Uniform(),

python/mxnet/gluon/trainer.py

@@ -235,14 +235,21 @@ def set_learning_rate(self, lr):
         else:
             self._optimizer.set_learning_rate(lr)
 
-    def _row_sparse_pull(self, parameter, out, row_id):
+    def _row_sparse_pull(self, parameter, out, row_id, full_idx=False):
+        """Internal method to invoke pull operations on KVStore. If `full_idx` is set to True,
+        `kv.pull` is preferred instead of `kv.row_sparse_pull`.
+        """
         # initialize kv and params if not already
         if not self._kv_initialized:
             self._init_kvstore()
         if self._params_to_init:
             self._init_params()
         idx = self._param2idx[parameter.name]
-        self._kvstore.row_sparse_pull(idx, out=out, row_ids=row_id, priority=-idx)
+        if full_idx and 'dist' not in self._kvstore.type:
+            assert row_id.size == out.shape[0]
+            self._kvstore.pull(idx, out=out, priority=-idx, ignore_sparse=False)
+        else:
+            self._kvstore.row_sparse_pull(idx, out=out, row_ids=row_id, priority=-idx)
 
     def step(self, batch_size, ignore_stale_grad=False):
         """Makes one step of parameter update. Should be called after

tests/python/unittest/test_gluon_trainer.py

@@ -113,6 +113,24 @@ def test_trainer_save_load():
     # check if parameter dict is correctly associated with optimizer after load_state
     assert trainer._kvstore._updater.optimizer._get_lr(0) == 0.2
 
+@with_seed()
+def test_trainer_sparse_save_load():
+    x = gluon.Parameter('x', shape=(10, 1), lr_mult=1.0, stype='row_sparse')
+    x.initialize(ctx=[mx.cpu(0)], init='zeros')
+    trainer = gluon.Trainer([x], 'sgd', {'learning_rate': 0.1})
+    all_rows = mx.nd.arange(0, 10, ctx=mx.cpu(0))
+    with mx.autograd.record():
+        for w in x.list_row_sparse_data(all_rows):
+            y = w * 1
+            y.backward()
+    trainer.step(1)
+    assert trainer._kvstore._updater.optimizer._get_lr(0) == 0.1
+    trainer.save_states('test_trainer_sparse_save_load.states')
+    trainer.load_states('test_trainer_sparse_save_load.states')
+    x.lr_mult = 2.0
+    # check if parameter dict is correctly associated with optimizer after load_state
+    assert trainer._kvstore._updater.optimizer._get_lr(0) == 0.2
+
 @with_seed()
 def test_trainer_multi_layer_init():
     class Net(gluon.Block):
@@ -158,23 +176,6 @@ def check_init(ctxes):
     check_init([mx.cpu(1), mx.cpu(2)])
     check_init([mx.cpu(1)])
 
-@with_seed()
-def test_trainer_save_load():
-    x = gluon.Parameter('x', shape=(10,), lr_mult=1.0)
-    x.initialize(ctx=[mx.cpu(0), mx.cpu(1)], init='zeros')
-    trainer = gluon.Trainer([x], 'sgd', {'learning_rate': 0.1})
-    with mx.autograd.record():
-        for w in x.list_data():
-            y = w + 1
-            y.backward()
-    trainer.step(1)
-    assert trainer._kvstore._updater.optimizer._get_lr(0) == 0.1
-    trainer.save_states('test_trainer_save_load.states')
-    trainer.load_states('test_trainer_save_load.states')
-    x.lr_mult = 2.0
-    # check if parameter dict is correctly associated with optimizer after load_state
-    assert trainer._kvstore._updater.optimizer._get_lr(0) == 0.2
-
 @with_seed()
 def test_trainer_reset_kv():
     def check_trainer_reset_kv(kv):