[zero] add unit testings for hybrid parallelism (#2486)

Author: 1SAA

colossalai/zero/sharded_optim/bookkeeping/bucket_store.py

@@ -7,7 +7,6 @@ class BucketStore(BaseStore):
 
     def __init__(self, torch_pg: ProcessGroup):
         super().__init__(torch_pg)
-        self._grads = dict()
         self._params = dict()
         self._num_elements_in_bucket = dict()
 
@@ -19,25 +18,24 @@ def num_elements_in_bucket(self, reduce_rank: int = None):
     def add_num_elements_in_bucket(self, num_elements, reduce_rank: int = None):
         self._num_elements_in_bucket[reduce_rank] += num_elements
 
-    def add_grad(self, tensor, reduce_rank: int = None):
-        self._grads[reduce_rank].append(tensor)
-
     def add_param(self, tensor, reduce_rank: int = None):
         self._params[reduce_rank].append(tensor)
 
     def reset(self):
         keys = [None] + list(range(self._world_size))
-        self._grads = {rank: [] for rank in keys}
         self._params = {rank: [] for rank in keys}
         self._num_elements_in_bucket = {rank: 0 for rank in keys}
 
     def reset_by_rank(self, reduce_rank=None):
-        self._grads[reduce_rank] = []
         self._params[reduce_rank] = []
         self._num_elements_in_bucket[reduce_rank] = 0
 
     def get_grad(self, reduce_rank: int = None):
-        return self._grads[reduce_rank]
+        param_list = self.get_param(reduce_rank)
+        for param in param_list:
+            # the param must have grad for reduction
+            assert param.grad is not None, f'Parameter of size ({param.size()}) has None grad, cannot be reduced'
+        return [param.grad for param in param_list]
 
     def get_param(self, reduce_rank: int = None):
         return self._params[reduce_rank]

colossalai/zero/sharded_optim/low_level_optim.py

@@ -46,7 +46,7 @@ def __init__(
             reduce_bucket_size: int = 1024 * 1024,    # communication
             communication_dtype: Optional[torch.dtype] = None,
             overlap_communication: bool = False,
-            partition_grad: bool = False,    # stage 2
+            partition_grad: bool = False,    # stage 2 flag
             cpu_offload: bool = False,    # cpu offload
             forced_dtype: Optional[torch.dtype] = None):
 
@@ -248,9 +248,13 @@ def _partition_param_list(self, param_list):
             self._logger.info(f'Number of elements on ranks: {numel_per_rank}', ranks=[0])
         return params_per_rank
 
-    ###########################################################
-    # Backward Reduction Hook
-    ###########################################################
+    ###########################
+    # Backward Reduction Hook #
+    ###########################
+
+    def _grad_handler(self, param, grad, reduce_rank):
+        self._add_to_reduction_bucket(param, reduce_rank)
+        return grad
 
     def _attach_reduction_hook(self):
         # we iterate over the fp16 params
@@ -268,53 +272,61 @@ def _attach_reduction_hook(self):
                     else:
                         reduce_rank = None
 
-                    def _define_and_attach(param, reduce_rank):
-                        # get the AccumulateGrad object of the param itself
-                        accum_grad_obj = get_grad_accumulate_object(param)
-                        self._grad_store.add_accumulate_grad_object(accum_grad_obj)
+                    param.register_hook(partial(self._grad_handler, param, reduce_rank=reduce_rank))
 
-                        reduction_func = partial(self._reduce_and_remove_grads_by_bucket,
-                                                 param=param,
-                                                 reduce_rank=reduce_rank)
+    def _reduce_tensor_bucket(self, bucket: TensorBucket, reduce_rank):
+        if self._overlap_communication:
+            torch.cuda.synchronize()
+            self._param_store.clear_grads_of_previous_reduced_params()
+            stream = self._comm_stream
+        else:
+            stream = torch.cuda.current_stream()
 
-                        # define hook
-                        # NOT IMPORTANT BUT GOOD TO KNOW:
-                        # args here is not grad, but allow_unreacable and accumulate_grad
-                        def reduce_grad_hook(*args):
-                            reduction_func()
+        with torch.cuda.stream(stream):
+            flat = bucket.flatten()
+            reduce_global_rank = None
+            if reduce_rank is not None:
+                reduce_global_rank = self._dp_global_ranks[reduce_rank]
+            reduced_flat = reduce_tensor_dp_group(tensor=flat,
+                                                  dtype=self._communication_dtype,
+                                                  dst_local_rank=reduce_rank,
+                                                  dst_global_rank=reduce_global_rank,
+                                                  group=self._dp_torch_group)
 
-                        accum_grad_obj.register_hook(reduce_grad_hook)
+            # update the reduced tensor
+            if reduce_rank is None or reduce_rank == self._local_rank:
+                bucket.unflatten_and_copy(reduced_flat)
 
-                    _define_and_attach(param, reduce_rank)
+    def _reduce_tensor_list_with_one_dtype(self, tensor_list, bucket_size, reduce_rank):
+        param_bucket = TensorBucket(size=bucket_size)
 
-    def _reduce_and_remove_grads_by_bucket(self, param, reduce_rank=None):
-        param_size = param.numel()
+        for tensor in tensor_list:
+            param_bucket.add_to_bucket(tensor, allow_oversize=True)
 
-        # check if the bucket is full
-        # if full, will reduce the grads already in the bucket
-        # after reduction, the bucket will be empty
-        if self._bucket_store.num_elements_in_bucket(reduce_rank) + param_size > self._reduce_bucket_size:
-            self._reduce_grads_in_bucket(reduce_rank)
+            if param_bucket.is_full_or_oversized():
+                self._reduce_tensor_bucket(bucket=param_bucket, reduce_rank=reduce_rank)
+                param_bucket.empty()
 
-        # the param must not be reduced to ensure correctness
-        is_param_reduced = self._param_store.is_param_reduced(param)
-        if is_param_reduced:
-            msg = f'Parameter of size ({param.size()}) has already been reduced, ' \
-                  + 'duplicate reduction will lead to arithmetic incorrectness'
-            raise RuntimeError(msg)
+        if not param_bucket.is_empty():
+            self._reduce_tensor_bucket(bucket=param_bucket, reduce_rank=reduce_rank)
 
-        # the param must have grad for reduction
-        assert param.grad is not None, f'Parameter of size ({param.size()}) has None grad, cannot be reduced'
+    def _reduce_grads(self, reduce_rank, grads, bucket_size):
+        grad_buckets_by_dtype = split_half_float_double(grads)
 
-        self._bucket_store.add_num_elements_in_bucket(param_size, reduce_rank)
-        self._bucket_store.add_grad(param.grad, reduce_rank)
-        self._bucket_store.add_param(param, reduce_rank)
+        for tensor_list in grad_buckets_by_dtype:
+            self._reduce_tensor_list_with_one_dtype(tensor_list=tensor_list,
+                                                    bucket_size=bucket_size,
+                                                    reduce_rank=reduce_rank)
+
+    #######################
+    # Reduction Functions #
+    #######################
 
-    def _reduce_grads_in_bucket(self, reduce_rank=None):
+    def _run_reduction(self, reduce_rank=None):
         # reduce grads
-        self._reduce_grads_by_rank(reduce_rank=reduce_rank,
-                                   grads=self._bucket_store.get_grad(reduce_rank=reduce_rank),
-                                   bucket_size=self._bucket_store.num_elements_in_bucket(reduce_rank))
+        self._reduce_grads(reduce_rank=reduce_rank,
+                           grads=self._bucket_store.get_grad(reduce_rank=reduce_rank),
+                           bucket_size=self._bucket_store.num_elements_in_bucket(reduce_rank))
 
         # use communication stream if overlapping
         # communication with computation
@@ -351,50 +363,24 @@ def _reduce_grads_in_bucket(self, reduce_rank=None):
 
         self._bucket_store.reset_by_rank(reduce_rank)
 
-    def _reduce_grads_by_rank(self, reduce_rank, grads, bucket_size):
-        grad_buckets_by_dtype = split_half_float_double(grads)
-
-        for tensor_list in grad_buckets_by_dtype:
-            self._reduce_no_retain(tensor_list=tensor_list, bucket_size=bucket_size, reduce_rank=reduce_rank)
-
-    ##############################
-    # Reduction Utility Function #
-    ##############################
-    def _reduce_no_retain(self, tensor_list, bucket_size, reduce_rank):
-        param_bucket = TensorBucket(size=bucket_size)
-
-        for tensor in tensor_list:
-            param_bucket.add_to_bucket(tensor, allow_oversize=True)
-
-            if param_bucket.is_full_or_oversized():
-                self._reduce_and_copy(bucket=param_bucket, reduce_rank=reduce_rank)
-                param_bucket.empty()
-
-        if not param_bucket.is_empty():
-            self._reduce_and_copy(bucket=param_bucket, reduce_rank=reduce_rank)
+    def _add_to_reduction_bucket(self, param, reduce_rank=None):
+        param_size = param.numel()
 
-    def _reduce_and_copy(self, bucket: TensorBucket, reduce_rank):
-        if self._overlap_communication:
-            torch.cuda.synchronize()
-            self._param_store.clear_grads_of_previous_reduced_params()
-            stream = self._comm_stream
-        else:
-            stream = torch.cuda.current_stream()
+        # check if the bucket is full
+        # if full, will reduce the grads already in the bucket
+        # after reduction, the bucket will be empty
+        if self._bucket_store.num_elements_in_bucket(reduce_rank) + param_size > self._reduce_bucket_size:
+            self._run_reduction(reduce_rank)
 
-        with torch.cuda.stream(stream):
-            flat = bucket.flatten()
-            reduce_global_rank = None
-            if reduce_rank is not None:
-                reduce_global_rank = self._dp_global_ranks[reduce_rank]
-            reduced_flat = reduce_tensor_dp_group(tensor=flat,
-                                                  dtype=self._communication_dtype,
-                                                  dst_local_rank=reduce_rank,
-                                                  dst_global_rank=reduce_global_rank,
-                                                  group=self._dp_torch_group)
+        # the param must not be reduced to ensure correctness
+        is_param_reduced = self._param_store.is_param_reduced(param)
+        if is_param_reduced:
+            msg = f'Parameter of size ({param.size()}) has already been reduced, ' \
+                  + 'duplicate reduction will lead to arithmetic incorrectness'
+            raise RuntimeError(msg)
 
-            # update the reduced tensor
-            if reduce_rank is None or reduce_rank == self._local_rank:
-                bucket.unflatten_and_copy(reduced_flat)
+        self._bucket_store.add_num_elements_in_bucket(param_size, reduce_rank)
+        self._bucket_store.add_param(param, reduce_rank)
 
     ################################
     # torch.optim.Optimizer methods
@@ -498,8 +484,9 @@ def step(self, closure=None):
         # broadcast the updated model weights
         handles = []
         for group_id in range(self.num_param_groups):
-            for rank in range(self._world_size):
-                fp16_param = self._param_store.get_flat_fp16_param_by_rank_group(rank=rank, group_id=group_id)
+            for index in range(self._world_size):
+                rank = self._dp_global_ranks[index]
+                fp16_param = self._param_store.get_flat_fp16_param_by_rank_group(rank=index, group_id=group_id)
                 handle = dist.broadcast(fp16_param, src=rank, group=self._dp_torch_group, async_op=True)
                 handles.append(handle)
 
@@ -585,16 +572,16 @@ def _reduce_grad_stage1(self):
                 param_group = self._fp16_param_groups[group_id]
                 for param in param_group:
                     if param.grad is not None:
-                        self._reduce_and_remove_grads_by_bucket(param)
+                        self._add_to_reduction_bucket(param)
 
         # we need to reduce the gradients
         # left in the communication bucket
-        self._reduce_grads_in_bucket()
+        self._run_reduction()
 
     def _reduce_grad_stage2(self):
         # when partition_grads is True, reduction hooks
         # are attached in the __init__ function, so we
         # only need to reduce the gradients
         # left in the communication bucket
         for reduce_rank in range(self._world_size):
-            self._reduce_grads_in_bucket(reduce_rank)
+            self._run_reduction(reduce_rank)

tests/test_tensor/common_utils/_utils.py

@@ -4,6 +4,7 @@
 import numpy as np
 import torch
 import torch.distributed as dist
+from torch.testing import assert_close
 
 from colossalai.context import ParallelMode
 from colossalai.core import global_context as gpc
@@ -41,14 +42,20 @@ def broadcast_tensor_chunk(tensor, chunk_size=1, local_rank=0):
     return tensor_chunk.clone()
 
 
-def tensor_equal(A, B):
-    return torch.allclose(A, B, rtol=1e-3, atol=1e-1)
+def tensor_equal(t_a: torch.Tensor, t_b: torch.Tensor, rtol: float = 1e-3, atol: float = 1e-1):
+    assert_close(t_a, t_b, rtol=rtol, atol=atol)
+    return True
 
 
-def tensor_shard_equal(tensor: torch.Tensor, shard: torch.Tensor, rank, world_size):
+def tensor_shard_equal(tensor: torch.Tensor,
+                       shard: torch.Tensor,
+                       rank: int,
+                       world_size: int,
+                       rtol: float = 1e-3,
+                       atol: float = 1e-1):
     assert tensor.ndim == shard.ndim
     if tensor.shape == shard.shape:
-        return tensor_equal(tensor, shard)
+        return tensor_equal(tensor, shard, rtol, atol)
     else:
         dims_not_eq = torch.nonzero(torch.tensor(tensor.shape) != torch.tensor(shard.shape))
         if dims_not_eq.numel() == 1:
@@ -58,7 +65,7 @@ def tensor_shard_equal(tensor: torch.Tensor, shard: torch.Tensor, rank, world_si
                 world_size = gpc.get_world_size(ParallelMode.PARALLEL_1D)
             if rank is None:
                 rank = gpc.get_local_rank(ParallelMode.PARALLEL_1D)
-            return tensor_equal(tensor.chunk(world_size, dim)[rank], shard)
+            return tensor_equal(tensor.chunk(world_size, dim)[rank], shard, rtol, atol)
         else:
             raise NotImplementedError