use prescaling for collective (NVIDIA#1157)

apex/contrib/optimizers/distributed_fused_lamb.py

@@ -88,7 +88,7 @@ def __init__(self, params,
                  dwu_group_size=0, dwu_num_blocks=4, dwu_num_chunks=4,
                  dwu_num_rs_pg=1, dwu_num_ar_pg=4, dwu_num_ag_pg=0, fused_norm=False,
                  e5m2_allgather=False, verbose=False, clip_after_ar=True,
-                 full_ar=False):
+                 full_ar=False, fuse_scale=False):
         defaults = dict(lr=lr, bias_correction=bias_correction,
                         betas=betas, eps=eps, weight_decay=weight_decay,
                         grad_averaging=grad_averaging,
@@ -121,6 +121,7 @@ def __init__(self, params,
         self._verbose = verbose
         self._clip_after_ar = clip_after_ar
         self._full_ar = full_ar
+        self._fuse_scale = fuse_scale 
         self._L2_grad_norm = None
         self._fused_norm = fused_norm 
         self._current_process_group = c10d._get_default_group()
@@ -544,6 +545,17 @@ def _get_flush_block(self):
 
         return flush_block
 
+    def _full_all_reduce_scale(self, block_id, scale):
+        works = [None]*self._num_chunks
+
+        for chunk_id in range(self._num_chunks):
+            glob_chunk_id = block_id * self._num_chunks + chunk_id
+            ar_stream = self._ar_st[glob_chunk_id%self._num_ar_pg]
+            ar_stream.wait_stream(torch.cuda.current_stream())
+            with torch.cuda.stream(ar_stream):
+                works[chunk_id] = torch.distributed.all_reduce(self._flat_grads_chunks[block_id][chunk_id],group=self._ar_pg[glob_chunk_id%self._num_ar_pg],async_op=True,op=torch.distributed.make_nccl_premul_sum((scale,)))
+        self._reductions_works[block_id] = works
+
     def _full_all_reduce(self, block_id):
         works = [None]*self._num_chunks
 
@@ -555,6 +567,29 @@ def _full_all_reduce(self, block_id):
                 works[chunk_id] = torch.distributed.all_reduce(self._flat_grads_chunks[block_id][chunk_id],group=self._ar_pg[glob_chunk_id%self._num_ar_pg],async_op=True)
         self._reductions_works[block_id] = works
 
+    def _reduce_scatter_and_all_reduce_scale(self, block_id, scale):
+        # Reduction within each node
+        # Changes gradient format from [block * chunk * shard] to [shard * block * chunk]
+        # The output format is the same as the fp32 master parameters
+        works = [None]*self._num_chunks
+        for chunk_id in range(self._num_chunks):
+            glob_chunk_id = block_id * self._num_chunks + chunk_id
+            rs_stream = self._rs_st[glob_chunk_id%self._num_rs_pg]
+            rs_stream.wait_stream(torch.cuda.current_stream())
+            rs_stream.wait_stream(self._l2_grad_norm_st)
+            with torch.cuda.stream(rs_stream):
+                works[chunk_id] = torch.distributed.reduce_scatter(self._fp16_g_chunks[block_id][chunk_id],self._flat_grads_shards[block_id][chunk_id],group=self._rs_pg[glob_chunk_id%self._num_rs_pg],async_op=True,no_copy=True,op=torch.distributed.make_nccl_premul_sum((scale,)))
+
+        # Reduction across nodes for each rank
+        if self._num_groups > 1:
+            for chunk_id in range(self._num_chunks):
+                glob_chunk_id = block_id * self._num_chunks + chunk_id
+                ar_stream = self._ar_st[glob_chunk_id%self._num_ar_pg]
+                with torch.cuda.stream(ar_stream):
+                    works[chunk_id].wait()
+                    works[chunk_id] = torch.distributed.all_reduce(self._fp16_g_chunks[block_id][chunk_id],group=self._ar_pg[glob_chunk_id%self._num_ar_pg],async_op=True)
+        self._reductions_works[block_id] = works
+
     def _reduce_scatter_and_all_reduce(self, block_id):
         # Reduction within each node
         # Changes gradient format from [block * chunk * shard] to [shard * block * chunk]
@@ -620,12 +655,19 @@ def _pipeline_block_reductions(self, block_id):
             tmp = torch.cat(((self._one), (coeff)))
             index = (coeff+1>coeff).int()
             scale = tmp.index_select(0, index).half()/self._world_size
-            self._flat_grads.mul_(scale)
+            if not self._fuse_scale:
+                self._flat_grads.mul_(scale)
 
             if self._full_ar:
-                self._full_all_reduce(block_id)
+                if self._fuse_scale:
+                    self._full_all_reduce_scale(block_id, scale)
+                else:
+                    self._full_all_reduce(block_id) 
             else:
-                self._reduce_scatter_and_all_reduce(block_id)
+                if self._fuse_scale:
+                    self._reduce_scatter_and_all_reduce_scale(block_id, scale)
+                else:
+                    self._reduce_scatter_and_all_reduce(block_id)
 
             if block_id == 0:
                 for block_id in range(self._num_blocks):