Add Sequence Parallelism to llama

Somehow the torch.compile not working although eager sequence
parallelism working, so currently don't turn it on by default

ghstack-source-id: 0d251f2
Pull Request resolved: #32

Author: wanchaol

torchtrain/models/llama/model.py

@@ -211,7 +211,10 @@ def forward(
             torch.Tensor: Output tensor after attention.
 
         """
-        bsz, seqlen, _ = x.shape
+        seqlen, _ = freqs_cis.shape
+        bs_seqlen, _ = x.shape
+        bsz = bs_seqlen // seqlen
+
         xq, xk, xv = self.wq(x), self.wk(x), self.wv(x)
 
         xq = xq.view(bsz, seqlen, self.n_heads, self.head_dim)
@@ -237,7 +240,8 @@ def forward(
         output = output.transpose(
             1, 2
         ).contiguous()  # (bs, seqlen, n_local_heads, head_dim)
-        output = output.view(bsz, seqlen, -1)
+        # output stay folded with batch and sequence dimension
+        output = output.view(bsz * seqlen, -1)
         return self.wo(output)
 
 
@@ -342,7 +346,6 @@ def __init__(self, layer_id: int, args: ModelArgs):
         super().__init__()
         self.n_heads = args.n_heads
         self.dim = args.dim
-        self.head_dim = args.dim // args.n_heads
         self.attention = Attention(args)
         self.feed_forward = FeedForward(
             dim=args.dim,
@@ -422,10 +425,17 @@ def forward(self, tokens: torch.Tensor):
 
         """
         h, freqs_cis = self.embeddings(tokens)
+        # fold batch and sequence dimension for more efficient allgather/reduce_scatter
+        h = h.view(-1, self.params.dim)
 
         for layer in self.layers:
             h = layer(h, freqs_cis)
+
         h = self.norm(h)
+        # unfold batch and sequence dimension
+        bsz = tokens.shape[0]
+        bs_seqlen = h.shape[0]
+        h = h.view(bsz, bs_seqlen // bsz, self.params.dim)
         output = self.output(h).float()
         return output
 

torchtrain/parallelisms/parallelize_llama.py

@@ -7,6 +7,13 @@
 import logging
 
 import torch
+from torch.distributed._tensor import (
+    distribute_module,
+    distribute_tensor,
+    DTensor,
+    Replicate,
+    Shard,
+)
 
 from torch.distributed.algorithms._checkpoint.checkpoint_wrapper import (
     checkpoint_wrapper as ptd_checkpoint_wrapper,
@@ -19,11 +26,46 @@
     ShardingStrategy,
 )
 from torch.distributed.fsdp.wrap import enable_wrap, wrap
+from torch.distributed.tensor.parallel import (
+    ColwiseParallel,
+    parallelize_module,
+    PrepareModuleInput,
+    RowwiseParallel,
+)
 
 from torchtrain.logging_utils import rank0_log
 
 logger = logging.getLogger(__name__)
 
+
+def distribute_rmsnorm(module, device_mesh):
+    # temp sharding API until PTD API is added
+    def prepare_input_fn(inputs, device_mesh):
+        if isinstance(inputs[0], DTensor):
+            return inputs
+        elif isinstance(inputs[0], torch.Tensor):
+            shard_tensor = DTensor.from_local(
+                inputs[0], device_mesh, [Shard(0)], run_check=False
+            )
+            return shard_tensor
+        else:
+            raise NotImplementedError("!!")
+
+    def partition_fn(name, module, device_mesh):
+        for name, param in module.named_parameters():
+            dist_param = torch.nn.Parameter(
+                distribute_tensor(param, device_mesh, [Replicate()])
+            )
+            module.register_parameter(name, dist_param)
+
+    return distribute_module(
+        module,
+        device_mesh,
+        partition_fn,
+        input_fn=prepare_input_fn,
+    )
+
+
 # Uses PTD FSDP AC wrapper
 def checkpoint_wrapper(module, config):
     return ptd_checkpoint_wrapper(
@@ -43,7 +85,75 @@ def parallelize_llama(model, world_mesh, parallel_dims, args):
     if parallel_dims.pp_enabled:
         raise NotImplementedError("PP not implemented yet.")
     if parallel_dims.sp_enabled:
-        raise NotImplementedError("SP not implemented yet.")
+        # First we apply Sequence Parallelism if it's enabled
+        tp_mesh = world_mesh["sp"] if world_mesh.ndim > 1 else world_mesh
+        sp_degree = args.sp_degree
+        # First:
+        # 1. parallelize the first embedding and the last linear proj layer
+        # 2. shard the first layer of transformer block
+        # TODO: enable loss parallel once it's ready
+        model = parallelize_module(
+            model,
+            tp_mesh,
+            {
+                "embeddings.tok_embeddings": RowwiseParallel(
+                    input_layouts=Replicate(),
+                ),
+                "output": ColwiseParallel(
+                    input_layouts=Shard(0),
+                    output_layouts=Replicate(),
+                ),
+                "layers.0": PrepareModuleInput(
+                    input_layouts=(Replicate(), None),
+                    desired_input_layouts=(Shard(0), None),
+                    use_local_output=True,
+                ),
+            },
+        )
+
+        # apply sequence parallelism to every transformer block
+        for layer_id, transformer_block in enumerate(model.layers):
+            layer_plan = {
+                "attention": PrepareModuleInput(
+                    input_layouts=(Shard(0), None),
+                    desired_input_layouts=(Replicate(), None),
+                ),
+                "attention.wq": ColwiseParallel(),
+                "attention.wk": ColwiseParallel(),
+                "attention.wv": ColwiseParallel(),
+                "attention.wo": RowwiseParallel(output_layouts=Shard(0)),
+                "feed_forward": PrepareModuleInput(
+                    input_layouts=(Shard(0),),
+                    desired_input_layouts=(Replicate(),),
+                ),
+                "feed_forward.w1": ColwiseParallel(),
+                "feed_forward.w2": RowwiseParallel(output_layouts=Shard(0)),
+                "feed_forward.w3": ColwiseParallel(),
+            }
+            # if layer_id == 0:
+            #     # in first transformer block we need to shard the input
+            #     layer_plan[""] = PrepareModuleInput(
+            #         input_layouts=(Replicate(), None),
+            #         desired_input_layouts=(Shard(0), None),
+            #     )
+
+            # adjust num_heads in attention layer to local heads
+            attn_layer = transformer_block.attention
+            attn_layer.n_heads = attn_layer.n_heads // sp_degree
+            attn_layer.n_kv_heads = attn_layer.n_kv_heads // sp_degree
+
+            # shard RMSNorm layers
+            distribute_rmsnorm(transformer_block.attention_norm, tp_mesh)
+            distribute_rmsnorm(transformer_block.ffn_norm, tp_mesh)
+
+            parallelize_module(
+                module=transformer_block,
+                device_mesh=tp_mesh,
+                parallelize_plan=layer_plan,
+            )
+
+        rank0_log("Applied Sequence Parallelism to the model...")
+
     if parallel_dims.dp_enabled:
         dp_mesh = world_mesh["dp"] if world_mesh.ndim > 1 else world_mesh
         assert dp_mesh.mesh_dim_names == ["dp"], dp_mesh.mesh_dim_names
@@ -73,6 +183,6 @@ def parallelize_llama(model, world_mesh, parallel_dims, args):
             # wrap the rest layers with FSDP
             model = wrap(model.cuda())
 
-    rank0_log("Applied parallelisms to the model...")
+        rank0_log("Applied FSDP to the model...")
 
     return model