wgrad-accumulation patch for legacy megatron-LM (#451)

* wgrad-accumulation patch for legacy megatron-LM
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* fix
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Fix
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Fix fused attention tests
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

---------
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

tests/pytorch/test_fused_attn.py

@@ -648,7 +648,7 @@ class _dpa_fp8(torch.autograd.Function):
         ZInv = None
         philox_unpacked = None
 
-        qkv_out = ext.fp8_gemm(
+        qkv_out, _ = ext.fp8_gemm(
             qkv_weight_fp8,
             fp8_meta["scaling_fwd"].scale_inv,
             tex.FP8FwdTensors.GEMM1_WEIGHT,
@@ -798,7 +798,7 @@ class _dpa_fp8(torch.autograd.Function):
             )
 
             # QKV DGRAD
-            qkv_dgrad = ext.fp8_gemm(
+            qkv_dgrad, _ = ext.fp8_gemm(
                 qkv_weight_t_fp8,
                 fwd_scale_inverses,
                 tex.FP8FwdTensors.GEMM1_WEIGHT,
@@ -812,7 +812,7 @@ class _dpa_fp8(torch.autograd.Function):
                 use_split_accumulator=_2X_ACC_DGRAD,
             )
             # QKV WGRAD
-            qkv_wgrad = ext.fp8_gemm(
+            qkv_wgrad, _ = ext.fp8_gemm(
                 inputmat_t,
                 fwd_scale_inverses,
                 tex.FP8FwdTensors.GEMM1_INPUT,

transformer_engine/pytorch/module/layernorm_linear.py

@@ -473,14 +473,20 @@ class _LayerNormLinear(torch.autograd.Function):
             if not ctx.use_bias:
                 grad_bias = None
 
-        # Handle custom DDP from mcore.
-        weight.grad_added_to_main_grad = ctx.fuse_wgrad_accumulation
+        if weight.requires_grad:
+            # Handle custom DDP from mcore.
+            if ctx.fuse_wgrad_accumulation and hasattr(weight, 'grad_added_to_main_grad'):
+                weight.grad_added_to_main_grad = True
+            elif ctx.fuse_wgrad_accumulation:
+                wgrad = None
+        else:
+            wgrad = None
 
         return (
             dxmat.view(ctx.inp_shape) if ctx.requires_dgrad else None,
             dgamma,
             dbeta,
-            wgrad if weight.requires_grad else None,
+            wgrad,
             None,
             None,
             grad_bias,

transformer_engine/pytorch/module/layernorm_mlp.py

@@ -794,20 +794,34 @@ class _LayerNormMLP(torch.autograd.Function):
                 )
                 dbeta = None
 
-        # Handle custom DDP from mcore.
-        fc1_weight.grad_added_to_main_grad = ctx.fuse_wgrad_accumulation
-        fc2_weight.grad_added_to_main_grad = ctx.fuse_wgrad_accumulation
+        if fc1_weight.requires_grad:
+            # Handle custom DDP from mcore.
+            if ctx.fuse_wgrad_accumulation and hasattr(fc1_weight, 'grad_added_to_main_grad'):
+                fc1_weight.grad_added_to_main_grad = True
+            elif ctx.fuse_wgrad_accumulation:
+                fc1_wgrad = None
+        else:
+            fc1_wgrad = None
+
+        if fc2_weight.requires_grad:
+            # Handle custom DDP from mcore.
+            if ctx.fuse_wgrad_accumulation and hasattr(fc2_weight, 'grad_added_to_main_grad'):
+                fc2_weight.grad_added_to_main_grad = True
+            elif ctx.fuse_wgrad_accumulation:
+                fc2_wgrad = None
+        else:
+            fc2_wgrad = None
 
         return (
             dxmat.view(ctx.inp_shape) if ctx.requires_dgrad else None,
             dgamma,
             dbeta,
-            fc1_wgrad if fc1_weight.requires_grad else None,
+            fc1_wgrad,
             None,
             None,
             fc1_bias_grad if ctx.use_fc1_bias else None,
             None,
-            fc2_wgrad if fc2_weight.requires_grad else None,
+            fc2_wgrad,
             None,
             None,
             fc2_bias_grad if ctx.use_fc2_bias else None,

transformer_engine/pytorch/module/linear.py

@@ -415,11 +415,17 @@ class _Linear(torch.autograd.Function):
             if not ctx.use_bias:
                 grad_bias = None
 
-        # Handle custom DDP from mcore.
-        weight.grad_added_to_main_grad = ctx.fuse_wgrad_accumulation
+        if weight.requires_grad:
+            # Handle custom DDP from mcore.
+            if ctx.fuse_wgrad_accumulation and hasattr(weight, 'grad_added_to_main_grad'):
+                weight.grad_added_to_main_grad = True
+            elif ctx.fuse_wgrad_accumulation:
+                wgrad = None
+        else:
+            wgrad = None
 
         return (
-            wgrad if weight.requires_grad else None,
+            wgrad,
             None,
             None,
             dgrad.view(ctx.inp_shape) if ctx.requires_dgrad else None,