FSDP grad fusion support (#2191)

* FSDP grad fusion support
Signed-off-by: Selvaraj Anandaraj <selvaraja@login-ptyche01.ptyche.clusters.nvidia.com>

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* Re-factored grad overwriting usage
Signed-off-by: Selvaraj Anandaraj <selvaraja@login-ptyche02.ptyche.clusters.nvidia.com>

* Update transformer_engine/pytorch/ops/basic/basic_linear.py
Co-authored-by: Tim Moon <4406448+timmoon10@users.noreply.github.com>
Signed-off-by: Selvaraj Anandaraj <selvaraja@nvidia.com>

* Update transformer_engine/pytorch/ops/fused/backward_linear_add.py
Co-authored-by: Tim Moon <4406448+timmoon10@users.noreply.github.com>
Signed-off-by: Selvaraj Anandaraj <selvaraja@nvidia.com>

* Update transformer_engine/pytorch/ops/fused/backward_linear_scale.py
Co-authored-by: Tim Moon <4406448+timmoon10@users.noreply.github.com>
Signed-off-by: Selvaraj Anandaraj <selvaraja@nvidia.com>

* Update transformer_engine/pytorch/ops/fused/userbuffers_backward_linear.py
Co-authored-by: Tim Moon <4406448+timmoon10@users.noreply.github.com>
Signed-off-by: Selvaraj Anandaraj <selvaraja@nvidia.com>

* Modified API usage, added arg details
Signed-off-by: Selvaraj Anandaraj <selvaraja@login-ptyche02.ptyche.clusters.nvidia.com>

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---------
Signed-off-by: Selvaraj Anandaraj <selvaraja@login-ptyche01.ptyche.clusters.nvidia.com>
Signed-off-by: Selvaraj Anandaraj <selvaraja@login-ptyche02.ptyche.clusters.nvidia.com>
Signed-off-by: Selvaraj Anandaraj <selvaraja@nvidia.com>
Co-authored-by: Selvaraj Anandaraj <selvaraja@login-ptyche01.ptyche.clusters.nvidia.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Selvaraj Anandaraj <selvaraja@login-ptyche02.ptyche.clusters.nvidia.com>
Co-authored-by: Tim Moon <4406448+timmoon10@users.noreply.github.com>

transformer_engine/pytorch/module/grouped_linear.py

@@ -402,7 +402,11 @@ class _GroupedLinear(torch.autograd.Function):
                     use_bias=ctx.use_bias if grad_biases[0] is None else None,
                     bias=biases,
                     use_split_accumulator=wgrad_gemm_use_split_accumulator,
-                    accumulate=accumulate_wgrad_into_param_main_grad,
+                    accumulate=(
+                        accumulate_wgrad_into_param_main_grad
+                        if not getattr(weights[0], "overwrite_main_grad", False)
+                        else False
+                    ),
                 )
                 # WGRAD
                 if ctx.wgrad_store is not None and ctx.wgrad_store.delay_wgrad_compute():
@@ -519,7 +523,9 @@ class GroupedLinear(TransformerEngineBaseModule):
                              the weight gradient. When enabled, it is assumed that the weights
                              have an additional `main_grad` attribute (used instead of the
                              regular `grad`) which is a pre-allocated buffer of the correct
-                             size to accumulate gradients in.
+                             size to accumulate gradients in. This argument along with
+                             weight tensor having attribute 'overwrite_main_grad' set to True
+                             will overwrite `main_grad` instead of accumulating.
     return_bias : bool, default = `False`
                  when set to `True`, this module will not apply the additive bias itself, but
                  instead return the bias value during the forward pass together with the

transformer_engine/pytorch/module/layernorm_linear.py

@@ -849,7 +849,11 @@ class _LayerNormLinear(torch.autograd.Function):
                         main_grad.dtype if ctx.fuse_wgrad_accumulation else ctx.activation_dtype
                     ),
                     "quantization_params": ctx.grad_weight_quantizer,
-                    "accumulate": accumulate_wgrad_into_param_main_grad,
+                    "accumulate": (
+                        accumulate_wgrad_into_param_main_grad
+                        if not getattr(weight, "overwrite_main_grad", False)
+                        else False
+                    ),
                     "layout": "NT",
                     "out": main_grad if ctx.fuse_wgrad_accumulation else None,
                     "bias": (bias if (grad_bias is None and not ctx.fp8) else None),
@@ -1125,7 +1129,9 @@ class LayerNormLinear(TransformerEngineBaseModule):
                              the weight gradient. When enabled, it is assumed that the weights
                              have an additional `main_grad` attribute (used instead of the
                              regular `grad`) which is a pre-allocated buffer of the correct
-                             size to accumulate gradients in.
+                             size to accumulate gradients in. This argument along with
+                             weight tensor having attribute 'overwrite_main_grad' set to True
+                             will overwrite `main_grad` instead of accumulating.
     return_bias : bool, default = `False`
                  when set to `True`, this module will not apply the additive bias itself, but
                  instead return the bias value during the forward pass together with the

transformer_engine/pytorch/module/layernorm_mlp.py

@@ -948,7 +948,11 @@ class _LayerNormMLP(torch.autograd.Function):
                         else ctx.activation_dtype
                     ),
                     "quantization_params": ctx.fc2_grad_weight_quantizer,  # wgrad in high precision
-                    "accumulate": accumulate_wgrad_into_param_main_grad,
+                    "accumulate": (
+                        accumulate_wgrad_into_param_main_grad
+                        if not getattr(fc1_weight, "overwrite_main_grad", False)
+                        else False
+                    ),
                     "layout": "NT",
                     "out": origin_fc2_weight.main_grad if ctx.fuse_wgrad_accumulation else None,
                     "bias": fc2_bias if fc2_bias is not None and fc2_bias_grad is None else None,
@@ -1189,7 +1193,11 @@ class _LayerNormMLP(torch.autograd.Function):
                         else ctx.activation_dtype
                     ),
                     "quantization_params": ctx.fc1_grad_weight_quantizer,
-                    "accumulate": accumulate_wgrad_into_param_main_grad,
+                    "accumulate": (
+                        accumulate_wgrad_into_param_main_grad
+                        if not getattr(fc2_weight, "overwrite_main_grad", False)
+                        else False
+                    ),
                     "layout": "NT",
                     "out": origin_fc1_weight.main_grad if ctx.fuse_wgrad_accumulation else None,
                     "bias": fc1_bias if fuse_gemm_and_bias_fc1_wgrad else None,
@@ -1484,7 +1492,9 @@ class LayerNormMLP(TransformerEngineBaseModule):
                              the weight gradient. When enabled, it is assumed that the weights
                              have an additional `main_grad` attribute (used instead of the
                              regular `grad`) which is a pre-allocated buffer of the correct
-                             size to accumulate gradients in.
+                             size to accumulate gradients in. This argument along with
+                             weight tensor having attribute 'overwrite_main_grad' set to True
+                             will overwrite `main_grad` instead of accumulating.
     return_bias : bool, default = `False`
                  when set to `True`, this module will not apply the additive bias for FC2, but
                  instead return the bias value during the forward pass together with the

transformer_engine/pytorch/module/linear.py

@@ -843,7 +843,11 @@ class _Linear(torch.autograd.Function):
                         main_grad.dtype if ctx.fuse_wgrad_accumulation else ctx.activation_dtype
                     ),
                     "quantization_params": ctx.grad_weight_quantizer,
-                    "accumulate": accumulate_wgrad_into_param_main_grad,
+                    "accumulate": (
+                        accumulate_wgrad_into_param_main_grad
+                        if not getattr(weight, "overwrite_main_grad", False)
+                        else False
+                    ),
                     "layout": "NT",
                     "out": main_grad if ctx.fuse_wgrad_accumulation else None,
                     "bias": (bias if (grad_bias is None and not ctx.fp8) else None),
@@ -1061,7 +1065,9 @@ class Linear(TransformerEngineBaseModule):
                              the weight gradient. When enabled, it is assumed that the weights
                              have an additional `main_grad` attribute (used instead of the
                              regular `grad`) which is a pre-allocated buffer of the correct
-                             size to accumulate gradients in.
+                             size to accumulate gradients in. This argument along with
+                             weight tensor having attribute 'overwrite_main_grad' set to True
+                             will overwrite `main_grad` instead of accumulating.
     return_bias : bool, default = `False`
                  when set to `True`, this module will not apply the additive bias itself, but
                  instead return the bias value during the forward pass together with the

transformer_engine/pytorch/ops/basic/basic_linear.py

@@ -80,7 +80,9 @@ class BasicLinear(BasicOperation):
         autograd. The weight's `main_grad` must be set externally and
         there is no guarantee that `grad` will be set or be
         meaningful. This is primarily intented to integrate with
-        Megatron-LM.
+        Megatron-LM. This argument along with weight tensor having
+        attribute 'overwrite_main_grad' set to True will overwrite
+        `main_grad` instead of accumulating.
     userbuffers_options, dict, optional
         Options for overlapping tensor-parallel communication with
         compute using Userbuffers. This feature is highly
@@ -1019,6 +1021,7 @@ class BasicLinear(BasicOperation):
             weight_param = self.weight
             if hasattr(weight_param, "__fsdp_param__"):
                 weight_param.main_grad = weight_param.get_main_grad()
+            accumulate_into_main_grad = not getattr(weight_param, "overwrite_main_grad", False)
             if not hasattr(weight_param, "main_grad"):
                 raise RuntimeError(
                     "BasicLinear op is configured with "

transformer_engine/pytorch/ops/fused/backward_linear_add.py

@@ -59,6 +59,7 @@ class BackwardLinearAdd(FusedOperation):
             weight_param = linear_op.weight
             if hasattr(weight_param, "__fsdp_param__"):
                 weight_param.main_grad = weight_param.get_main_grad()
+            accumulate_into_main_grad = not getattr(weight_param, "overwrite_main_grad", False)
             if not hasattr(weight_param, "main_grad"):
                 raise RuntimeError(
                     "BasicLinear op is configured with "

transformer_engine/pytorch/ops/fused/backward_linear_scale.py

@@ -60,6 +60,7 @@ class BackwardLinearScale(FusedOperation):
             weight_param = linear_op.weight
             if hasattr(weight_param, "__fsdp_param__"):
                 weight_param.main_grad = weight_param.get_main_grad()
+            accumulate_into_main_grad = not getattr(weight_param, "overwrite_main_grad", False)
             if not hasattr(weight_param, "main_grad"):
                 raise RuntimeError(
                     "BasicLinear op is configured with "

transformer_engine/pytorch/ops/fused/userbuffers_backward_linear.py

@@ -523,6 +523,7 @@ class UserbuffersBackwardLinear(FusedOperation):
             weight_param = linear_op.weight
             if hasattr(weight_param, "__fsdp_param__"):
                 weight_param.main_grad = weight_param.get_main_grad()
+            accumulate_into_main_grad = not getattr(weight_param, "overwrite_main_grad", False)
             if not hasattr(weight_param, "main_grad"):
                 raise RuntimeError(
                     "BasicLinear op is configured with "