[Feat] Enable PDL automatically on Hopper architecture (#5981)

sgl-kernel/python/sgl_kernel/elementwise.py

 from typing import Optional
 
 import torch
-from sgl_kernel.utils import get_cuda_stream
+from sgl_kernel.utils import get_cuda_stream, is_hopper_arch
 
 
 # These implementations extensively draw from and build upon the FlashInfer project https://github.com/flashinfer-ai/flashinfer
@@ -11,7 +11,7 @@ def rmsnorm(
     weight: torch.Tensor,
     eps: float = 1e-6,
     out: Optional[torch.Tensor] = None,
-    enable_pdl: bool = False,
+    enable_pdl: Optional[bool] = None,
 ) -> torch.Tensor:
     r"""Root mean square normalization.
 
@@ -27,9 +27,10 @@ def rmsnorm(
         Epsilon for numerical stability.
     out: Optional[torch.Tensor]
         The output tensor, if specified, the kernel will update this tensor inplace.
-    enable_pdl: bool
+    enable_pdl: Optional[bool]
         Whether to enable `programmatic dependent launch
         <https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#programmatic-dependent-launch-and-synchronization>`_
+        If None, will be automatically enabled on Hopper architecture.
 
     Returns
     -------
@@ -38,6 +39,8 @@ def rmsnorm(
     """
     if out is None:
         out = torch.empty_like(input)
+    if enable_pdl is None:
+        enable_pdl = is_hopper_arch()
     torch.ops.sgl_kernel.rmsnorm.default(out, input, weight, eps, enable_pdl)
     return out
 
@@ -47,7 +50,7 @@ def fused_add_rmsnorm(
     residual: torch.Tensor,
     weight: torch.Tensor,
     eps: float = 1e-6,
-    enable_pdl: bool = False,
+    enable_pdl: Optional[bool] = None,
 ) -> None:
     r"""Fused add root mean square normalization.
 
@@ -67,10 +70,13 @@ def fused_add_rmsnorm(
         Weight tensor, shape (hidden_size,).
     eps: float
         Epsilon for numerical stability.
-    enable_pdl: bool
+    enable_pdl: Optional[bool]
         Whether to enable `programmatic dependent launch
         <https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#programmatic-dependent-launch-and-synchronization>`_
+        If None, will be automatically enabled on Hopper architecture.
     """
+    if enable_pdl is None:
+        enable_pdl = is_hopper_arch()
     torch.ops.sgl_kernel.fused_add_rmsnorm.default(
         input, residual, weight, eps, enable_pdl
     )
@@ -81,7 +87,7 @@ def gemma_rmsnorm(
     weight: torch.Tensor,
     eps: float = 1e-6,
     out: Optional[torch.Tensor] = None,
-    enable_pdl: bool = False,
+    enable_pdl: Optional[bool] = None,
 ) -> torch.Tensor:
     r"""Gemma-style root mean square normalization.
 
@@ -97,9 +103,10 @@ def gemma_rmsnorm(
         Epsilon for numerical stability.
     out: Optional[torch.Tensor]
         The output tensor, if specified, the kernel will update this tensor inplace.
-    enable_pdl: bool
+    enable_pdl: Optional[bool]
         Whether to enable `programmatic dependent launch
         <https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#programmatic-dependent-launch-and-synchronization>`_
+        If None, will be automatically enabled on Hopper architecture.
 
     Returns
     -------
@@ -108,6 +115,8 @@ def gemma_rmsnorm(
     """
     if out is None:
         out = torch.empty_like(input)
+    if enable_pdl is None:
+        enable_pdl = is_hopper_arch()
     torch.ops.sgl_kernel.gemma_rmsnorm.default(out, input, weight, eps, enable_pdl)
     return out
 
@@ -117,7 +126,7 @@ def gemma_fused_add_rmsnorm(
     residual: torch.Tensor,
     weight: torch.Tensor,
     eps: float = 1e-6,
-    enable_pdl: bool = False,
+    enable_pdl: Optional[bool] = None,
 ) -> None:
     r"""Gemma-style fused add root mean square normalization.
 
@@ -137,10 +146,13 @@ def gemma_fused_add_rmsnorm(
         Weight tensor, shape (hidden_size,).
     eps: float
         Epsilon for numerical stability.
-    enable_pdl: bool
+    enable_pdl: Optional[bool]
         Whether to enable `programmatic dependent launch
         <https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#programmatic-dependent-launch-and-synchronization>`_
+        If None, will be automatically enabled on Hopper architecture.
     """
+    if enable_pdl is None:
+        enable_pdl = is_hopper_arch()
     torch.ops.sgl_kernel.gemma_fused_add_rmsnorm.default(
         input, residual, weight, eps, enable_pdl
     )

sgl-kernel/python/sgl_kernel/utils.py

@@ -39,3 +39,10 @@ def _to_tensor_scalar_tuple(x):
         return (x, 0)
     else:
         return (None, x)
+
+
+def is_hopper_arch() -> bool:
+    # Hopper arch's compute capability == 9.0
+    device = torch.cuda.current_device()
+    major, minor = torch.cuda.get_device_capability(device)
+    return major == 9