[Minor] Enhance JIT kernel and add dev docs (#14570)

python/sglang/jit_kernel/csrc/add_constant.cuh

@@ -0,0 +1,60 @@
+#include <sgl_kernel/tensor.h>   // For TensorMatcher, SymbolicSize, SymbolicDevice
+#include <sgl_kernel/utils.cuh>  // For LaunchKernel
+#include <sgl_kernel/utils.h>    // For div_ceil, RuntimeCheck
+
+#include <dlpack/dlpack.h>
+#include <tvm/ffi/container/tensor.h>
+
+#include <cstddef>
+#include <cstdint>
+
+namespace {
+
+template <int32_t kConstant>
+__global__ void add_constant_kernel(int32_t* dst, const int32_t* src, size_t length) {
+  size_t idx = blockIdx.x * blockDim.x + threadIdx.x;
+  if (idx < length) {
+    dst[idx] = src[idx] + kConstant;
+  }
+}
+
+constexpr size_t kBlockSize = 256;
+
+// You can also use struct with static method as an alternative
+template <int32_t kConstant>
+void add_constant(tvm::ffi::TensorView dst, tvm::ffi::TensorView src) {
+  using namespace host;
+
+  // 1. Validate input tensors
+  SymbolicSize N = {"num_elements"};
+  SymbolicDevice device_;
+  TensorMatcher({N})                  // 1D tensor, must be contiguous
+      .with_dtype<int32_t>()          // must be int32
+      .with_device<kDLCUDA>(device_)  // must be on CUDA device
+      .verify(dst)                    // check tensor dst
+      .verify(src);                   // check tensor src
+
+  // 2. Extract required parameters, prepare for kernel launch
+  const size_t num_elements = N.unwrap();
+  const size_t grid_size = div_ceil(num_elements, kBlockSize);
+  const DLDevice device = device_.unwrap();
+  [[maybe_unused]]  // optional, can be omitted
+  const size_t dynamic_smem = 0;
+  [[maybe_unused]]  // optional, LaunchKernel can auto determine stream from device
+  const cudaStream_t stream = LaunchKernel::resolve_device(device);
+  // some extra runtime checks using host::RuntimeCheck
+  RuntimeCheck(num_elements > 0, "We only support non-empty tensors, got num_elements = ", num_elements);
+
+  // 3. Launch the kernel. Error code will be automatically checked.
+  LaunchKernel(grid_size, kBlockSize, device /*, dynamic_smem*/)(
+      // kernel function
+      add_constant_kernel<kConstant>,
+      // kernel arguments
+      static_cast<int32_t*>(dst.data_ptr()),
+      static_cast<int32_t*>(src.data_ptr()),
+      num_elements);
+  // You can also manually check the last CUDA error code via:
+  // RuntimeDeviceCheck();
+}
+
+}  // namespace