[WIP] Added sgDMA operator for scatter kvcache communication.

csrc/sgdma_kernel.cu

@@ -0,0 +1,59 @@
+#include <cuda_runtime.h>
+#include <stdexcept>
+#include <string>
+
+// CUDA error checking macro
+#define CUDA_CHECK(call) do { \
+    cudaError_t err = call; \
+    if (err != cudaSuccess) { \
+        throw std::runtime_error(std::string("CUDA Error: ") + cudaGetErrorString(err)); \
+    } \
+} while (0)
+
+/**
+ * Synchronous 2D memory copy using cudaMemcpy2D.
+ *
+ * @param dst Destination pointer
+ * @param dpitch Destination pitch (bytes) - stride between rows in destination
+ * @param src Source pointer
+ * @param spitch Source pitch (bytes) - stride between rows in source
+ * @param width Width of data to copy per row (bytes)
+ * @param height Number of rows to copy
+ * @param kind Transfer direction (cudaMemcpyHostToDevice, cudaMemcpyDeviceToHost, etc.)
+ */
+void cuda_memcpy_2d(
+    void* dst,
+    size_t dpitch,
+    const void* src,
+    size_t spitch,
+    size_t width,
+    size_t height,
+    cudaMemcpyKind kind
+) {
+    CUDA_CHECK(cudaMemcpy2D(dst, dpitch, src, spitch, width, height, kind));
+}
+
+/**
+ * Asynchronous 2D memory copy using cudaMemcpy2DAsync.
+ *
+ * @param dst Destination pointer
+ * @param dpitch Destination pitch (bytes) - stride between rows in destination
+ * @param src Source pointer
+ * @param spitch Source pitch (bytes) - stride between rows in source
+ * @param width Width of data to copy per row (bytes)
+ * @param height Number of rows to copy
+ * @param kind Transfer direction
+ * @param stream CUDA stream for asynchronous execution
+ */
+void cuda_memcpy_2d_async(
+    void* dst,
+    size_t dpitch,
+    const void* src,
+    size_t spitch,
+    size_t width,
+    size_t height,
+    cudaMemcpyKind kind,
+    cudaStream_t stream
+) {
+    CUDA_CHECK(cudaMemcpy2DAsync(dst, dpitch, src, spitch, width, height, kind, stream));
+}