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cudaErrorMisalignedAddress (716)cudaErrorMisalignedAddress (error code 716) occurs when a memory operation accesses data at an address that doesn't meet CUDA's alignment requirements. GPUs require specific memory alignment for efficient access, and violating these requirements can cause errors or severe performance degradation. This error is particularly common when working with custom data structures, texture memory, or when casting pointers to different types. Modern GPUs are somewhat tolerant of misalignment, but certain operations still require strict alignment. This guide covers memory alignment requirements, how to diagnose alignment issues, and best practices for ensuring properly aligned memory accesses in CUDA.
CUDA error: misaligned address cudaErrorMisalignedAddress: misaligned address RuntimeError: CUDA error: misaligned address Error: Misaligned address in texture fetch
CUDA allocations are aligned by default, but verify for custom allocations.
// cudaMalloc is aligned to 256 bytes by default
float* d_data;
cudaMalloc(&d_data, 1024 * sizeof(float)); // Automatically aligned
// For host memory, use aligned allocation
#include <cstdlib>
float* h_data;
posix_memalign((void**)&h_data, 256, 1024 * sizeof(float));
// Or use cudaMallocHost for pinned memory (always aligned)
cudaMallocHost(&h_data, 1024 * sizeof(float));
// Check alignment
if ((uintptr_t)d_data % 256 == 0) {
printf("Properly aligned to 256 bytes\n");
}Add alignment attributes to structures used in device code.
// Without alignment (may cause issues)
struct BadData {
char flag; // 1 byte
double value; // 8 bytes - may be misaligned!
int count; // 4 bytes
};
// With proper alignment
struct __align__(16) GoodData {
char flag;
double value;
int count;
};
// Or use individual alignment
struct AlignedData {
char flag;
__align__(8) double value; // Explicitly align to 8 bytes
int count;
};
// Verify structure size and alignment
printf("Size: %zu, Alignment: %zu\n",
sizeof(GoodData), alignof(GoodData));Ensure pointer arithmetic maintains proper alignment.
float* d_data;
cudaMalloc(&d_data, 1024 * sizeof(float));
// Wrong: byte-level offset may misalign
char* byte_ptr = (char*)d_data;
float* misaligned = (float*)(byte_ptr + 13); // 13 bytes - misaligned!
// Correct: offset in multiples of element size
float* aligned = d_data + 13; // 13 * sizeof(float) - stays aligned
// For general offsets, round to alignment
size_t offset = 13;
size_t aligned_offset = (offset + 3) & ~3; // Round up to multiple of 4
float* properly_aligned = (float*)((char*)d_data + aligned_offset * sizeof(float));Texture memory has specific alignment requirements.
// Allocate with proper alignment for textures
cudaChannelFormatDesc channelDesc = cudaCreateChannelDesc<float>();
cudaArray* cuArray;
// Specify alignment requirements
cudaMallocArray(&cuArray, &channelDesc, width, height);
// For linear memory textures
size_t offset;
cudaBindTexture(&offset, texRef, d_data, &channelDesc, size);
if (offset != 0) {
printf("Warning: Texture binding offset: %zu\n", offset);
// Reallocate with proper alignment if needed
}
// Texture objects (CUDA 5.0+) handle alignment automatically
cudaTextureObject_t texObj;
cudaResourceDesc resDesc = {};
resDesc.resType = cudaResourceTypeLinear;
resDesc.res.linear.devPtr = d_data;
resDesc.res.linear.sizeInBytes = size;
resDesc.res.linear.desc = channelDesc;
cudaCreateTextureObject(&texObj, &resDesc, &texDesc, NULL);For performance-critical code, use vector types and aligned loads.
// Use vector types for automatic alignment
__global__ void alignedKernel(float4* data) {
int idx = blockIdx.x * blockDim.x + threadIdx.x;
// float4 is 16-byte aligned
float4 val = data[idx]; // Coalesced, aligned access
val.x *= 2.0f;
val.y *= 2.0f;
val.z *= 2.0f;
val.w *= 2.0f;
data[idx] = val;
}
// Ensure allocation matches
float4* d_data;
cudaMalloc(&d_data, n * sizeof(float4));
// Or use explicit aligned loads
__global__ void explicitAlignedKernel(float* data) {
int idx = blockIdx.x * blockDim.x + threadIdx.x;
// Load 4 floats at once (16 bytes) - requires alignment
float4* aligned_ptr = (float4*)&data[idx * 4];
float4 val = *aligned_ptr;
}Enable compiler warnings and use static assertions.
// Static assertion for alignment
template<typename T>
__host__ __device__ void checkAlignment(T* ptr) {
static_assert(alignof(T) <= 256, "Type requires > 256 byte alignment");
// Runtime check
assert((uintptr_t)ptr % alignof(T) == 0);
}
// Compile-time checks for structures
struct MyData {
double x;
int y;
};
static_assert(sizeof(MyData) % 8 == 0, "MyData size not aligned");
// Use compiler flags to detect alignment issues
// nvcc -Xcompiler -Wall -Wcast-align kernel.cuStructure has no alignment, causing the double field to be misaligned. This can cause errors or performance degradation.
struct UnalignedData {
char flag;
double value; // Likely at offset 1, not aligned to 8!
int count;
};
__global__ void badKernel(UnalignedData* data) {
int idx = threadIdx.x;
// Accessing misaligned double may error or be slow
data[idx].value *= 2.0;
}
int main() {
UnalignedData* d_data;
cudaMalloc(&d_data, 256 * sizeof(UnalignedData));
badKernel<<<1, 256>>>(d_data); // May cause alignment errors
return 0;
}Structure uses __align__(16) attribute ensuring proper alignment. Compiler adds necessary padding, and all memory accesses are aligned.
struct __align__(16) AlignedData {
char flag;
double value; // Compiler adds padding to align to 8 bytes
int count;
};
__global__ void goodKernel(AlignedData* data) {
int idx = threadIdx.x;
// All accesses properly aligned
data[idx].value *= 2.0;
}
int main() {
AlignedData* d_data;
cudaMalloc(&d_data, 256 * sizeof(AlignedData));
// Verify alignment
assert((uintptr_t)d_data % 16 == 0);
goodKernel<<<1, 256>>>(d_data);
cudaDeviceSynchronize();
cudaFree(d_data);
return 0;
}cudaMalloc guarantees alignment to at least 256 bytes, which satisfies the requirements for all standard data types and most operations. This is more than sufficient for typical use cases.
Modern GPUs (compute capability 2.0+) can handle some misaligned accesses, but with performance penalties. Certain operations like texture fetches and atomic operations still require proper alignment. Always align for best performance.
Use sizeof() and alignof() operators: printf("Size: %zu, Align: %zu\n", sizeof(MyStruct), alignof(MyStruct)). Use static_assert to enforce alignment at compile time.
Alignment refers to the starting address of data (e.g., must be multiple of 16). Coalescing refers to memory access patterns where threads in a warp access contiguous memory. Both are important for performance but address different issues.
Invalid memory accesses including misalignment
Invalid parameters including alignment
Kernel failures from memory errors
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