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cudaErrorInvalidConfiguration (9)cudaErrorInvalidConfiguration (error code 9) occurs when the kernel launch configuration violates hardware constraints. This includes block sizes exceeding 1024 threads, grid dimensions exceeding limits, or requesting too much shared memory. Every CUDA device has limits on thread organization and resources. These limits vary by compute capability. Understanding and respecting these constraints is essential for correct kernel launches. This guide covers launch configuration constraints and how to validate configurations before launch.
CUDA error: invalid configuration argument cudaErrorInvalidConfiguration: invalid configuration argument CUDA_ERROR_INVALID_CONFIGURATION too many threads per block shared memory size exceeds limit
Query device for actual configuration limits.
cudaDeviceProp prop;
cudaGetDeviceProperties(&prop, 0);
printf("Max threads per block: %d\n", prop.maxThreadsPerBlock);
printf("Max block dim: (%d, %d, %d)\n",
prop.maxThreadsDim[0], prop.maxThreadsDim[1], prop.maxThreadsDim[2]);
printf("Max grid dim: (%d, %d, %d)\n",
prop.maxGridSize[0], prop.maxGridSize[1], prop.maxGridSize[2]);
printf("Shared memory per block: %zu bytes\n", prop.sharedMemPerBlock);
printf("Registers per block: %d\n", prop.regsPerBlock);Ensure block size respects all constraints.
// Common limits (varies by compute capability):
// - Total threads per block: 1024 max
// - blockDim.x: 1024 max
// - blockDim.y: 1024 max
// - blockDim.z: 64 max
// - blockDim.x * blockDim.y * blockDim.z <= 1024
// BAD: Exceeds limit
dim3 block(32, 32, 2); // 32*32*2 = 2048 > 1024!
// GOOD: Respects limit
dim3 block(16, 16, 2); // 16*16*2 = 512 <= 1024
// Validation function
bool validateBlockDim(dim3 block, cudaDeviceProp& prop) {
if (block.x > prop.maxThreadsDim[0]) return false;
if (block.y > prop.maxThreadsDim[1]) return false;
if (block.z > prop.maxThreadsDim[2]) return false;
if (block.x * block.y * block.z > prop.maxThreadsPerBlock) return false;
return true;
}Request appropriate shared memory amount.
// Check available shared memory
cudaDeviceProp prop;
cudaGetDeviceProperties(&prop, 0);
size_t maxShared = prop.sharedMemPerBlock; // e.g., 49152 bytes
// Dynamic shared memory in kernel launch
extern __shared__ float s[];
// Launch with dynamic shared memory
size_t sharedMemSize = 1024 * sizeof(float);
if (sharedMemSize > maxShared) {
printf("Requested %zu bytes, max is %zu\n", sharedMemSize, maxShared);
return;
}
kernel<<<grid, block, sharedMemSize>>>(data);Ensure grid and block have non-zero dimensions.
// Calculate grid size safely
int n = getDataSize();
if (n <= 0) {
printf("No data to process\n");
return;
}
int threadsPerBlock = 256;
// Use ceiling division, but check for zero
int blocksPerGrid = (n + threadsPerBlock - 1) / threadsPerBlock;
if (blocksPerGrid == 0) blocksPerGrid = 1;
printf("Launching %d blocks of %d threads\n", blocksPerGrid, threadsPerBlock);
kernel<<<blocksPerGrid, threadsPerBlock>>>(data, n);Get limits for a specific kernel based on its register usage.
// Get occupancy info for kernel
int blockSize = 256;
int minGridSize;
int optimalBlockSize;
cudaOccupancyMaxPotentialBlockSize(&minGridSize, &optimalBlockSize, kernel, 0, 0);
printf("Optimal block size: %d\n", optimalBlockSize);
// Get max active blocks
int maxActiveBlocks;
cudaOccupancyMaxActiveBlocksPerMultiprocessor(&maxActiveBlocks, kernel, blockSize, 0);
printf("Max active blocks per SM: %d\n", maxActiveBlocks);Block size of 4096 exceeds 1024 thread limit.
// Arbitrary 2D block - may exceed limits
dim3 block(64, 64); // 64*64 = 4096 > 1024!
dim3 grid(n/64, m/64);
kernel<<<grid, block>>>(data);Uses validated block size and checks grid dimensions.
// Safe 2D configuration with validation
cudaDeviceProp prop;
cudaGetDeviceProperties(&prop, 0);
dim3 block(32, 32); // 32*32 = 1024, exactly at limit
// Or calculate optimal
int optBlockSize;
cudaOccupancyMaxPotentialBlockSize(nullptr, &optBlockSize, kernel, 0, 0);
int sqrtBlock = (int)sqrt(optBlockSize);
dim3 safeBlock(sqrtBlock, sqrtBlock);
dim3 grid((n + block.x - 1) / block.x, (m + block.y - 1) / block.y);
if (grid.x > 0 && grid.y > 0) {
kernel<<<grid, safeBlock>>>(data);
}1024 threads per block on all modern GPUs (compute capability 2.0+). This is the product of blockDim.x * blockDim.y * blockDim.z.
32*32=1024 is exactly at the limit. 33*33=1089 exceeds 1024 threads per block. Even one extra thread causes failure.
Query cudaDeviceProp at runtime and adjust configuration. Use cudaOccupancyMaxPotentialBlockSize for automatic optimal configuration.
Config errors cause launch failures
Invalid configuration is a type of invalid value
Shared memory requests can fail
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