Fix cudaErrorTooManyBlocks: Grid Size Exceeded

Overview

cudaErrorTooManyBlocks occurs when launching a kernel with more blocks than the GPU supports.

Error Messages

CUDA error: too many blocks
cudaErrorTooManyBlocks

Common Causes

• •Grid dimension exceeds device limit
• •Integer overflow in grid calculation
• •Not checking device properties

Solutions

cudaDeviceProp prop;
cudaGetDeviceProperties(&prop, 0);
printf("Max grid: %d x %d x %d\n",
    prop.maxGridSize[0], prop.maxGridSize[1], prop.maxGridSize[2]);

for (int offset = 0; offset < totalBlocks; offset += maxBlocks) {
    int blocks = min(maxBlocks, totalBlocks - offset);
    kernel<<<blocks, threads>>>(data, offset);
}

Prevention Tips

• ✓Query device limits before launch
• ✓Implement work partitioning
• ✓Check for integer overflow

Code Examples

Before (Problematic)

Exceeds device limit.

kernel<<<1000000000, 256>>>();  // Way too many

After (Fixed)

Respect device limit.

int maxGrid = prop.maxGridSize[0];
int blocks = min(required, maxGrid);

Frequently Asked Questions

Related Errors

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