Fix cudaErrorCooperativeLaunchTooLarge: Grid Too Large for Coop Kernel

Overview

cudaErrorCooperativeLaunchTooLarge occurs when launching a cooperative kernel with more blocks than the GPU can run concurrently.

Error Messages

CUDA error: cooperative launch too large
cudaErrorCooperativeLaunchTooLarge

Common Causes

• •Grid size exceeds device occupancy
• •Not checking max cooperative blocks
• •Using grid_group::sync() with too many blocks

Solutions

int numBlocks;
cudaOccupancyMaxActiveBlocksPerMultiprocessor(&numBlocks, kernel, blockSize, 0);
int deviceNumSMs;
cudaDeviceGetAttribute(&deviceNumSMs, cudaDevAttrMultiProcessorCount, 0);
int maxCoopBlocks = numBlocks * deviceNumSMs;

cudaLaunchCooperativeKernel((void*)kernel, maxCoopBlocks, blockSize, args);

Prevention Tips

• ✓Query occupancy before cooperative launch
• ✓Cooperative kernels limited to concurrent blocks
• ✓Use regular kernels if grid sync not needed

Code Examples

Before (Problematic)

Too many blocks for cooperative launch.

cudaLaunchCooperativeKernel(kernel, 10000, 256, args);

After (Fixed)

Query and respect limit.

int maxBlocks = getMaxCooperativeBlocks(kernel, 256);
cudaLaunchCooperativeKernel(kernel, maxBlocks, 256, args);

Frequently Asked Questions

Related Errors

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