Skip to content

CUDA: fix misaligned synchronization in FA #13469

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
May 12, 2025
Merged

CUDA: fix misaligned synchronization in FA #13469

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
5 changes: 5 additions & 0 deletions ggml/src/ggml-cuda/fattn-mma-f16.cuh
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -895,6 +895,11 @@ static __device__ __forceinline__ void flash_attn_ext_f16_process_tile(
float2 * dstk_fixup_meta = dstk_fixup + (gridDim.x + blockIdx.x)*ncols;
dstk_fixup_meta[(threadIdx.y/np)*cols_per_warp + threadIdx.x] = make_float2(KQ_cmn, KQ_crs);
}
} else if (np > 1) {
// Warps with threadIdx.y % np == 0 execute a __syncthreads() in the if branch.
// Therefore, all other warps also need to execute a __syncthreads().
// Otherwise the points at which warps synchronize with each other would become misaligned.
__syncthreads();
}

#pragma unroll
Expand Down
Loading