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Update the initialization of dk/dv_semaphore #1839

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Merged
tridao merged 1 commit into from
Aug 25, 2025
Merged

Update the initialization of dk/dv_semaphore #1839

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6 changes: 3 additions & 3 deletions hopper/flash_api.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1529,9 +1529,9 @@ std::tuple<at::Tensor, at::Tensor, at::Tensor, at::Tensor, at::Tensor, at::Tenso
at::Tensor dq_semaphore = torch::empty({(seqlen_q + kBlockM - 1) / kBlockM, batch_size, num_heads}, opts.dtype(torch::kInt32));
params.dq_semaphore = dq_semaphore.data_ptr<int>();
if (num_heads_k != num_heads && params.deterministic) {
// TODO: do we need to zero them out?
at::Tensor dk_semaphore = torch::empty({(seqlen_k + kBlockN - 1) / kBlockN, batch_size, num_heads_k}, opts.dtype(torch::kInt32));
at::Tensor dv_semaphore = torch::empty({(seqlen_k + kBlockN - 1) / kBlockN, batch_size, num_heads_k}, opts.dtype(torch::kInt32));
// TODO: maybe also zero'ed out dk_semaphore and dv_semaphore in the backward preprocess kernel
at::Tensor dk_semaphore = torch::zeros({(seqlen_k + kBlockN - 1) / kBlockN, batch_size, num_heads_k}, opts.dtype(torch::kInt32));
at::Tensor dv_semaphore = torch::zeros({(seqlen_k + kBlockN - 1) / kBlockN, batch_size, num_heads_k}, opts.dtype(torch::kInt32));
params.dk_semaphore = dk_semaphore.data_ptr<int>();
params.dv_semaphore = dv_semaphore.data_ptr<int>();
}
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