ViperEkura
d0c5debbab
- Preload V into shared memory alongside K to eliminate per-element KV address lookups in the inner softmax/accum loop (doubles smem) - Cache split-KV partial tensors (o_part, ml_part) with static tensors instead of per-call allocation in both decode and paged-decode paths - Force is_causal=True in CUDA decode backend (decode is always causal)
57 lines
2.0 KiB
Plaintext
57 lines
2.0 KiB
Plaintext
#include "attn_dispatchers.cuh"
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#include "attn_entry_utils.cuh"
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torch::Tensor attn_paged_decode(
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torch::Tensor q,
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torch::Tensor k_cache,
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torch::Tensor v_cache,
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torch::Tensor req_to_token,
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torch::Tensor req_pool_indices,
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torch::Tensor kv_indptr,
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int64_t max_seq_len,
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c10::optional<torch::Tensor> mask,
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int64_t causal_offset,
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double scale
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) {
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const at::cuda::OptionalCUDAGuard device_guard(device_of(q));
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auto stream = at::cuda::getCurrentCUDAStream();
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AttentionParams<bf16> p;
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attn_pack_paged_decode_params(q, k_cache, v_cache,
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req_to_token, req_pool_indices, kv_indptr,
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max_seq_len, mask, causal_offset, scale, p);
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auto O = torch::empty({q.size(0), q.size(1), q.size(2)}, q.options());
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p.o = (bf16*)O.data_ptr();
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{
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static torch::Tensor s_o_part, s_ml_part;
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int64_t o_needed = (int64_t)p.batch * p.q_head * MAX_SPLITS * p.head_dim;
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auto fopt = torch::TensorOptions().dtype(torch::kFloat32).device(torch::kCUDA);
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if (!s_o_part.defined() || s_o_part.numel() < o_needed) {
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s_o_part = torch::empty({p.batch, p.q_head, MAX_SPLITS, p.head_dim}, fopt);
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s_ml_part = torch::empty({p.batch, p.q_head, MAX_SPLITS, 2}, fopt);
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}
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p.o_part = (float*)s_o_part.data_ptr();
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p.ml_part = (float*)s_ml_part.data_ptr();
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}
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DISPATCH_HEAD_DIM(p.head_dim, dispatch_paged_decode, p, stream);
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C10_CUDA_CHECK(cudaGetLastError());
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return O;
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}
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PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
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m.def("attn_paged_decode", &attn_paged_decode,
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py::arg("q"),
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py::arg("k_cache"),
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py::arg("v_cache"),
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py::arg("req_to_token"),
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py::arg("req_pool_indices"),
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py::arg("kv_indptr"),
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py::arg("max_seq_len"),
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py::arg("mask") = py::none(),
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py::arg("causal_offset") = -1,
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py::arg("scale") = 0.0,
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"SGLang-style paged decode: flat KV pool + req_to_token + kv_indptr.");
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}
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