issue/1065 - introduce mha kvcache

include/infinicore/ops/mha_kvcache.hpp

@@ -0,0 +1,51 @@
+#pragma once
+
+#include "../device.hpp"
+#include "../graph/graph.hpp"
+#include "common/op.hpp"
+#include <optional>
+
+namespace infinicore::op {
+
+// Flash Attention KV-cache decode op.
+//
+// Wraps flash::mha_fwd_kvcache for single-step (decode) attention over a
+// paged KV cache.
+//
+// Tensor shapes:
+//   out         : [batch_size, seqlen_q, num_heads, head_size]
+//   q           : [batch_size, seqlen_q, num_heads, head_size]
+//   k_cache     : [num_blocks, block_size, num_heads_k, head_size]   (paged layout)
+//   v_cache     : [num_blocks, block_size, num_heads_k, head_size]   (paged layout)
+//   seqlens_k   : [batch_size]   int32 — total KV length per request
+//   block_table : [batch_size, max_num_blocks_per_seq]  int32
+
+INFINICORE_GRAPH_OP_CLASS(
+    MhaKVCache,
+    Tensor,           // out
+    const Tensor &,   // q
+    const Tensor &,   // k_cache
+    const Tensor &,   // v_cache
+    const Tensor &,   // seqlens_k
+    const Tensor &,   // block_table
+    std::optional<Tensor>,  // alibi_slopes
+    float);           // scale
+
+Tensor mha_kvcache(const Tensor &q,
+                   const Tensor &k_cache,
+                   const Tensor &v_cache,
+                   const Tensor &seqlens_k,
+                   const Tensor &block_table,
+                   std::optional<Tensor> alibi_slopes,
+                   float scale);
+
+void mha_kvcache_(Tensor out,
+                  const Tensor &q,
+                  const Tensor &k_cache,
+                  const Tensor &v_cache,
+                  const Tensor &seqlens_k,
+                  const Tensor &block_table,
+                  std::optional<Tensor> alibi_slopes,
+                  float scale);
+
+} // namespace infinicore::op

python/infinicore/__init__.py

@@ -61,6 +61,7 @@
 from infinicore.ops.equal import equal
 from infinicore.ops.kv_caching import kv_caching
 from infinicore.ops.matmul import matmul
+from infinicore.ops.mha_kvcache import mha_kvcache
 from infinicore.ops.mha_varlen import mha_varlen
 from infinicore.ops.mul import mul
 from infinicore.ops.narrow import narrow
@@ -131,16 +132,15 @@
     "long",
     "short",
     "uint8",
-    # Operations.
-    "addcmul",
-    "atanh",
-    "binary_cross_entropy_with_logits",
-    "cdist",
-    "reciprocal",
+    # Operators.
     "add",
+    "addcmul",
     "add_rms_norm",
     "add_rms_norm_",
+    "atanh",
     "attention",
+    "binary_cross_entropy_with_logits",
+    "cdist",
     "kv_caching",
     "matmul",
     "equal",
@@ -156,11 +156,13 @@
     "from_list",
     "from_numpy",
     "from_torch",
+    "mha_kvcache",
     "mha_varlen",
     "paged_caching",
     "paged_attention",
     "paged_attention_prefill",
     "ones",
+    "reciprocal",
     "strided_empty",
     "strided_from_blob",
     "zeros",

python/infinicore/ops/mha_kvcache.py

@@ -0,0 +1,67 @@
+from typing import Optional
+
+from infinicore.lib import _infinicore
+from infinicore.tensor import Tensor
+
+
+def mha_kvcache(
+    q: Tensor,
+    k_cache: Tensor,
+    v_cache: Tensor,
+    seqlens_k: Tensor,
+    block_table: Tensor,
+    alibi_slopes: Optional[Tensor] = None,
+    scale: float = 1.0,
+    *,
+    out: Optional[Tensor] = None,
+) -> Tensor:
+    """
+    Flash attention KV-cache decode for single-step attention over a paged KV cache.
+
+    This function performs attention decoding using a paged KV cache layout,
+    which is efficient for inference with large sequence lengths.
+
+    Args:
+        q: Query tensor of shape [batch_size, seqlen_q, num_heads, head_size]
+        k_cache: Key cache tensor of shape [num_blocks, block_size, num_heads_k, head_size] (paged layout)
+        v_cache: Value cache tensor of shape [num_blocks, block_size, num_heads_k, head_size] (paged layout)
+        seqlens_k: Total KV length per request of shape [batch_size] (int32)
+        block_table: Block mapping table of shape [batch_size, max_num_blocks_per_seq] (int32)
+        alibi_slopes: Optional ALiBi slopes tensor, if None then ALiBi is disabled
+        scale: Scaling factor for attention scores (typically 1.0/sqrt(head_size))
+        out: Optional output tensor. If provided, the operation will be performed in-place.
+
+    Returns:
+        Output tensor of shape [batch_size, seqlen_q, num_heads, head_size]
+
+    Note:
+        The KV cache uses a paged layout where:
+        - k_cache and v_cache are organized into fixed-size blocks
+        - block_table maps logical positions to physical blocks for each sequence
+        - seqlens_k indicates the current total length of each sequence in the cache
+    """
+    if out is None:
+        return Tensor(
+            _infinicore.mha_kvcache(
+                q._underlying,
+                k_cache._underlying,
+                v_cache._underlying,
+                seqlens_k._underlying,
+                block_table._underlying,
+                alibi_slopes._underlying if alibi_slopes is not None else None,
+                scale,
+            )
+        )
+
+    _infinicore.mha_kvcache_(
+        out._underlying,
+        q._underlying,
+        k_cache._underlying,
+        v_cache._underlying,
+        seqlens_k._underlying,
+        block_table._underlying,
+        alibi_slopes._underlying if alibi_slopes is not None else None,
+        scale,
+    )
+
+    return out

src/infinicore/ops/mha_kvcache/mha_kvcache.cc

@@ -0,0 +1,58 @@
+#include "infinicore/ops/mha_kvcache.hpp"
+#include "../../utils.hpp"
+
+namespace infinicore::op {
+
+INFINICORE_GRAPH_OP_DISPATCHERS_IMPL(MhaKVCache);
+
+MhaKVCache::MhaKVCache(Tensor out,
+                       const Tensor &q,
+                       const Tensor &k_cache,
+                       const Tensor &v_cache,
+                       const Tensor &seqlens_k,
+                       const Tensor &block_table,
+                       std::optional<Tensor> alibi_slopes,
+                       float scale) {
+    INFINICORE_ASSERT_TENSORS_SAME_DEVICE(out, q, k_cache, v_cache, seqlens_k, block_table);
+    INFINICORE_GRAPH_OP_DISPATCH(out->device().getType(),
+                                 out, q, k_cache, v_cache, seqlens_k, block_table, alibi_slopes, scale);
+}
+
+void MhaKVCache::execute(Tensor out,
+                         const Tensor &q,
+                         const Tensor &k_cache,
+                         const Tensor &v_cache,
+                         const Tensor &seqlens_k,
+                         const Tensor &block_table,
+                         std::optional<Tensor> alibi_slopes,
+                         float scale) {
+    INFINICORE_GRAPH_OP_RECORD_OR_RUN(
+        MhaKVCache,
+        out, q, k_cache, v_cache, seqlens_k, block_table, alibi_slopes, scale);
+}
+
+void mha_kvcache_(Tensor out,
+                  const Tensor &q,
+                  const Tensor &k_cache,
+                  const Tensor &v_cache,
+                  const Tensor &seqlens_k,
+                  const Tensor &block_table,
+                  std::optional<Tensor> alibi_slopes,
+                  float scale) {
+    MhaKVCache::execute(out, q, k_cache, v_cache, seqlens_k, block_table, alibi_slopes, scale);
+}
+
+Tensor mha_kvcache(const Tensor &q,
+                   const Tensor &k_cache,
+                   const Tensor &v_cache,
+                   const Tensor &seqlens_k,
+                   const Tensor &block_table,
+                   std::optional<Tensor> alibi_slopes,
+                   float scale) {
+    // Output shape matches q: [batch_size, seqlen_q, num_heads, head_size]
+    auto out = Tensor::empty(q->shape(), q->dtype(), q->device());
+    mha_kvcache_(out, q, k_cache, v_cache, seqlens_k, block_table, alibi_slopes, scale);
+    return out;
+}
+
+} // namespace infinicore::op

src/infinicore/ops/mha_kvcache/mha_kvcache_flashattn.cc

@@ -0,0 +1,100 @@
+#include "infinicore/ops/mha_kvcache.hpp"
+
+#include "infinicore/adaptor/flash_attention_adaptor.hpp"
+
+#include <stdexcept>
+
+namespace infinicore::op::mha_kvcache_impl::flashattn {
+
+struct PlannedMeta {
+    graph::GraphTensor out, q, k_cache, v_cache, seqlens_k, block_table;
+    std::optional<graph::GraphTensor> alibi_slopes;
+    float scale;
+};
+
+void *plan(Tensor out,
+           const Tensor &q,
+           const Tensor &k_cache,
+           const Tensor &v_cache,
+           const Tensor &seqlens_k,
+           const Tensor &block_table,
+           std::optional<Tensor> alibi_slopes,
+           float scale) {
+    return new PlannedMeta{
+        graph::GraphTensor(out),
+        graph::GraphTensor(q),
+        graph::GraphTensor(k_cache),
+        graph::GraphTensor(v_cache),
+        graph::GraphTensor(seqlens_k),
+        graph::GraphTensor(block_table),
+        alibi_slopes ? std::optional<graph::GraphTensor>(graph::GraphTensor(*alibi_slopes)) : std::nullopt,
+        scale};
+}
+
+void run(void *planned_meta) {
+#ifdef ENABLE_FLASH_ATTN
+    c10::cuda::CUDAStreamGuard guard(infinicore::adaptor::get_cuda_stream());
+    auto *p = reinterpret_cast<PlannedMeta *>(planned_meta);
+
+    auto out_tensor = infinicore::adaptor::to_aten_tensor(p->out);
+    auto q = infinicore::adaptor::to_aten_tensor(p->q);
+    auto k_cache = infinicore::adaptor::to_aten_tensor(p->k_cache);
+    auto v_cache = infinicore::adaptor::to_aten_tensor(p->v_cache);
+    auto seqlens_k = std::optional<const at::Tensor>(infinicore::adaptor::to_aten_tensor(p->seqlens_k));
+    auto block_table = std::optional<at::Tensor>(infinicore::adaptor::to_aten_tensor(p->block_table));
+    auto alibi_slopes = p->alibi_slopes
+                          ? std::optional<at::Tensor>(infinicore::adaptor::to_aten_tensor(*p->alibi_slopes))
+                          : std::nullopt;
+
+    std::optional<const at::Tensor> k_new = std::nullopt;
+    std::optional<const at::Tensor> v_new = std::nullopt;
+    std::optional<const at::Tensor> rotary_cos = std::nullopt;
+    std::optional<const at::Tensor> rotary_sin = std::nullopt;
+    std::optional<const at::Tensor> cache_batch_idx = std::nullopt;
+    std::optional<const at::Tensor> leftpad_k = std::nullopt;
+
+    const bool use_dynamic_out = q.dim() == 4 && k_cache.dim() == 4
+                              && q.size(1) == 1 && q.size(2) > k_cache.size(2)
+                              && q.size(3) % 8 == 0 && !alibi_slopes.has_value();
+
+    auto out = use_dynamic_out ? std::optional<at::Tensor>(std::nullopt)
+                               : std::optional<at::Tensor>(out_tensor);
+
+    auto result = flash::mha_fwd_kvcache(
+        q,
+        k_cache,
+        v_cache,
+        k_new,
+        v_new,
+        seqlens_k,
+        rotary_cos,
+        rotary_sin,
+        cache_batch_idx,
+        leftpad_k,
+        block_table,
+        alibi_slopes,
+        out,
+        p->scale,
+        true,
+        -1,
+        -1,
+        0.0f,
+        false,
+        0);
+
+    if (use_dynamic_out) {
+        out_tensor.copy_(result[0]);
+    }
+#else
+    throw std::runtime_error("FlashAttention is not enabled in this build");
+#endif
+}
+
+void cleanup(void **planned_meta_ptr) {
+    delete *reinterpret_cast<PlannedMeta **>(planned_meta_ptr);
+    *planned_meta_ptr = nullptr;
+}
+
+INFINICORE_GRAPH_OP_REGISTER_ALLDEVICE(MhaKVCache, &plan, &run, &cleanup);
+
+} // namespace infinicore::op::mha_kvcache_impl::flashattn

src/infinicore/pybind11/ops.hpp

@@ -22,6 +22,7 @@
 #include "ops/linear.hpp"
 #include "ops/linear_w8a8i8.hpp"
 #include "ops/matmul.hpp"
+#include "ops/mha_kvcache.hpp"
 #include "ops/mha_varlen.hpp"
 #include "ops/mul.hpp"
 #include "ops/paged_attention.hpp"
@@ -54,6 +55,7 @@ inline void bind(py::module &m) {
     bind_linear(m);
     bind_matmul(m);
     bind_mul(m);
+    bind_mha_kvcache(m);
     bind_mha_varlen(m);
     bind_hardswish(m);
     bind_hardtanh(m);