[Kernel][CPU] CPU MLA (#14744)

Signed-off-by: Thien Tran <gau.nernst@yahoo.com.sg>

.buildkite/run-cpu-test.sh

@@ -38,6 +38,8 @@ function cpu_tests() {
     set -e
     pip install -r vllm/requirements/test.txt
     pip install -r vllm/requirements/cpu.txt
+    pytest -v -s tests/kernels/test_cache.py -m cpu_model
+    pytest -v -s tests/kernels/test_mla_decode_cpu.py -m cpu_model
     pytest -v -s tests/models/decoder_only/language -m cpu_model
     pytest -v -s tests/models/embedding/language -m cpu_model
     pytest -v -s tests/models/encoder_decoder/language -m cpu_model

cmake/cpu_extension.cmake

@@ -190,6 +190,7 @@ set(VLLM_EXT_SRC
     "csrc/cpu/cache.cpp"
     "csrc/cpu/utils.cpp"
     "csrc/cpu/layernorm.cpp"
+    "csrc/cpu/mla_decode.cpp"
     "csrc/cpu/pos_encoding.cpp"
     "csrc/cpu/torch_bindings.cpp")
 

csrc/cpu/cache.cpp

@@ -88,6 +88,48 @@ void reshape_and_cache_cpu_impl(
 }
 };  // namespace
 
+template <typename scalar_t>
+void concat_and_cache_mla_cpu_impl(
+    const scalar_t* __restrict__ kv_c,  // [num_tokens, kv_lora_rank]
+    const scalar_t* __restrict__ k_pe,  // [num_tokens, pe_dim]
+    scalar_t* __restrict__ kv_cache,  // [num_blocks, block_size, (kv_lora_rank
+                                      // + pe_dim)]
+    const int64_t* __restrict__ slot_mapping,  // [num_tokens]
+    const int num_tokens,                      //
+    const int block_stride,                    //
+    const int entry_stride,                    //
+    const int kv_c_stride,                     //
+    const int k_pe_stride,                     //
+    const int kv_lora_rank,                    //
+    const int pe_dim,                          //
+    const int block_size                       //
+) {
+#pragma omp parallel for
+  for (int token_idx = 0; token_idx < num_tokens; ++token_idx) {
+    const int64_t slot_idx = slot_mapping[token_idx];
+    // NOTE: slot_idx can be -1 if the token is padded
+    if (slot_idx < 0) {
+      continue;
+    }
+    const int64_t block_idx = slot_idx / block_size;
+    const int64_t block_offset = slot_idx % block_size;
+
+    auto copy = [&](const scalar_t* __restrict__ src,
+                    scalar_t* __restrict__ dst, int src_stride, int dst_stride,
+                    int size, int offset) {
+      for (int i = 0; i < size; i++) {
+        const int64_t src_idx = token_idx * src_stride + i;
+        const int64_t dst_idx =
+            block_idx * block_stride + block_offset * entry_stride + i + offset;
+        dst[dst_idx] = src[src_idx];
+      }
+    };
+
+    copy(kv_c, kv_cache, kv_c_stride, block_stride, kv_lora_rank, 0);
+    copy(k_pe, kv_cache, k_pe_stride, block_stride, pe_dim, kv_lora_rank);
+  }
+}
+
 // Note: the key_caches and value_caches vectors are constant but
 // not the Tensors they contain. The vectors need to be const refs
 // in order to satisfy pytorch's C++ operator registration code.
@@ -134,6 +176,38 @@ void reshape_and_cache(torch::Tensor& key, torch::Tensor& value,
   });
 }
 
+void concat_and_cache_mla(
+    torch::Tensor& kv_c,          // [num_tokens, kv_lora_rank]
+    torch::Tensor& k_pe,          // [num_tokens, pe_dim]
+    torch::Tensor& kv_cache,      // [num_blocks, block_size, (kv_lora_rank +
+                                  // pe_dim)]
+    torch::Tensor& slot_mapping,  // [num_tokens] or [num_actual_tokens]
+    const std::string& kv_cache_dtype, torch::Tensor& scale) {
+  int num_tokens = slot_mapping.size(0);
+  int kv_lora_rank = kv_c.size(1);
+  int pe_dim = k_pe.size(1);
+  int block_size = kv_cache.size(1);
+
+  TORCH_CHECK(kv_cache.size(2) == kv_lora_rank + pe_dim);
+  TORCH_CHECK(kv_cache_dtype != "fp8");
+
+  int kv_c_stride = kv_c.stride(0);
+  int k_pe_stride = k_pe.stride(0);
+  int block_stride = kv_cache.stride(0);
+  int entry_stride = kv_cache.stride(1);
+
+  VLLM_DISPATCH_FLOATING_TYPES(
+      kv_c.scalar_type(), "concat_and_cache_mla_cpu_impl", [&] {
+        CPU_KERNEL_GUARD_IN(concat_and_cache_mla_cpu_impl)
+        concat_and_cache_mla_cpu_impl<scalar_t>(
+            kv_c.data_ptr<scalar_t>(), k_pe.data_ptr<scalar_t>(),
+            kv_cache.data_ptr<scalar_t>(), slot_mapping.data_ptr<int64_t>(),
+            num_tokens, block_stride, entry_stride, kv_c_stride, k_pe_stride,
+            kv_lora_rank, pe_dim, block_size);
+        CPU_KERNEL_GUARD_OUT(concat_and_cache_mla_cpu_impl)
+      });
+}
+
 void swap_blocks(torch::Tensor& src, torch::Tensor& dst,
                  const torch::Tensor& block_mapping) {
   TORCH_CHECK(false, "swap_blocks is unsupported on CPU.")

csrc/cpu/cpu_types_x86.hpp

@@ -130,6 +130,8 @@ struct BF16Vec32 : public Vec<BF16Vec32> {
 
   __m512i reg;
 
+  explicit BF16Vec32() : reg(_mm512_setzero_si512()) {}
+
   explicit BF16Vec32(const void* ptr) : reg((__m512i)_mm512_loadu_si512(ptr)) {}
 
   explicit BF16Vec32(__m512i data) : reg(data) {}

csrc/cpu/mla_decode.cpp

@@ -0,0 +1,393 @@
+#include "cpu_types.hpp"
+#include <float.h>
+
+namespace {
+template <typename scalar_t>
+struct KernelVecType {
+  using qk_load_vec_type = void;
+  using qk_vec_type = void;
+  using v_load_vec_type = void;
+};
+
+template <>
+struct KernelVecType<float> {
+  using qk_load_vec_type = vec_op::FP32Vec16;
+  using qk_vec_type = vec_op::FP32Vec16;
+  using v_load_vec_type = vec_op::FP32Vec16;
+};
+
+template <>
+struct KernelVecType<c10::Half> {
+#if defined(__powerpc64__) || defined(__s390x__)
+  // Power and s390x architecture-specific vector types
+  using qk_load_vec_type = vec_op::FP32Vec16;
+  using qk_vec_type = vec_op::FP32Vec16;
+  using v_load_vec_type = vec_op::FP32Vec16;
+#else
+  // Fallback for other architectures, including x86
+  using qk_load_vec_type = vec_op::FP16Vec16;
+  using qk_vec_type = vec_op::FP32Vec16;
+  using v_load_vec_type = vec_op::FP16Vec16;
+#endif
+};
+
+#ifdef __AVX512BF16__
+template <>
+struct KernelVecType<c10::BFloat16> {
+  using qk_load_vec_type = vec_op::BF16Vec32;
+  using qk_vec_type = vec_op::BF16Vec32;
+  using v_load_vec_type = vec_op::BF16Vec16;
+};
+#elif defined(__aarch64__) && !defined(ARM_BF16_SUPPORT)
+// pass
+#else
+template <>
+struct KernelVecType<c10::BFloat16> {
+  using qk_load_vec_type = vec_op::BF16Vec16;
+  using qk_vec_type = vec_op::FP32Vec16;
+  using v_load_vec_type = vec_op::BF16Vec16;
+};
+#endif
+
+template <int HEAD_DIM, int V_HEAD_DIM, int BLOCK_SIZE, int HEAD_UNROLL,
+          typename qk_vec_type>
+void mla_decode_block_head(
+    const qk_vec_type* __restrict__ q_vecs,          // [HEAD_UNROLL, head_dim]
+    const qk_vec_type* __restrict__ k_vecs,          // [block_size, head_dim]
+    const vec_op::FP32Vec16* __restrict v_vecs_f32,  // [block_size, v_head_dim]
+    float* __restrict__ acc_out,  // [HEAD_UNROLL, v_head_dim]
+    float* __restrict__ acc_lse,  // [HEAD_UNROLL]
+    const float scale, const int num_tokens) {
+  using f32_vec_type = vec_op::FP32Vec16;
+  constexpr int QK_NUM_ELEM = qk_vec_type::VEC_ELEM_NUM;
+  constexpr int V_NUM_ELEM = f32_vec_type::VEC_ELEM_NUM;
+
+  float logits[BLOCK_SIZE][HEAD_UNROLL] = {};  // initialize to zeros
+  float max_val[HEAD_UNROLL];
+  std::fill(max_val, max_val + HEAD_UNROLL, -FLT_MAX);
+
+  f32_vec_type acc_vec[BLOCK_SIZE][HEAD_UNROLL];
+  for (int i = 0; i < HEAD_DIM; i += QK_NUM_ELEM) {
+    // load to registers
+    qk_vec_type q_vec[HEAD_UNROLL];
+
+#pragma unroll
+    for (int unroll = 0; unroll < HEAD_UNROLL; ++unroll)
+      q_vec[unroll] =
+          qk_vec_type{q_vecs[(i + unroll * HEAD_DIM) / QK_NUM_ELEM]};
+
+    for (int block_offset = 0; block_offset < num_tokens; ++block_offset) {
+      qk_vec_type k_vec(k_vecs[(block_offset * HEAD_DIM + i) / QK_NUM_ELEM]);
+
+#pragma unroll
+      for (int unroll = 0; unroll < HEAD_UNROLL; ++unroll)
+        vec_op::fma(acc_vec[block_offset][unroll], q_vec[unroll], k_vec);
+    }
+  }
+
+  for (int block_offset = 0; block_offset < num_tokens; ++block_offset) {
+#pragma unroll
+    for (int unroll = 0; unroll < HEAD_UNROLL; ++unroll) {
+      const float acc = acc_vec[block_offset][unroll].reduce_sum() * scale;
+      logits[block_offset][unroll] = acc;
+      max_val[unroll] = std::max(max_val[unroll], acc);
+    }
+  }
+
+  float sum_exp[HEAD_UNROLL] = {};
+  for (int block_offset = 0; block_offset < num_tokens; ++block_offset) {
+#pragma unroll
+    for (int unroll = 0; unroll < HEAD_UNROLL; ++unroll) {
+      const float val =
+          std::exp(logits[block_offset][unroll] - max_val[unroll]);
+      logits[block_offset][unroll] = val;
+      sum_exp[unroll] += val;
+    }
+  }
+
+  f32_vec_type this_out[V_HEAD_DIM / V_NUM_ELEM][HEAD_UNROLL];
+
+  for (int block_offset = 0; block_offset < num_tokens; ++block_offset) {
+    // load to registers
+    f32_vec_type scale_[HEAD_UNROLL];
+
+#pragma unroll
+    for (int unroll = 0; unroll < HEAD_UNROLL; ++unroll)
+      scale_[unroll] =
+          f32_vec_type{logits[block_offset][unroll] / sum_exp[unroll]};
+
+    for (int i = 0; i < V_HEAD_DIM; i += V_NUM_ELEM) {
+      f32_vec_type v_vec(
+          v_vecs_f32[(block_offset * HEAD_DIM + i) / V_NUM_ELEM]);
+
+#pragma unroll
+      for (int unroll = 0; unroll < HEAD_UNROLL; ++unroll)
+        vec_op::fma(this_out[i / V_NUM_ELEM][unroll], v_vec, scale_[unroll]);
+    }
+  }
+
+  // merge attention state
+  // section 2.2 in https://arxiv.org/pdf/2501.01005
+  f32_vec_type prev_scale[HEAD_UNROLL];
+  f32_vec_type curr_scale[HEAD_UNROLL];
+
+#pragma unroll
+  for (int unroll = 0; unroll < HEAD_UNROLL; ++unroll) {
+    const float prev_lse = acc_lse[unroll];
+    const float curr_lse = std::log(sum_exp[unroll]) +
+                           max_val[unroll];  // add back max_val to get true lse
+    // softmax trick
+    const float max_lse = std::max(prev_lse, curr_lse);
+    const float prev_sum_exp = std::exp(prev_lse - max_lse);
+    const float curr_sum_exp = std::exp(curr_lse - max_lse);
+
+    const float new_sum_exp = prev_sum_exp + curr_sum_exp;
+    acc_lse[unroll] = std::log(new_sum_exp) + max_lse;
+
+    prev_scale[unroll] = f32_vec_type{prev_sum_exp / new_sum_exp};
+    curr_scale[unroll] = f32_vec_type{curr_sum_exp / new_sum_exp};
+  }
+
+  for (int i = 0; i < V_HEAD_DIM; i += V_NUM_ELEM) {
+#pragma unroll
+    for (int unroll = 0; unroll < HEAD_UNROLL; ++unroll) {
+      f32_vec_type o_vec(acc_out + i + V_HEAD_DIM * unroll);
+      o_vec = o_vec * prev_scale[unroll] +
+              this_out[i / V_NUM_ELEM][unroll] * curr_scale[unroll];
+      o_vec.save(acc_out + i + V_HEAD_DIM * unroll);
+    }
+  }
+
+  q_vecs += HEAD_DIM / QK_NUM_ELEM * HEAD_UNROLL;
+  acc_out += V_HEAD_DIM * HEAD_UNROLL;
+}
+
+template <typename scalar_t, int HEAD_DIM, int V_HEAD_DIM, int BLOCK_SIZE,
+          typename qk_vec_type>
+void mla_decode_block(
+    const qk_vec_type* __restrict__ q_vecs,  // [num_heads, head_dim]
+    const scalar_t* __restrict__ kv_cache,   // [block_size, head_dim]
+    float* __restrict__ acc_out,             // [num_heads, v_head_dim]
+    float* __restrict__ acc_lse,             // [num_heads]
+    const int num_heads, const float scale, const int num_tokens) {
+  using qk_load_vec_type = typename KernelVecType<scalar_t>::qk_load_vec_type;
+  static_assert(
+      std::is_same<qk_vec_type,
+                   typename KernelVecType<scalar_t>::qk_vec_type>::value);
+  using v_load_vec_type = typename KernelVecType<scalar_t>::v_load_vec_type;
+  using f32_vec_type = vec_op::FP32Vec16;
+  static_assert(qk_load_vec_type::VEC_ELEM_NUM == qk_vec_type::VEC_ELEM_NUM);
+  static_assert(v_load_vec_type::VEC_ELEM_NUM == f32_vec_type::VEC_ELEM_NUM);
+  constexpr int QK_NUM_ELEM = qk_vec_type::VEC_ELEM_NUM;
+  constexpr int V_NUM_ELEM = v_load_vec_type::VEC_ELEM_NUM;
+
+  const qk_vec_type* k_vecs;
+  const f32_vec_type* v_vecs_f32;
+  float* kv_cache_f32 = nullptr;
+
+  if constexpr (!std::is_same<scalar_t, float>::value) {
+    // convert KV cache block to FP32 to reuse it across query heads and
+    // attn @ V computation, since FP16/BF16->FP32 is expensive.
+    // TODO: move malloc outside of this fn to reuse across iterations.
+    const int nbytes = BLOCK_SIZE * HEAD_DIM * sizeof(float);
+    kv_cache_f32 = static_cast<float*>(std::aligned_alloc(64, nbytes));
+
+    for (int block_offset = 0; block_offset < num_tokens; ++block_offset)
+      for (int i = 0; i < HEAD_DIM; i += V_NUM_ELEM) {
+        v_load_vec_type kv_load_vec(kv_cache + block_offset * HEAD_DIM + i);
+        f32_vec_type kv_vec_f32(kv_load_vec);
+        kv_vec_f32.save(kv_cache_f32 + block_offset * HEAD_DIM + i);
+      }
+
+    if constexpr (std::is_same<qk_load_vec_type, qk_vec_type>::value) {
+      // for AVX512_BF16, Q @ K.T uses BF16 for K (no conversion)
+      // NOTE: in this case, we only need to convert the V section to FP32.
+      // But for simplicity, we will convert the whole KV block to FP32.
+      k_vecs = reinterpret_cast<const qk_vec_type*>(kv_cache);
+    } else {
+      k_vecs = reinterpret_cast<const qk_vec_type*>(kv_cache_f32);
+    }
+
+    // attn @ V always use FP32 for V, since attn is FP32.
+    v_vecs_f32 = reinterpret_cast<const f32_vec_type*>(kv_cache_f32);
+
+  } else {
+    // KV cache is FP32. don't need to do anything.
+    k_vecs = reinterpret_cast<const qk_vec_type*>(kv_cache);
+    v_vecs_f32 = reinterpret_cast<const f32_vec_type*>(kv_cache);
+  }
+
+  // compute 2 heads at the same time to improve ILP and
+  // take advantage of register cache for K and V.
+  constexpr int HEAD_UNROLL = 2;
+  for (int iter = 0; iter < num_heads / HEAD_UNROLL; ++iter) {
+    mla_decode_block_head<HEAD_DIM, V_HEAD_DIM, BLOCK_SIZE, HEAD_UNROLL>(
+        q_vecs, k_vecs, v_vecs_f32, acc_out, acc_lse, scale, num_tokens);
+
+    q_vecs += HEAD_UNROLL * HEAD_DIM / QK_NUM_ELEM;
+    acc_out += HEAD_UNROLL * V_HEAD_DIM;
+    acc_lse += HEAD_UNROLL;
+  }
+
+  // take care of the remaining heads
+  for (int iter = 0; iter < num_heads % HEAD_UNROLL; ++iter) {
+    mla_decode_block_head<HEAD_DIM, V_HEAD_DIM, BLOCK_SIZE, 1>(
+        q_vecs, k_vecs, v_vecs_f32, acc_out, acc_lse, scale, num_tokens);
+
+    q_vecs += HEAD_DIM / QK_NUM_ELEM;
+    acc_out += V_HEAD_DIM;
+    acc_lse += 1;
+  }
+
+  if (kv_cache_f32 != nullptr) {
+    std::free(kv_cache_f32);
+  }
+}
+}  // namespace
+
+template <typename scalar_t, int HEAD_DIM, int V_HEAD_DIM, int BLOCK_SIZE>
+void mla_decode_kvcache_cpu_impl(
+    scalar_t* __restrict__ out,             // [num_seqs, num_heads, v_head_dim]
+    const scalar_t* __restrict__ q,         // [num_seqs, num_heads, head_dim]
+    const scalar_t* __restrict__ kv_cache,  // [num_blocks, block_size,
+                                            // head_dim]
+    const int num_heads, const float scale,
+    const int* __restrict__ block_tables,  // [num_seqs, max_num_blocks_per_seq]
+    const int* __restrict__ seq_lens,      // [num_seqs]
+    const int max_num_blocks_per_seq, const int o_stride, const int q_stride,
+    const int kv_stride, const int num_seqs) {
+  using qk_load_vec_type = typename KernelVecType<scalar_t>::qk_load_vec_type;
+  using qk_vec_type = typename KernelVecType<scalar_t>::qk_vec_type;
+  constexpr int QK_NUM_ELEM = qk_vec_type::VEC_ELEM_NUM;
+
+  // shared across threads
+  const int max_threads = omp_get_max_threads();
+  const int acc_out_nbytes =
+      max_threads * num_heads * V_HEAD_DIM * sizeof(float);
+  float* acc_out = static_cast<float*>(std::aligned_alloc(64, acc_out_nbytes));
+  std::vector<float> acc_lse(max_threads * num_heads);
+
+  // allocate memory to pre-convert query to FP32 later
+  float* q_f32;
+  constexpr bool PRE_CONVERT_QUERY =
+      !std::is_same<scalar_t, float>::value &&
+      std::is_same<qk_vec_type, vec_op::FP32Vec16>::value;
+  if constexpr (PRE_CONVERT_QUERY) {
+    const int q_f32_nbytes = num_heads * HEAD_DIM * sizeof(float);
+    q_f32 = static_cast<float*>(std::aligned_alloc(64, q_f32_nbytes));
+  }
+
+#pragma omp parallel
+  {
+    const int num_threads = omp_get_num_threads();
+    const int thread_id = omp_get_thread_num();
+    float* __restrict__ acc_out_thread =
+        acc_out + thread_id * num_heads * V_HEAD_DIM;
+    float* __restrict__ acc_lse_thread = acc_lse.data() + thread_id * num_heads;
+
+    for (int seq_idx = 0; seq_idx < num_seqs; ++seq_idx) {
+      // reset accumulator
+      std::fill(acc_out_thread, acc_out_thread + num_heads * V_HEAD_DIM, 0.0f);
+      std::fill(acc_lse_thread, acc_lse_thread + num_heads, -FLT_MAX);
+
+      const int seq_len = seq_lens[seq_idx];
+      const int block_num = (seq_len + BLOCK_SIZE - 1) / BLOCK_SIZE;
+      const int last_block_size = seq_len - (block_num - 1) * BLOCK_SIZE;
+
+      const qk_vec_type* q_vecs;
+      if constexpr (PRE_CONVERT_QUERY) {
+// pre-convert query to FP32 since FP16/BF16->FP32 is slow.
+#pragma omp for
+        for (int i = 0; i < num_heads * HEAD_DIM; i += QK_NUM_ELEM) {
+          qk_load_vec_type q_load_vec(q + seq_idx * q_stride + i);
+          qk_vec_type q_vec(q_load_vec);
+          q_vec.save(q_f32 + i);
+        }
+        q_vecs = reinterpret_cast<const qk_vec_type*>(q_f32);
+      } else {
+        q_vecs = reinterpret_cast<const qk_vec_type*>(q + seq_idx * q_stride);
+      }
+
+#pragma omp for
+      for (int block_idx = 0; block_idx < block_num; ++block_idx) {
+        const int physical_block_idx =
+            block_tables[seq_idx * max_num_blocks_per_seq + block_idx];
+        const int num_tokens =
+            block_idx < block_num - 1 ? BLOCK_SIZE : last_block_size;
+
+        mla_decode_block<scalar_t, HEAD_DIM, V_HEAD_DIM, BLOCK_SIZE>(
+            q_vecs, kv_cache + physical_block_idx * kv_stride, acc_out_thread,
+            acc_lse_thread, num_heads, scale, num_tokens);
+      }
+
+// merge attention states across threads
+// section 2.2 in https://arxiv.org/pdf/2501.01005
+// each thread is responsible for 1 head
+#pragma omp for
+      for (int head_idx = 0; head_idx < num_heads; ++head_idx) {
+        float* acc_lse_head = acc_lse.data() + head_idx;
+        float* acc_out_head = acc_out + head_idx * V_HEAD_DIM;
+
+        float max_val = -FLT_MAX;
+        for (int thread_id_ = 0; thread_id_ < num_threads; ++thread_id_) {
+          max_val = std::max(max_val, acc_lse_head[thread_id_ * num_heads]);
+        }
+
+        float sum_exp = 0.0f;
+        for (int thread_id_ = 0; thread_id_ < num_threads; ++thread_id_) {
+          float val = std::exp(acc_lse_head[thread_id_ * num_heads] - max_val);
+          acc_lse_head[thread_id_ * num_heads] = val;
+          sum_exp += val;
+        }
+
+        float inv_sum = 1.0f / sum_exp;
+        float out_head[V_HEAD_DIM] = {};
+        for (int thread_id_ = 0; thread_id_ < num_threads; ++thread_id_) {
+          float scale_ = acc_lse_head[thread_id_ * num_heads] * inv_sum;
+          for (int i = 0; i < V_HEAD_DIM; ++i) {
+            out_head[i] +=
+                acc_out_head[thread_id_ * num_heads * V_HEAD_DIM + i] * scale_;
+          }
+        }
+
+        for (int i = 0; i < V_HEAD_DIM; ++i) {
+          vec_op::storeFP32(out_head[i], out + seq_idx * o_stride +
+                                             head_idx * V_HEAD_DIM + i);
+        }
+      }
+    }
+  }
+  if (PRE_CONVERT_QUERY) {
+    std::free(q_f32);
+  }
+  std::free(acc_out);
+}
+
+void mla_decode_kvcache(torch::Tensor& out, torch::Tensor& query,
+                        torch::Tensor& kv_cache, double scale,
+                        torch::Tensor& block_tables, torch::Tensor& seq_lens) {
+  const int num_seqs = query.size(0);
+  const int num_heads = query.size(1);
+  const int head_dim = query.size(2);
+  const int block_size = kv_cache.size(1);
+  const int v_head_dim = out.size(2);
+
+  const int max_num_blocks_per_seq = block_tables.size(1);
+  const int o_stride = out.stride(0);
+  const int q_stride = query.stride(0);
+  const int kv_stride = kv_cache.stride(0);
+
+  VLLM_DISPATCH_FLOATING_TYPES(
+      query.scalar_type(), "mla_decode_kvcache_cpu_impl", [&] {
+        CPU_KERNEL_GUARD_IN(mla_decode_kvcache_cpu_impl)
+        if (head_dim == 576 && v_head_dim == 512 && block_size == 16)
+          mla_decode_kvcache_cpu_impl<scalar_t, 576, 512, 16>(
+              out.data_ptr<scalar_t>(), query.data_ptr<scalar_t>(),
+              kv_cache.data_ptr<scalar_t>(), num_heads, scale,
+              block_tables.data_ptr<int>(), seq_lens.data_ptr<int>(),
+              max_num_blocks_per_seq, o_stride, q_stride, kv_stride, num_seqs);
+        else
+          TORCH_CHECK(false, "Unsupported block size: ", block_size);
+        CPU_KERNEL_GUARD_OUT(mla_decode_kvcache_cpu_impl)
+      });
+}

csrc/cpu/torch_bindings.cpp

@@ -18,6 +18,10 @@ void int8_scaled_mm_azp(torch::Tensor& c, const torch::Tensor& a,
                         const std::optional<torch::Tensor>& azp,
                         const std::optional<torch::Tensor>& bias);
 
+void mla_decode_kvcache(torch::Tensor& out, torch::Tensor& query,
+                        torch::Tensor& kv_cache, double scale,
+                        torch::Tensor& block_tables, torch::Tensor& seq_lens);
+
 TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
   // vLLM custom ops
 
@@ -150,6 +154,14 @@ TORCH_LIBRARY_EXPAND(CONCAT(TORCH_EXTENSION_NAME, _cache_ops), cache_ops) {
       "                  str kv_cache_dtype,"
       "                  Tensor k_scale, Tensor v_scale) -> ()");
   cache_ops.impl("reshape_and_cache", torch::kCPU, &reshape_and_cache);
+
+  cache_ops.def(
+      "concat_and_cache_mla(Tensor kv_c, Tensor k_pe,"
+      "                     Tensor! kv_cache,"
+      "                     Tensor slot_mapping,"
+      "                     str kv_cache_dtype,"
+      "                     Tensor scale) -> ()");
+  cache_ops.impl("concat_and_cache_mla", torch::kCPU, &concat_and_cache_mla);
 }
 
 TORCH_LIBRARY_EXPAND(CONCAT(TORCH_EXTENSION_NAME, _utils), utils) {
@@ -157,4 +169,12 @@ TORCH_LIBRARY_EXPAND(CONCAT(TORCH_EXTENSION_NAME, _utils), utils) {
   utils.def("init_cpu_threads_env(str cpu_ids) -> str", &init_cpu_threads_env);
 }
 
+TORCH_LIBRARY_EXPAND(CONCAT(TORCH_EXTENSION_NAME, _cpu), cpu_ops) {
+  cpu_ops.def(
+      "mla_decode_kvcache("
+      "   Tensor! out, Tensor query, Tensor kv_cache,"
+      "   float scale, Tensor block_tables, Tensor seq_lens) -> ()");
+  cpu_ops.impl("mla_decode_kvcache", torch::kCPU, &mla_decode_kvcache);
+}
+
 REGISTER_EXTENSION(TORCH_EXTENSION_NAME)

tests/kernels/test_cache.py

@@ -749,3 +749,72 @@ def test_gather_cache_mla(kv_lora_rank, qk_rope_head_dim, block_size,
 
     ops.gather_cache(src_cache, dst, block_table, cu_seq_lens, batch_size)
     torch.testing.assert_close(dst, expected)
+
+
+@pytest.mark.parametrize("kv_lora_rank", KV_LORA_RANKS)
+@pytest.mark.parametrize("qk_rope_head_dim", QK_ROPE_HEAD_DIMS)
+@pytest.mark.parametrize("num_tokens", NUM_TOKENS_MLA)
+@pytest.mark.parametrize("block_size", BLOCK_SIZES_MLA)
+@pytest.mark.parametrize("num_blocks", NUM_BLOCKS_MLA)
+@pytest.mark.parametrize("dtype", DTYPES)
+@pytest.mark.parametrize("seed", SEEDS)
+@pytest.mark.cpu_model
+@pytest.mark.skipif(not current_platform.is_cpu(), reason="CPU only")
+@torch.inference_mode()
+def test_concat_and_cache_mla_cpu(
+    kv_lora_rank: int,
+    qk_rope_head_dim: int,
+    num_tokens: int,
+    block_size: int,
+    num_blocks: int,
+    dtype: torch.dtype,
+    seed: int,
+) -> None:
+    device = "cpu"
+    kv_cache_dtype = "auto"
+    current_platform.seed_everything(seed)
+    torch.set_default_device(device)
+
+    total_slots = num_blocks * block_size
+    slot_mapping_lst = random.sample(range(total_slots), num_tokens)
+    slot_mapping = torch.tensor(slot_mapping_lst,
+                                dtype=torch.long,
+                                device=device)
+
+    kv_c = torch.randn(num_tokens, kv_lora_rank, dtype=dtype, device=device)
+    k_pe = torch.randn(num_tokens,
+                       qk_rope_head_dim,
+                       dtype=dtype,
+                       device=device)
+    entry_size = kv_lora_rank + qk_rope_head_dim
+
+    scale = torch.tensor(0.1, dtype=torch.float32, device=device)
+    kv_cache = _create_mla_cache(num_blocks, block_size, entry_size, dtype,
+                                 kv_cache_dtype, device)
+    ref_temp = torch.zeros(*kv_cache.shape, dtype=dtype, device=device)
+
+    for i in range(num_tokens):
+        slot = slot_mapping[i].item()
+        block_idx = slot // block_size
+        block_offset = slot % block_size
+        ref_temp[block_idx, block_offset, :kv_lora_rank] = kv_c[i]
+        ref_temp[block_idx, block_offset, kv_lora_rank:] = k_pe[i]
+
+    if kv_cache_dtype == "fp8":
+        ref_kv_cache = torch.empty_like(ref_temp, dtype=kv_cache.dtype)
+        ops.convert_fp8(ref_kv_cache,
+                        ref_temp,
+                        scale.item(),
+                        kv_dtype=kv_cache_dtype)
+    else:
+        ref_kv_cache = ref_temp
+
+    opcheck(
+        torch.ops._C_cache_ops.concat_and_cache_mla,
+        (kv_c, k_pe, kv_cache, slot_mapping, kv_cache_dtype, scale),
+        test_utils=DEFAULT_OPCHECK_TEST_UTILS,
+    )
+
+    ops.concat_and_cache_mla(kv_c, k_pe, kv_cache, slot_mapping,
+                             kv_cache_dtype, scale)
+    torch.testing.assert_close(kv_cache, ref_kv_cache)

tests/kernels/test_mla_decode_cpu.py

@@ -0,0 +1,94 @@
+# SPDX-License-Identifier: Apache-2.0
+import pytest
+import torch
+import torch.nn.functional as F
+from torch import Tensor
+
+import vllm._custom_ops as ops
+from vllm.platforms import current_platform
+
+
+def cdiv(a, b):
+    return (a + b - 1) // b
+
+
+def ref_mla(
+        out: Tensor,  # (bs, num_heads, v_head_dim)
+        query: Tensor,  # (bs, num_heads, head_dim)
+        kv_cache: Tensor,  # (num_blocks, block_size, head_dim)
+        scale: float,
+        block_tables: Tensor,  # (bs, max_num_blocks)
+        seq_lens: Tensor,  # (bs,)
+):
+    bs, num_heads, v_head_dim = out.shape
+    head_dim = query.shape[2]
+
+    for i in range(bs):
+        # gather and flatten KV-cache
+        kv = kv_cache[
+            block_tables[i]]  # (max_num_blocks, block_size, head_dim)
+        kv = kv.view(1, -1,
+                     head_dim)[:, :seq_lens[i]]  # (1, seq_len, head_dim)
+        v = kv[:, :, :v_head_dim]
+
+        q = query[i].view(num_heads, 1, head_dim)
+        o = F.scaled_dot_product_attention(q,
+                                           kv,
+                                           v,
+                                           scale=scale,
+                                           enable_gqa=True)
+        out[i] = o.view(num_heads, v_head_dim)
+
+    return out
+
+
+@pytest.mark.parametrize("bs", [4])
+@pytest.mark.parametrize("mean_seq_len", [256])
+@pytest.mark.parametrize("h_q", [16])
+@pytest.mark.parametrize("d", [576])
+@pytest.mark.parametrize("dv", [512])
+@pytest.mark.parametrize("block_size", [16])
+@pytest.mark.parametrize("dtype", [torch.float, torch.half, torch.bfloat16])
+@pytest.mark.parametrize("varlen", [False, True])
+@pytest.mark.cpu_model
+@pytest.mark.skipif(not current_platform.is_cpu(), reason="CPU only")
+def test_mla_decode_cpu(
+    bs: int,
+    mean_seq_len: int,
+    h_q: int,
+    d: int,
+    dv: int,
+    block_size: int,
+    dtype: torch.dtype,
+    varlen: bool,
+):
+    torch.set_default_dtype(dtype)
+    torch.manual_seed(0)
+
+    scale = d**(-0.5)
+    if varlen:
+        seq_lens = torch.empty(bs).normal_(mean_seq_len, mean_seq_len / 2)
+        seq_lens = seq_lens.clip(2).to(torch.int32)
+    else:
+        seq_lens = torch.full((bs, ), mean_seq_len, dtype=torch.int32)
+    max_seq_len = seq_lens.max().item()
+    seqlen_pad = cdiv(max_seq_len, 256) * 256  # is this necessary?
+
+    q = torch.randn(bs, h_q, d)
+    block_table = torch.arange(bs * seqlen_pad // block_size,
+                               dtype=torch.int32)
+    block_table = block_table.view(bs, seqlen_pad // block_size)
+
+    kv_cache = torch.randn(block_table.numel(), block_size, d)
+    for i, seq_len in enumerate(seq_lens.tolist()):
+        kv_cache.view(bs, seqlen_pad, d)[i, seq_len:] = float("nan")
+
+    out_mla = q.new_zeros(bs, h_q, dv)
+    ops.mla_decode_kvcache_cpu(out_mla, q, kv_cache, scale, block_table,
+                               seq_lens)
+
+    out_ref = q.new_zeros(bs, h_q, dv)
+    ref_mla(out_ref, q, kv_cache, scale, block_table, seq_lens)
+
+    assert not out_mla.isnan().any(), "Likely read out of bounds"
+    torch.testing.assert_close(out_mla, out_ref)

vllm/_custom_ops.py

@@ -124,6 +124,18 @@ def paged_attention_rocm(
                                       kv_cache_dtype, k_scale, v_scale)
 
 
+def mla_decode_kvcache_cpu(
+    out: torch.Tensor,
+    query: torch.Tensor,
+    kv_cache: torch.Tensor,
+    scale: float,
+    block_tables: torch.Tensor,
+    seq_lens: torch.Tensor,
+) -> None:
+    torch.ops._C_cpu.mla_decode_kvcache(out, query, kv_cache, scale,
+                                        block_tables, seq_lens)
+
+
 # pos encoding ops
 def rotary_embedding(
     positions: torch.Tensor,

vllm/_ipex_ops.py

@@ -187,15 +187,28 @@ class ipex_ops:
         gen_: torch.Generator,
         logits_soft_cap: float,
     ) -> None:
+        if ipex.__version__.endswith("cpu"):
+            if logits_soft_cap != 0.0:
+                raise ValueError("IPEX CPU does not support logits_soft_cap")
             ipex.llm.functional.varlen_attention(query.contiguous(),
                                                  key.contiguous(),
                                                  value.contiguous(), out,
-                                             seqlen_q.int(), seqlen_k.int(),
-                                             max_seqlen_q, max_seqlen_k,
-                                             pdropout, softmax_scale,
-                                             zero_tensors, is_causal,
-                                             return_softmax, gen_,
-                                             logits_soft_cap)
+                                                 seqlen_q.int(),
+                                                 seqlen_k.int(), max_seqlen_q,
+                                                 max_seqlen_k, pdropout,
+                                                 softmax_scale, zero_tensors,
+                                                 is_causal, return_softmax,
+                                                 gen_)
+        else:  # XPU build
+            ipex.llm.functional.varlen_attention(query.contiguous(),
+                                                 key.contiguous(),
+                                                 value.contiguous(), out,
+                                                 seqlen_q.int(),
+                                                 seqlen_k.int(), max_seqlen_q,
+                                                 max_seqlen_k, pdropout,
+                                                 softmax_scale, zero_tensors,
+                                                 is_causal, return_softmax,
+                                                 gen_, logits_soft_cap)
 
     @staticmethod
     def reshape_and_cache(

vllm/attention/backends/cpu_mla.py

@@ -0,0 +1,303 @@
+# SPDX-License-Identifier: Apache-2.0
+
+from dataclasses import dataclass
+from typing import Any, Dict, List, Optional, Tuple, Type
+
+import torch
+
+import vllm._custom_ops as ops
+from vllm._ipex_ops import ipex_ops
+from vllm.attention.backends.abstract import (AttentionBackend,
+                                              AttentionMetadataBuilder,
+                                              AttentionType,
+                                              is_quantized_kv_cache)
+from vllm.attention.backends.mla.common import MLACommonImpl, MLACommonState
+from vllm.attention.backends.torch_sdpa import TorchSDPAMetadata
+from vllm.utils import make_tensor_with_pad
+from vllm.worker.cpu_model_runner import ModelInputForCPUBuilder
+
+
+class CPUMLABackend(AttentionBackend):
+
+    @staticmethod
+    def get_name() -> str:
+        return "CPU_MLA"
+
+    @staticmethod
+    def get_metadata_cls() -> Type["CPUMLAMetadata"]:
+        return CPUMLAMetadata
+
+    @staticmethod
+    def get_builder_cls() -> Type["CPUMLAMetadataBuilder"]:
+        return CPUMLAMetadataBuilder
+
+    @staticmethod
+    def get_state_cls() -> Type["MLACommonState"]:
+        return MLACommonState
+
+    @staticmethod
+    def get_impl_cls() -> Type["CPUMLAImpl"]:
+        return CPUMLAImpl
+
+    @staticmethod
+    def get_kv_cache_shape(
+        num_blocks: int,
+        block_size: int,
+        num_kv_heads: int,  # assumed to be 1 for MLA
+        head_size: int,
+    ) -> Tuple[int, ...]:
+        return (num_blocks, block_size, head_size)
+
+    @staticmethod
+    def swap_blocks(
+        src_kv_cache: torch.Tensor,
+        dst_kv_cache: torch.Tensor,
+        src_to_dst: torch.Tensor,
+    ) -> None:
+        ops.swap_blocks(src_kv_cache, dst_kv_cache, src_to_dst)
+
+    @staticmethod
+    def copy_blocks(
+        kv_caches: List[torch.Tensor],
+        src_to_dists: torch.Tensor,
+    ) -> None:
+        ops.copy_blocks_mla(kv_caches, src_to_dists)
+
+    @staticmethod
+    def get_supported_head_sizes() -> List[int]:
+        return [576]
+
+
+@dataclass
+class CPUMLAMetadata(TorchSDPAMetadata):
+    # New for MLA
+    # Input positions for rotrary embeddings since for MLA the rotary
+    # position embeddings are applied inside the attention backend
+    input_positions: torch.Tensor = None
+
+    # required by MLACommonImpl
+    is_profile_run: bool = False
+
+
+class CPUMLAMetadataBuilder(AttentionMetadataBuilder[CPUMLAMetadata]):
+
+    def __init__(self, input_builder: ModelInputForCPUBuilder) -> None:
+        self.chunked_prefill = input_builder.chunked_prefill
+        self.input_builder = input_builder
+        assert not self.chunked_prefill, \
+            "chunked prefill is currently not supported"
+
+    def prepare(self):
+        self.input_data = self.input_builder.input_data
+
+    def build(self, seq_lens, query_lens, cuda_graph_pad_size, batch_size):
+        input_data = self.input_data
+        prefill_seq_lens = seq_lens[0:input_data.num_prefills]
+        prefill_query_lens = query_lens[0:input_data.num_prefills]
+        slot_mapping = torch.tensor(input_data.slot_mapping,
+                                    dtype=torch.long,
+                                    device="cpu")
+
+        # metadata for prefill
+        if input_data.num_prefills > 0:
+            query_lens_tensor = torch.tensor(prefill_query_lens,
+                                             dtype=torch.int32,
+                                             device="cpu")
+            kv_lens_tensor = torch.tensor(prefill_seq_lens,
+                                          dtype=torch.int32,
+                                          device="cpu")
+            query_start_loc = torch.zeros(input_data.num_prefills + 1,
+                                          dtype=torch.int32,
+                                          device="cpu")
+            kv_start_loc = torch.zeros(input_data.num_prefills + 1,
+                                       dtype=torch.int32,
+                                       device="cpu")
+            torch.cumsum(query_lens_tensor,
+                         dim=0,
+                         dtype=torch.int32,
+                         out=query_start_loc[1:])
+            torch.cumsum(kv_lens_tensor,
+                         dim=0,
+                         dtype=torch.int32,
+                         out=kv_start_loc[1:])
+            max_query_len = max(prefill_query_lens)
+            max_kv_len = max(prefill_seq_lens)
+
+            # for chunked-prefill
+            if self.chunked_prefill:
+                prefill_block_tables = make_tensor_with_pad(
+                    self.input_data.prefill_block_tables,
+                    pad=0,
+                    dtype=torch.int32,
+                    device="cpu",
+                )
+            else:
+                prefill_block_tables = None
+
+        else:
+            query_start_loc = None
+            kv_start_loc = None
+            max_query_len = None
+            max_kv_len = None
+            prefill_block_tables = None
+
+        # metadata for decode
+        if input_data.num_decode_tokens != 0:
+            seq_lens_tensor = torch.tensor(
+                input_data.seq_lens[input_data.num_prefills:],
+                dtype=torch.int32,
+                device="cpu",
+            )
+            block_tables = make_tensor_with_pad(
+                self.input_data.decode_block_tables,
+                pad=0,
+                dtype=torch.int32,
+                device="cpu",
+            )
+        else:
+            block_tables = torch.tensor([])
+            seq_lens_tensor = torch.tensor(
+                input_data.seq_lens[:input_data.num_prefills],
+                dtype=torch.int32,
+                device="cpu",
+            )
+
+        # For multi-modal models
+        placeholder_index_maps = None
+        if len(input_data.multi_modal_inputs_list) != 0:
+            placeholder_index_maps = {
+                modality: placeholder_map.index_map()
+                for modality, placeholder_map in
+                input_data.multi_modal_placeholder_maps.items()
+            }
+
+        return CPUMLAMetadata(
+            chunked_prefill=self.chunked_prefill,
+            seq_lens=prefill_seq_lens,
+            seq_lens_tensor=seq_lens_tensor,
+            max_query_len=max_query_len,
+            max_kv_len=max_kv_len,
+            query_start_loc=query_start_loc,
+            kv_start_loc=kv_start_loc,
+            max_decode_seq_len=input_data.max_decode_seq_len,
+            num_prefills=input_data.num_prefills,
+            num_prefill_tokens=input_data.num_prefill_tokens,
+            num_decode_tokens=input_data.num_decode_tokens,
+            block_tables=block_tables,
+            prefill_block_tables=prefill_block_tables,
+            slot_mapping=slot_mapping,
+            multi_modal_placeholder_index_maps=placeholder_index_maps,
+            enable_kv_scales_calculation=False,
+            input_positions=torch.tensor([self.input_data.input_positions]))
+
+
+class CPUMLAImpl(MLACommonImpl[CPUMLAMetadata]):
+
+    def __init__(
+            self,
+            num_heads: int,
+            head_size: int,
+            scale: float,
+            num_kv_heads: int,
+            alibi_slopes: Optional[List[float]],
+            sliding_window: Optional[int],
+            kv_cache_dtype: str,
+            blocksparse_params: Optional[Dict[str, Any]],
+            logits_soft_cap: Optional[float],
+            attn_type: str,
+            # MLA Specific Arguments
+            **mla_args) -> None:
+        super().__init__(num_heads, head_size, scale, num_kv_heads,
+                         alibi_slopes, sliding_window, kv_cache_dtype,
+                         blocksparse_params, logits_soft_cap, attn_type,
+                         **mla_args)
+
+        unsupported_features = [
+            alibi_slopes, sliding_window, blocksparse_params, logits_soft_cap
+        ]
+        if any(unsupported_features):
+            raise NotImplementedError(
+                "CPUMLAImpl does not support one of the following: "
+                "alibi_slopes, sliding_window, blocksparse_params, "
+                "logits_soft_cap")
+
+        if attn_type != AttentionType.DECODER:
+            raise NotImplementedError("Encoder self-attention and "
+                                      "encoder/decoder cross-attention "
+                                      "are not implemented for "
+                                      "CPUMLAImpl")
+
+        # states is implemented.
+        if is_quantized_kv_cache(self.kv_cache_dtype):
+            raise NotImplementedError(
+                "CPUMLAImpl with FP8 KV cache not yet supported")
+
+    def _forward_prefill(
+            self,
+            q: torch.Tensor,
+            kv_c_normed: torch.Tensor,
+            k_pe: torch.Tensor,
+            kv_c_and_k_pe_cache: torch.Tensor,
+            attn_metadata: CPUMLAMetadata,  # type: ignore[override]
+    ) -> torch.Tensor:
+
+        prefill_metadata = attn_metadata.prefill_metadata
+        assert prefill_metadata is not None
+
+        kv_nope = self.kv_b_proj(kv_c_normed)[0].view(\
+            -1, self.num_heads, self.qk_nope_head_dim + self.v_head_dim)
+        k_nope, v = kv_nope\
+            .split([self.qk_nope_head_dim, self.v_head_dim], dim=-1)
+
+        k = torch.cat((k_nope, k_pe.expand((*k_nope.shape[:-1], -1))), dim=-1)
+
+        # For MLA the v head dim is smaller than qk head dim so we pad out
+        # v with 0s to match the qk head dim
+        v_padded = torch.nn.functional.pad(v, [0, q.shape[-1] - v.shape[-1]],
+                                           value=0)
+
+        output = torch.empty_like(q)
+        ipex_ops.varlen_attention(
+            query=q,
+            key=k,
+            value=v_padded,
+            out=output,
+            seqlen_q=prefill_metadata.query_start_loc,
+            seqlen_k=prefill_metadata.query_start_loc,
+            max_seqlen_q=prefill_metadata.max_query_len,
+            max_seqlen_k=prefill_metadata.max_query_len,
+            pdropout=0.0,
+            softmax_scale=self.scale,
+            zero_tensors=False,
+            is_causal=True,
+            return_softmax=False,
+            gen_=None,
+            logits_soft_cap=0.0,
+        )
+
+        # remove padding
+        output = output.view(-1, self.num_heads,
+                             q.shape[-1])[..., :v.shape[-1]]
+        output = output.reshape(-1, self.num_heads * v.shape[-1])
+        return self.o_proj(output)[0]
+
+    def _forward_decode(
+            self,
+            q_nope: torch.Tensor,
+            q_pe: torch.Tensor,
+            kv_c_and_k_pe_cache: torch.Tensor,
+            attn_metadata: CPUMLAMetadata,  # type: ignore[override]
+    ) -> torch.Tensor:
+        assert kv_c_and_k_pe_cache.numel() > 0
+
+        decode_meta = attn_metadata.decode_metadata
+        assert decode_meta is not None
+
+        q = torch.cat([q_nope, q_pe], dim=-1)
+        o = q.new_empty(q.shape[0], self.num_heads, self.kv_lora_rank)
+
+        # Run MQA
+        ops.mla_decode_kvcache_cpu(o, q, kv_c_and_k_pe_cache, self.scale,
+                                   decode_meta.block_tables,
+                                   decode_meta.seq_lens_tensor)
+        return self._v_up_proj_and_o_proj(o)

vllm/attention/backends/mla/common.py

@@ -204,7 +204,6 @@ from vllm.attention.backends.abstract import (AttentionBackend, AttentionLayer,
 from vllm.attention.backends.utils import (PAD_SLOT_ID, compute_slot_mapping,
                                            compute_slot_mapping_start_idx,
                                            is_block_tables_empty)
-from vllm.attention.ops.triton_merge_attn_states import merge_attn_states
 from vllm.model_executor.layers.linear import (ColumnParallelLinear,
                                                LinearBase, RowParallelLinear,
                                                UnquantizedLinearMethod)
@@ -212,18 +211,27 @@ from vllm.model_executor.layers.rotary_embedding import (
     DeepseekScalingRotaryEmbedding, RotaryEmbedding)
 from vllm.multimodal import MultiModalPlaceholderMap
 from vllm.platforms import current_platform
+from vllm.triton_utils import HAS_TRITON
 from vllm.utils import async_tensor_h2d, cdiv, make_tensor_with_pad, round_down
 from vllm.vllm_flash_attn.fa_utils import get_flash_attn_version
 
+if HAS_TRITON:
+    from vllm.attention.ops.triton_flash_attention import triton_attention
+    from vllm.attention.ops.triton_merge_attn_states import merge_attn_states
+else:
+    merge_attn_states = None
+    triton_attention = None
+
 try:
     from vllm.vllm_flash_attn import flash_attn_varlen_func
     is_vllm_fa = True
 except ImportError:
+    is_vllm_fa = False
+    try:
         # For rocm use upstream flash attention
         from flash_attn import flash_attn_varlen_func
-    is_vllm_fa = False
-
-from vllm.attention.ops.triton_flash_attention import triton_attention
+    except ImportError:
+        flash_attn_varlen_func = None
 
 if TYPE_CHECKING:
     from vllm.worker.model_runner import (ModelInputForGPUBuilder,

vllm/platforms/cpu.py

@@ -37,6 +37,9 @@ class CpuPlatform(Platform):
                              use_mla: bool) -> str:
         if selected_backend and selected_backend != _Backend.TORCH_SDPA:
             logger.info("Cannot use %s backend on CPU.", selected_backend)
+        if use_mla:
+            logger.info("Using CPU MLA backend.")
+            return "vllm.attention.backends.cpu_mla.CPUMLABackend"
         logger.info("Using Torch SDPA backend.")
         return "vllm.attention.backends.torch_sdpa.TorchSDPABackend"
 
@@ -129,9 +132,6 @@ class CpuPlatform(Platform):
         # Disable torch async compiling which won't work with daemonic processes
         os.environ["TORCHINDUCTOR_COMPILE_THREADS"] = "1"
 
-        # MLA attention is not supported
-        os.environ["VLLM_MLA_DISABLE"] = "1"
-
         # Intel OpenMP setting
         ld_prealod_str = os.getenv("LD_PRELOAD", "")
         if "libiomp5.so" in ld_prealod_str:

vllm/worker/cpu_model_runner.py

@@ -469,6 +469,7 @@ class CPUModelRunnerBase(ModelRunnerBase[TModelInputForCPU]):
             self.kv_cache_dtype,
             self.block_size,
             self.model_config.is_attention_free,
+            use_mla=self.model_config.use_mla,
         ) if needs_attn_backend else None
 
         # Multi-modal data support

vllm/worker/cpu_worker.py

@@ -66,6 +66,7 @@ class CPUCacheEngine:
             cache_config.cache_dtype,
             self.block_size,
             self.model_config.is_attention_free,
+            use_mla=self.model_config.use_mla,
         )
 
         # Initialize the cache.