[CUDA] cuDNN Flash Attention (#21629)

### Description
- [x] Add cuDNN flash attention using cudnn frontend, and enable it in
MultiHeadAttention operator.
- [x] Support attention mask.
- [x] Support attention bias.
- [x] Update tests and benchmark script.

The cuDNN SDPA is disabled by default. To enable it, need the following:
(1) Requires cuDNN 9.3 or newer version installed.
(2) Set an environment variable `ORT_ENABLE_CUDNN_FLASH_ATTENTION=1` or
set `sdpa_kernel=8` cuda provider option to enable it.
(3) Only works on devices with compute capability >= 8.0.

Note that some combinations of parameters might be rejected due to
limited support of head dimension or sequence lengths.

Future Works:
(1) FP8 and BF16 APIs.  Currently, only API for FP16 are exposed.
(2) Add API to support ragged batching (padding removed in inputs).
(3) Support other input formats (like QKV_BS3NH).
(4) Currently, q are converted to BSNH, k/v are converted to either BSNH
or BNSH format. May do some experiment to see whether converting q to
BNSH could be better in some case.

### Example Benchmark Results on H100

The following tests are on FP16 MultiHeadAttention operator without
attention mask and attention bias.

#### Test Setting 1
batch_size | sequence_length | past_sequence_length | num_heads |
head_size
-- | -- | -- | -- | --
16 | 256 | 0 | 32 | 128

format | average_latency | tflops | kernel
-- | -- | -- | --
Q,K,V (BNSH) | 0.000075 | 229.5 | torch:flash
Q,K,V (BNSH) | 0.000119 | 144.8 | torch:efficient
Q,K,V (BNSH) | 0.000224 | 76.5 | torch:math
Q,K,V (BSNH) | 0.000075 | 227.8 | ort:cudnn
Q,K,V (BSNH) | 0.000094 | 182.8 | ort:flash
Q,K,V (BSNH) | 0.000138 | 124.7 | ort:efficient
Q,K,V (BSNH) | 0.000438 | 39.3 | ort:math
Q,KV | 0.000129 | 133.0 | ort:cudnn
Q,KV | 0.000151 | 114.1 | ort:flash
Q,KV | 0.000194 | 88.5 | ort:efficient
QKV | 0.000154 | 111.8 | ort:cudnn
QKV | 0.000175 | 98.0 | ort:flash
QKV | 0.000217 | 79.0 | ort:efficient

#### Test Setting 2

batch_size | sequence_length | past_sequence_length | num_heads |
head_size
-- | -- | -- | -- | --
16 | 512 | 0 | 16 | 64

format | average_latency | tflops | kernel
-- | -- | -- | --
Q,K,V (BNSH) | 0.000069 | 249.2 | torch:flash
Q,K,V (BNSH) | 0.000141 | 121.7 | torch:efficient
Q,K,V (BNSH) | 0.000294 | 58.5 | torch:math
Q,K,V (BSNH) | 0.000077 | 221.7 | ort:cudnn
Q,K,V (BSNH)  | 0.000087 | 196.6 | ort:flash
Q,K,V (BSNH)  | 0.000163 | 105.6 | ort:efficient
Q,K,V (BSNH)  | 0.000651 | 26.4 | ort:math
Q,KV | 0.000103 | 167.1 | ort:cudnn
Q,KV | 0.000117 | 146.3 | ort:flash
Q,KV | 0.000192 | 89.6 | ort:efficient
QKV | 0.000113 | 151.5 | ort:cudnn
QKV | 0.000128 | 134.7 | ort:flash
QKV | 0.000201 | 85.3 | ort:efficient

cmake/external/cuDNN.cmake

@@ -107,5 +107,3 @@ elseif(CUDNN_MAJOR_VERSION EQUAL 9)
         CUDNN::cudnn_heuristic
     )
 endif()
-
-mark_as_advanced(CUDNN_INCLUDE_DIR)

cmake/onnxruntime_rocm_hipify.cmake

@@ -5,6 +5,7 @@ find_package(Python3 COMPONENTS Interpreter REQUIRED)
 
 # GLOB pattern of file to be excluded
 set(contrib_ops_excluded_files
+  "bert/cudnn_fmha/*"
   "bert/cutlass_fmha/*"
   "bert/fastertransformer_decoder_attention/*"
   "bert/flash_attention/*"

onnxruntime/contrib_ops/cpu/bert/attention_common.h

@@ -47,6 +47,7 @@ enum AttentionKernelType {
   AttentionKernel_TrtFusedCrossAttention,
   AttentionKernel_CutlassMemoryEfficientAttention,
   AttentionKernel_FlashAttention,
+  AttentionKernel_CudnnFlashAttention,
   AttentionKernel_Default
 };
 

onnxruntime/contrib_ops/cuda/bert/attention.cc

@@ -246,6 +246,7 @@ Status Attention<T>::ComputeInternal(OpKernelContext* context) const {
 
   constexpr size_t element_size = sizeof(T);
   constexpr bool use_fused_cross_attention = false;
+  constexpr bool use_cudnn_flash_attention = false;
   size_t workSpaceSize = GetAttentionWorkspaceSize(element_size,
                                                    parameters.batch_size,
                                                    parameters.num_heads,
@@ -258,6 +259,7 @@ Status Attention<T>::ComputeInternal(OpKernelContext* context) const {
                                                    use_flash_attention,
                                                    use_fused_cross_attention,
                                                    use_memory_efficient_attention,
+                                                   use_cudnn_flash_attention,
                                                    false);
   IAllocatorUniquePtr<void> work_space = IAllocator::MakeUniquePtr<void>(allocator, workSpaceSize, false, context->GetComputeStream());
 
@@ -294,7 +296,8 @@ Status Attention<T>::ComputeInternal(OpKernelContext* context) const {
     data.out_accum = reinterpret_cast<CudaT*>(out_accum_buffer.get());
   }
 
-  return QkvToContext<CudaT>(device_prop, cublas, context->GetComputeStream(), parameters, data);
+  cudnnHandle_t cudnn = GetCudnnHandle(context);
+  return QkvToContext<CudaT>(device_prop, cublas, cudnn, context->GetComputeStream(), parameters, data);
 }
 
 }  // namespace cuda

onnxruntime/contrib_ops/cuda/bert/attention_impl.cu

@@ -37,6 +37,7 @@ limitations under the License.
 #include "contrib_ops/cuda/bert/bert_padding.h"
 #include "contrib_ops/cuda/utils/dump_cuda_tensor.h"
 #include "contrib_ops/cuda/bert/cutlass_fmha/memory_efficient_attention.h"
+#include "contrib_ops/cuda/bert/cudnn_fmha/cudnn_flash_attention.h"
 #include "contrib_ops/cuda/bert/flash_attention/flash_api.h"
 #include "contrib_ops/cuda/bert/attention_impl.h"
 
@@ -109,6 +110,7 @@ size_t GetAttentionWorkspaceSize(
     bool use_flash_attention,
     bool use_fused_cross_attention,
     bool use_memory_efficient_attention,
+    bool use_cudnn_flash_attention,
     bool no_qkv_workspace) {
   // Note that q, k and v might need alignment for fused attention kernels.
   const size_t qkv_size = element_size * batch_size * num_heads *
@@ -144,6 +146,10 @@ size_t GetAttentionWorkspaceSize(
     return qkv_bytes + 2 * GetSequenceOffsetSize(static_cast<int>(batch_size), true);
   }
 
+  if (use_cudnn_flash_attention) {
+    return qkv_bytes;
+  }
+
   return qkv_bytes + 2 * GetAttentionScratchSize(element_size, batch_size, num_heads, sequence_length,
                                                  total_sequence_length);
 }
@@ -320,6 +326,68 @@ Status FlashAttention(
 }
 #endif
 
+template <typename T>
+Status CudnnFlashAttention(
+    cudnnHandle_t cudnn_handle,
+    Stream* ort_stream,
+    contrib::AttentionParameters& parameters,
+    AttentionData<T>& data,
+    float scale) {
+  assert(data.qkv_format == AttentionQkvFormat::Q_K_V_BSNH ||
+         data.qkv_format == AttentionQkvFormat::Q_K_V_BSNH_BNSH_BNSH ||
+         data.qkv_format == AttentionQkvFormat::Q_K_V_BNSH);
+  assert(parameters.mask_type == AttentionMaskType::MASK_NONE ||
+         parameters.mask_type == AttentionMaskType::MASK_1D_KEY_SEQ_LEN);
+  constexpr bool is_bf16 = false;
+
+  T* attention_bias = const_cast<T*>(data.attention_bias);
+  int* mask_sequence_lengths_kv = const_cast<int*>(data.mask_index);
+
+  cudnn_sdpa::run(
+      data.output,
+      data.q,
+      data.k,
+      data.v,
+      attention_bias,
+      nullptr,                                 // (optional) mask_sequence_lengths_q
+      mask_sequence_lengths_kv,                // (optional) mask_sequence_lengths_kv
+      parameters.batch_size,
+      parameters.num_heads,                    // num_heads_q,
+      parameters.num_heads,                    // num_heads_kv,
+      parameters.head_size,                    // head_size_qk
+      parameters.v_head_size,                  // head_size_v
+      parameters.sequence_length,              // sequence_length_q
+      parameters.total_sequence_length,        // sequence_length_kv
+      scale,                                   // scaling factor applied prior softmax
+      parameters.is_unidirectional,            // causal
+      is_bf16,                                 // True if bfloat16, otherwise float16
+      parameters.broadcast_attn_bias_dim_0,    // broadcast attention bias dimension 0 or not
+      parameters.broadcast_attn_bias_dim_1,    // broadcast attention bias dimension 1 or not
+      0,                                       // sliding window length. 0 means no sliding window.
+      data.qkv_format,
+      cudnn_handle,
+      ort_stream,
+      data.allocator);
+
+  return Status::OK();
+}
+
+template <>
+Status CudnnFlashAttention(
+    cudnnHandle_t cudnn_handle,
+    Stream* ort_stream,
+    contrib::AttentionParameters& parameters,
+    AttentionData<float>& data,
+    float scale) {
+  ORT_UNUSED_PARAMETER(cudnn_handle);
+  ORT_UNUSED_PARAMETER(ort_stream);
+  ORT_UNUSED_PARAMETER(parameters);
+  ORT_UNUSED_PARAMETER(data);
+  ORT_UNUSED_PARAMETER(scale);
+  return ORT_MAKE_STATUS(ONNXRUNTIME, StatusCode::NOT_IMPLEMENTED,
+                         "cudnn flash attention does not support float tensor");
+}
+
 #if USE_MEMORY_EFFICIENT_ATTENTION
 template <typename T>
 Status EfficientAttention(
@@ -498,6 +566,7 @@ template <typename T>
 Status QkvToContext(
     const cudaDeviceProp& device_prop,
     cublasHandle_t& cublas,
+    cudnnHandle_t& cudnn,
     Stream* ort_stream,
     contrib::AttentionParameters& parameters,
     AttentionData<T>& data) {
@@ -512,10 +581,11 @@ Status QkvToContext(
   void* fused_runner = data.fused_runner;
 
   // At most one fused kernel is enabled.
-  assert((int(data.use_flash_attention) +
-          int(data.use_memory_efficient_attention) +
-          int(fused_runner != nullptr) +
-          int(data.fused_cross_attention_kernel != nullptr)) <= 1);
+  assert((static_cast<int>(data.use_flash_attention) +
+          static_cast<int>(data.use_memory_efficient_attention) +
+          static_cast<int>(fused_runner != nullptr) +
+          static_cast<int>(data.fused_cross_attention_kernel != nullptr) +
+          static_cast<int>(data.kernel_type == AttentionKernelType::AttentionKernel_CudnnFlashAttention)) <= 1);
 
   ORT_RETURN_IF_ERROR(PrepareQkv<T>(parameters, data, stream, max_threads_per_block));
 
@@ -577,6 +647,10 @@ Status QkvToContext(
   }
 #endif
 
+  if (data.kernel_type == AttentionKernelType::AttentionKernel_CudnnFlashAttention) {
+    return CudnnFlashAttention(cudnn, ort_stream, parameters, data, scale);
+  }
+
 #if USE_MEMORY_EFFICIENT_ATTENTION
   if (data.use_memory_efficient_attention) {
     return EfficientAttention(device_prop, stream, parameters, data, scale);
@@ -594,13 +668,15 @@ template struct AttentionData<half>;
 template Status QkvToContext<float>(
     const cudaDeviceProp& device_prop,
     cublasHandle_t& cublas,
+    cudnnHandle_t& cudnn,
     Stream* ort_stream,
     contrib::AttentionParameters& parameters,
     AttentionData<float>& data);
 
 template Status QkvToContext<half>(
     const cudaDeviceProp& device_prop,
     cublasHandle_t& cublas,
+    cudnnHandle_t& cudnn,
     Stream* ort_stream,
     contrib::AttentionParameters& parameters,
     AttentionData<half>& data);

onnxruntime/contrib_ops/cuda/bert/attention_impl.h

@@ -9,6 +9,7 @@
 #include <iostream>
 #include <mutex>
 #include "core/framework/allocator.h"
+#include "core/providers/cuda/cuda_common.h"
 #include "contrib_ops/cpu/bert/attention_common.h"
 
 namespace onnxruntime {
@@ -54,6 +55,7 @@ size_t GetAttentionWorkspaceSize(
     bool use_flash_attention,
     bool use_fused_cross_attention,
     bool use_memory_efficient_attention,
+    bool use_cudnn_flash_attention,
     bool no_qkv_workspace);
 
 template <typename T>
@@ -104,9 +106,11 @@ struct AttentionData {
   size_t workspace_bytes = 0;
   bool allow_debug_info = false;
 
+  // For MultiHeadAttention only.
+  AttentionKernelType kernel_type = AttentionKernelType::AttentionKernel_Default;
+  AllocatorPtr allocator = nullptr;
   bool IsUnfused() const {
-    return !use_flash_attention && !use_memory_efficient_attention &&
-           (fused_runner == nullptr) && (fused_cross_attention_kernel == nullptr);
+    return kernel_type == AttentionKernelType::AttentionKernel_Unfused;
   }
 
   void PrintDebugInfo() const {
@@ -139,6 +143,7 @@ template <typename T>
 Status QkvToContext(
     const cudaDeviceProp& device_prop,
     cublasHandle_t& cublas,
+    cudnnHandle_t& cudnn,
     Stream* stream,
     contrib::AttentionParameters& parameters,
     AttentionData<T>& data);

onnxruntime/contrib_ops/cuda/bert/attention_kernel_options.cc

@@ -9,11 +9,12 @@
 #include "core/providers/shared_library/provider_api.h"
 #include "core/platform/env_var_utils.h"
 #include "contrib_ops/cuda/bert/tensorrt_fused_multihead_attention/mha_runner.h"
+#include "contrib_ops/cuda/bert/cudnn_fmha/cudnn_flash_attention.h"
 
 using namespace onnxruntime::contrib::attention;
 
 namespace onnxruntime {
-void AttentionKernelOptions::Initialize(int value, bool use_build_flag) {
+void AttentionKernelOptions::Initialize(int value, bool use_build_flag, bool check_cudnn_version) {
   if (value > 0) {
     use_flash_attention_ = (value & static_cast<int>(AttentionBackend::FLASH_ATTENTION)) > 0;
     use_efficient_attention_ = (value & static_cast<int>(AttentionBackend::EFFICIENT_ATTENTION)) > 0;
@@ -28,6 +29,7 @@ void AttentionKernelOptions::Initialize(int value, bool use_build_flag) {
     use_efficient_attention_ = !ParseEnvironmentVariableWithDefault<bool>(kDisableMemoryEfficientAttention, false);
     use_trt_fused_attention_ = !ParseEnvironmentVariableWithDefault<bool>(kDisableFusedSelfAttention, false);
     use_cudnn_flash_attention_ = ParseEnvironmentVariableWithDefault<bool>(kEnableCudnnFlashAttention, false);
+
     use_unfused_ = true;
     use_trt_flash_attention_ = !ParseEnvironmentVariableWithDefault<bool>(kDisableTrtFlashAttention, false);
     use_trt_cross_attention_ = !ParseEnvironmentVariableWithDefault<bool>(kDisableFusedCrossAttention, false);
@@ -45,6 +47,14 @@ void AttentionKernelOptions::Initialize(int value, bool use_build_flag) {
       kMinSeqLenForEfficientAttentionFp32,
       value > 0 ? 0 : kDefaultMinSeqLenForEfficientAttentionFp32);
 
+  // Enable cuDNN flash attention only when it is stable (requires cuDNN version >= 9.3.0).
+  if (use_cudnn_flash_attention_ && check_cudnn_version && !::onnxruntime::cudnn_sdpa::is_stable()) {
+    use_cudnn_flash_attention_ = false;
+    if (enable_kernel_debug_info_) {
+      std::cout << "cuDNN Flash Attention is disabled. Requires cuDNN 9.3 or later." << std::endl;
+    }
+  }
+
   if (use_build_flag) {
     // Some kernels can be disabled at build time. If they are disabled, we should not use them.
 #ifndef USE_FLASH_ATTENTION
@@ -58,9 +68,9 @@ void AttentionKernelOptions::Initialize(int value, bool use_build_flag) {
 }
 
 void AttentionKernelOptions::InitializeOnce(
-    int sdpa_kernel, bool use_build_flag) {
+    int sdpa_kernel, bool use_build_flag, bool check_cudnn_version) {
   std::call_once(this->initialize_once_flag_, [&]() {
-    this->Initialize(sdpa_kernel, use_build_flag);
+    this->Initialize(sdpa_kernel, use_build_flag, check_cudnn_version);
     if (this->enable_kernel_debug_info_) {
       this->Print();
     }

onnxruntime/contrib_ops/cuda/bert/attention_kernel_options.h

@@ -21,7 +21,7 @@ struct AttentionKernelDebugInfo {
 
 class AttentionKernelOptions {
  public:
-  void InitializeOnce(int sdpa_kernel, bool use_build_flag);
+  void InitializeOnce(int sdpa_kernel, bool use_build_flag, bool check_cudnn_version = false);
 
   bool UseFlashAttention() const { return use_flash_attention_; }
   bool UseEfficientAttention() const { return use_efficient_attention_; }
@@ -40,7 +40,7 @@ class AttentionKernelOptions {
  protected:
   void Print() const;
 
-  void Initialize(int value, bool use_build_flag);
+  void Initialize(int value, bool use_build_flag, bool check_cudnn_version);
 
  private:
   bool use_flash_attention_{true};