remove warpSize usage on host side

Author: jeffdaily

aten/src/ATen/native/cuda/SoftMax.cu

@@ -177,15 +177,16 @@ inline dim3 SoftMaxForward_getBlockSize(uint64_t dim_size) {
   uint64_t block_size = 1;
   uint64_t max_block_size = std::min(dim_size, static_cast<uint64_t>(max_threads));
 
-  // We need a block size that is a multiple of C10_WARP_SIZE in order
+  // We need a block size that is a multiple of at::cuda::warp_size() in order
   // to perform block size reductions using warp shuffle instructions.
   // Since max_threads is also a multiple of C10_WARPS_SIZE we do not
   // risk creating a block size larger than the limit.
 
-  if (max_block_size % C10_WARP_SIZE == 0) {
+  int warp_size = at::cuda::warp_size();
+  if (max_block_size % warp_size == 0) {
     block_size = max_block_size;
   } else {
-    block_size = (max_block_size / C10_WARP_SIZE + 1) * C10_WARP_SIZE;
+    block_size = (max_block_size / warp_size + 1) * warp_size;
   }
 
   return dim3(block_size);
@@ -978,7 +979,7 @@ Tensor host_softmax(const Tensor & input_, const int64_t dim_, const bool half_t
           } else {
             constexpr int ILP = sizeof(float4) / sizeof(scalar_t);
             dim3 block = SoftMaxForward_getBlockSize(dim_size);
-            size_t smem_reduction_sz = block.x / C10_WARP_SIZE * sizeof(accscalar_t);
+            size_t smem_reduction_sz = block.x / at::cuda::warp_size() * sizeof(accscalar_t);
             auto max_elements_per_smem = (at::cuda::getCurrentDeviceProperties()->sharedMemPerBlock -
               smem_reduction_sz) / sizeof(scalar_t);
 
@@ -1057,7 +1058,7 @@ Tensor host_softmax(const Tensor & input_, const int64_t dim_, const bool half_t
           } else {
             constexpr int ILP = sizeof(float4) / sizeof(scalar_t);
             dim3 block = SoftMaxForward_getBlockSize(dim_size);
-            size_t smem_reduction_sz = block.x / C10_WARP_SIZE * sizeof(accscalar_t);
+            size_t smem_reduction_sz = block.x / at::cuda::warp_size() * sizeof(accscalar_t);
             auto max_elements_per_smem = (at::cuda::getCurrentDeviceProperties()->sharedMemPerBlock -
               smem_reduction_sz) / sizeof(scalar_t);
 
@@ -1122,7 +1123,7 @@ void dispatch_host_softmax_backward(int64_t dim_size, dim3 grid, Tensor &grad, T
   constexpr int ILP = sizeof(float4) / sizeof(output_t);
   dim3 block = SoftMax_getBlockSize(ILP, dim_size);
 
-  size_t smem_reduction_sz = block.x / C10_WARP_SIZE * sizeof(accscalar_t);
+  size_t smem_reduction_sz = block.x / at::cuda::warp_size() * sizeof(accscalar_t);
   auto max_elements_per_smem = (at::cuda::getCurrentDeviceProperties()->sharedMemPerBlock -
     smem_reduction_sz) / sizeof(output_t);
   bool can_use_smem = static_cast<size_t>(dim_size) < max_elements_per_smem;

aten/src/ATen/native/cuda/TensorTopK.cu

@@ -439,8 +439,12 @@ __global__ void computeBlockwiseWithinKCounts(
     warp_counts[warp] = count;
   }
   __syncthreads();
+#ifdef USE_ROCM
+  CUDA_KERNEL_ASSERT(RADIX_DIGITS < C10_WARP_SIZE * C10_WARP_SIZE);
+#else
   static_assert(RADIX_DIGITS < C10_WARP_SIZE * C10_WARP_SIZE,
     "Assuming only 1 warp is needed for final reduction");
+#endif
   if (warp != 0) {
     return;
   }

aten/src/ATen/native/cuda/block_reduce.cuh

@@ -12,7 +12,13 @@ constexpr int kCUDABlockReduceNumThreads = 512;
 // of which reduces C10_WARP_SIZE elements. So, at most
 // C10_WARP_SIZE**2 elements can be reduced at a time.
 // NOTE: This is >= the max block size on current hardware anyway (1024).
+// ROCm NOTE: C10_WARP_SIZE should only be used inside device functions,
+// and kCUDABlockReduceMaxThreads is a host-side variable.
+#ifdef USE_ROCM
+static const int kCUDABlockReduceMaxThreads = at::cuda::warp_size() * at::cuda::warp_size();
+#else
 constexpr int kCUDABlockReduceMaxThreads = C10_WARP_SIZE * C10_WARP_SIZE;
+#endif
 
 // Sums `val` across all threads in a warp.
 //

c10/macros/Macros.h

@@ -312,7 +312,21 @@ constexpr uint32_t CUDA_THREADS_PER_BLOCK_FALLBACK = 256;
 #endif
 
 #if defined(USE_ROCM)
-#define C10_WARP_SIZE warpSize // = 64 or 32 (Defined in hip_runtime.h)
+// C10_WARP_SIZE is only allowed for device code.
+// Host code _must_ use at::cuda::warp_size()
+// HIP header used to define warpSize as a constexpr that was either 32 or 64
+// depending on the target device, and then always set it to 64 for host code.
+// Host pass of HIP compiler needs C10_WARP_SIZE defined to _something_ so we
+// set it to something unreasonable to trigger obvious host code errors.
+#if defined(__HIP_DEVICE_COMPILE__)
+#if defined(__GFX9__)
+static constexpr int C10_WARP_SIZE = 64;
+#else // __GFX9__
+static constexpr int C10_WARP_SIZE = 32;
+#endif // __GFX9__
+#else
+static constexpr int C10_WARP_SIZE = 1;
+#endif // __HIP_DEVICE_COMPILE__
 #else
 #define C10_WARP_SIZE 32
 #endif

third_party/composable_kernel

@@ -471,7 +471,7 @@ static __global__ void barrier_kernel(
 void CUDASymmetricMemory::barrier(int channel, size_t timeout_ms) {
   check_channel(channel, world_size_);
   c10::cuda::CUDAGuard guard(local_device_idx_);
-  barrier_kernel<<<1, C10_WARP_SIZE, 0, at::cuda::getCurrentCUDAStream()>>>(
+  barrier_kernel<<<1, at::cuda::warp_size(), 0, at::cuda::getCurrentCUDAStream()>>>(
       reinterpret_cast<uint32_t**>(signal_pads_dev_),
       channel,
       rank_,
@@ -509,7 +509,7 @@ void CUDASymmetricMemory::put_signal(
     size_t timeout_ms) {
   check_channel(channel, world_size_);
   c10::cuda::CUDAGuard guard(local_device_idx_);
-  put_signal_kernel<<<1, C10_WARP_SIZE, 0, at::cuda::getCurrentCUDAStream()>>>(
+  put_signal_kernel<<<1, at::cuda::warp_size(), 0, at::cuda::getCurrentCUDAStream()>>>(
       reinterpret_cast<uint32_t**>(signal_pads_dev_),
       dst_rank,
       channel,
@@ -553,7 +553,7 @@ void CUDASymmetricMemory::wait_signal(
     size_t timeout_ms) {
   check_channel(channel, world_size_);
   c10::cuda::CUDAGuard guard(local_device_idx_);
-  wait_signal_kernel<<<1, C10_WARP_SIZE, 0, at::cuda::getCurrentCUDAStream()>>>(
+  wait_signal_kernel<<<1, at::cuda::warp_size(), 0, at::cuda::getCurrentCUDAStream()>>>(
       reinterpret_cast<uint32_t**>(signal_pads_dev_),
       src_rank,
       channel,

torch/csrc/distributed/c10d/CUDASymmetricMemory.cu

@@ -104,7 +104,7 @@ void init_elementwise_launch_config(
     num_blocks = 1;
     num_threads = at::round_up(
         at::ceil_div(numel_per_split, numel_per_thread),
-        static_cast<size_t>(C10_WARP_SIZE));
+        static_cast<size_t>(at::cuda::warp_size()));
   } else {
     num_blocks = std::min(
         at::ceil_div(numel_per_split, max_num_threads * numel_per_thread),