Reworked multi tensor apply, added tests

apex/amp/__init__.py

@@ -2,4 +2,3 @@ from .amp import init, half_function, float_function, promote_function,\
     register_half_function, register_float_function, register_promote_function
 from .handle import scale_loss
 from .frontend import register
-from .multi_tensor_apply import MultiTensorApply, multi_tensor_applier

apex/amp/initialize.py → apex/amp/_initialize.py

@@ -11,14 +11,14 @@ def check_params_fp32(model):
     for name, param in model.named_parameters():
         if param.is_floating_point() and param.type() != "torch.cuda.FloatTensor":
             print("Warning:  Found param {} with type {}, expected torch.cuda.FloatTensor.\n"
-                  "When using amp.register, you do not need to call .half() on your model\n"
+                  "When using amp.initialize, you do not need to call .half() on your model\n"
                   "before passing it, no matter what optimization level you choose.".format(
                   name, param.type()))
 
     for name, buf in model.named_buffers():
         if buf.is_floating_point() and buf.type() != "torch.cuda.FloatTensor":
             print("Warning:  Found buffer {} with type {}, expected torch.cuda.FloatTensor.\n"
-                  "When using amp.register, you do not need to call .half() on your model\n"
+                  "When using amp.initialize, you do not need to call .half() on your model\n"
                   "before passing it, no matter what optimization level you choose.".format(
                   name, buf.type()))
 
@@ -79,7 +79,7 @@ def _initialize(models, optimizers, properties):
         if parallel_type is not None:
             raise RuntimeError("Incoming model is an instance of {}. ".format(parallel_type) +
                 "Parallel wrappers should only be applied AFTER the model(s) have been "
-                "returned from amp.register.")
+                "returned from amp.initialize.")
 
     for model in models:
         check_params_fp32(model)

apex/amp/frontend.py

 import torch
-from .initialize import _initialize
+from ._initialize import _initialize
 from ._amp_state import _amp_state
 
 
@@ -24,7 +24,7 @@ class Properties(object):
             "enable_ddp_interop" : False}
 
     """
-    This function will allow updating several options at a time without routing through
+    This function allows updating several options at a time without routing through
     __setattr__ checks, to avoid "you can't get there from here" scenarios.
     """
     def update_options_dict(new_options):
@@ -97,7 +97,7 @@ class O2:
         properties.cast_torch_functions = False
         properties.cast_batchnorm = torch.float32
         properties.master_weights = True
-        properties.loss_scale = 128.0
+        properties.loss_scale = "dynamic"
         properties.flatten_model_params = False
         properties.flatten_master_params = False
         properties.fused_optimizer = False
@@ -160,20 +160,20 @@ def check_params_fp32(model):
     for name, param in model.named_parameters():
         if param.type() != "torch.cuda.FloatTensor":
             print("Warning:  Found param {} with type {}, expected torch.cuda.FloatTensor.\n"
-                  "When using amp.register, you do not need to call .half() on your model\n"
+                  "When using amp.initialize, you do not need to call .half() on your model\n"
                   "before passing it, no matter what optimization level you choose.",
                   name, param.type())
 
     for name, param in model.named_buffers():
         if param.type() != "torch.cuda.FloatTensor":
             print("Warning:  Found buffer {} with type {}, expected torch.cuda.FloatTensor.\n"
-                  "When using amp.register, you do not need to call .half() on your model\n"
+                  "When using amp.initialize, you do not need to call .half() on your model\n"
                   "before passing it, no matter what optimization level you choose.",
                   name, param.type())
 
 
 # allow user to directly pass Properties struct as well?
-def register(models, optimizers, enabled=True, opt_level=None, **kwargs):
+def initialize(models, optimizers, enabled=True, opt_level=None, **kwargs):
     """
     Expected kwargs:
     opt_level=None,

apex/amp/multi_tensor_apply.py

-import torch
-
-class MultiTensorApply(object):
-    available = False
-    warned = False
-
-    def __init__(self, max_blocks, max_tensors, max_depth, chunk_size):
-        try:
-            import amp_C
-            MultiTensorApply.available = True
-            MultiTensorApply.prep_multi_tensor_launch = amp_C.prep_multi_tensor_launch
-            self.chunk_size = chunk_size
-            self.reallocate(max_blocks, max_tensors, max_depth)
-        except ImportError as err:
-            MultiTensorApply.availble = False
-            MultiTensorApply.import_err = err
-
-    def check_avail(self):
-        if MultiTensorApply.available == False:
-            raise RuntimeError(
-                "Attempted to call MultiTensorApply method, but MultiTensorApply "
-                "is not available, possibly because Apex was installed without "
-                "--cpp_ext --cuda_ext.  Original import error message:",
-                MultiTensorApply.import_err)
-
-    def __call__(self, op, noop_flag_buffer, tensor_lists, *args):
-        self.check_avail()
-
-        assert len(tensor_lists) > 0, "len(tensor_lists) = {}".format(len(tensor_lists))
-        len0 = len(tensor_lists[0])
-        assert len0 > 0, "len(tensor_lists[0]) = {}".format(len0)
-        for i, l in enumerate(tensor_lists):
-            assert len(tensor_lists[i]) == len0,\
-                "len(tensor_lists[{}] = {}, len(tensor_lists[0] = {}".format(
-                len(tensor_lists[i]), len(tensor_lists[0]))
-
-        self.assign_blocks(tensor_lists)
-        # print(self.gpu_block_to_tensor)
-        # print(self.gpu_block_to_chunk)
-        # print(self.gpu_tensor_sizes)
-
-        return op(self.nblocks,
-                  noop_flag_buffer,
-                  self.cpu_tensor_addresses,
-                  self.gpu_block_to_tensor,
-                  self.gpu_block_to_chunk,
-                  self.gpu_tensor_sizes,
-                  self.gpu_tensor_addresses,
-                  self.chunk_size,
-                  tensor_lists,
-                  *args)
-
-        # print()
-        # print([[p.data_ptr() for p in l] for l in tensor_lists])
-        # print()
-        # print(self.gpu_tensor_addresses)
-
-    def assign_blocks(self, tensor_lists):
-        self.check_avail()
-
-        needs_reallocate = False
-
-        # Currently, this loop appears prohibitively expensive.
-        # Need to move to c++.
-        torch.cuda.nvtx.range_push("assign_blocks loop")
-        # list0 = tensor_lists[0]
-        # self.nblocks = 0
-        # for t, tensor in enumerate(list0):
-        #     blocks_this_tensor = (tensor.numel() +
-        #                           self.chunk_size - 1)//self.chunk_size
-        #     if not needs_reallocate:
-        #         self.cpu_tensor_sizes[t] = tensor.numel()
-        #     for chunk in range(blocks_this_tensor):
-        #         if self.nblocks >= self.max_blocks:
-        #             needs_reallocate = True
-        #         if not needs_reallocate:
-        #             self.cpu_block_to_tensor[self.nblocks] = t
-        #             self.cpu_block_to_chunk[self.nblocks] = chunk
-        #         self.nblocks += 1
-        needs_reallocate, self.nblocks = MultiTensorApply.prep_multi_tensor_launch(
-            self.cpu_block_to_tensor,
-            self.cpu_block_to_chunk,
-            self.cpu_tensor_sizes,
-            self.gpu_block_to_tensor,
-            self.gpu_block_to_chunk,
-            self.gpu_tensor_sizes,
-            self.chunk_size,
-            self.max_depth,
-            self.max_tensors,
-            self.max_blocks,
-            tensor_lists)
-        torch.cuda.nvtx.range_pop()
-
-        # print(self.nblocks)
-
-        if self.nblocks > self.max_blocks:
-            self.max_blocks = self.nblocks
-        if len(tensor_lists) > self.max_depth:
-            self.max_depth = len(tensor_lists)
-        if len(tensor_lists[0]) > self.max_tensors:
-            self.max_tensors = len(tensor_lists[0])
-
-        if needs_reallocate:
-            self.reallocate(self.max_blocks, self.max_tensors, self.max_depth)
-            needs_reallocate, self.nblocks = MultiTensorApply.prep_multi_tensor_launch(
-                self.cpu_block_to_tensor,
-                self.cpu_block_to_chunk,
-                self.cpu_tensor_sizes,
-                self.gpu_block_to_tensor,
-                self.gpu_block_to_chunk,
-                self.gpu_tensor_sizes,
-                self.chunk_size,
-                self.max_depth,
-                self.max_tensors,
-                self.max_blocks,
-                tensor_lists)
-            assert needs_reallocate == 0, "Should not need reallocate on second attempt."
-            assert self.nblocks <= self.max_blocks, "Should not need to increase blocks again."
-
-    def reallocate(self, max_blocks, max_tensors, max_depth):
-        self.check_avail()
-
-        self.max_blocks = max_blocks
-        self.max_tensors = max_tensors
-        self.max_depth = max_depth
-
-        self.cpu_block_to_tensor = torch.IntTensor(max_blocks).pin_memory()
-        self.cpu_block_to_chunk = torch.IntTensor(max_blocks).pin_memory()
-        self.cpu_tensor_sizes = torch.IntTensor(max_tensors).pin_memory()
-        self.cpu_tensor_addresses = torch.LongTensor(max_depth, max_tensors).pin_memory()
-
-        self.gpu_block_to_tensor = torch.cuda.IntTensor(max_blocks)
-        self.gpu_block_to_chunk = torch.cuda.IntTensor(max_blocks)
-        self.gpu_tensor_sizes = torch.cuda.IntTensor(max_tensors)
-        self.gpu_tensor_addresses = torch.cuda.LongTensor(max_depth, max_tensors)
-
-multi_tensor_applier = MultiTensorApply(1000, 100, 4, 2048)

apex/amp/scaler.py

 import torch
 import logging
-from .multi_tensor_apply import multi_tensor_applier
+from ..multi_tensor_apply import multi_tensor_applier
 from ._amp_state import _amp_state
 
 # from apex_C import scale_check_overflow
@@ -46,7 +46,7 @@ class LossScaler(object):
         if multi_tensor_applier.available:
             import amp_C
             LossScaler.has_fused_kernel = multi_tensor_applier.available
-            LossScaler.multi_tensor_unscale_cuda = amp_C.multi_tensor_unscale
+            LossScaler.multi_tensor_scale_cuda = amp_C.multi_tensor_scale
         else:
             if not LossScaler.warned_no_fused_kernel:
                 print("Warning:  multi_tensor_applier fused downscale kernel is unavailable, "
@@ -115,7 +115,7 @@ class LossScaler(object):
                     return
                 else:
                     multi_tensor_applier(
-                        LossScaler.multi_tensor_unscale_cuda,
+                        LossScaler.multi_tensor_scale_cuda,
                         self._overflow_buf,
                         [model_grads, master_grads],
                         1./scale)

apex/fp16_utils/fp16_optimizer.py

@@ -515,15 +515,24 @@ class FP16_Optimizer(object):
         # self._downscale_master()
         # Use the one-shot multi-tensor apply kernel
         if len(self.all_fp16_params) > 0:
+            # print("Model grads before")
+            # print([param.grad.data for param in self.all_fp16_params])
             self.loss_scaler.unscale(
                 self.all_fp16_params,
                 self.all_fp32_from_fp16_params,
                 self.loss_scaler.loss_scale())
+            # print("Master grads after")
+            # print([param.grad.data for param in self.all_fp32_from_fp16_params])
         if len(self.all_fp32_from_fp32_params) > 0:
+            # print("Model grads before")
+            # print([param.grad.data for param in self.all_fp32_from_fp32_params])
             self.loss_scaler.unscale(
                 self.all_fp32_from_fp32_params,
                 self.all_fp32_from_fp32_params,
                 self.loss_scaler.loss_scale())
+            # print("Master grads after")
+            # print([param.grad.data for param in self.all_fp32_from_fp32_params])
+        # quit()
         self.overflow = self.loss_scaler.update_scale()
 
 

csrc/scale_check_overflow.cpp → csrc/amp_C_frontend.cpp

 #include <torch/extension.h>
 
-void multi_tensor_unscale_cuda(
-  int nblocks,
-  at::Tensor noop_flag,
-  at::Tensor cpu_tensor_addresses,
-  at::Tensor gpu_block_to_tensor,
-  at::Tensor gpu_block_to_chunk,
-  at::Tensor gpu_tensor_sizes,
-  at::Tensor gpu_tensor_addresses,
+void multi_tensor_scale_cuda(
   int chunk_size,
+  at::Tensor noop_flag,
   std::vector<std::vector<at::Tensor>> tensor_lists,
   float scale);
 
-std::vector<int> prep_multi_tensor_launch(
-  at::Tensor cpu_block_to_tensor,
-  at::Tensor cpu_block_to_chunk,
-  at::Tensor cpu_tensor_sizes,
-  at::Tensor gpu_block_to_tensor,
-  at::Tensor gpu_block_to_chunk,
-  at::Tensor gpu_tensor_sizes,
-  int chunk_size,
-  int max_depth,
-  int max_tensors,
-  int max_blocks,
-  std::vector<std::vector<at::Tensor>> tensor_lists)
-{
-  int needs_reallocate = 0;
-
-  if(tensor_lists.size() > max_depth || tensor_lists[0].size() > max_tensors)
-    needs_reallocate = 1;
-
-  auto cpu_tensor_sizes_a = cpu_tensor_sizes.accessor<int,1>();
-  auto cpu_block_to_tensor_a = cpu_block_to_tensor.accessor<int,1>();
-  auto cpu_block_to_chunk_a = cpu_block_to_chunk.accessor<int,1>();
-
-  int nblocks = 0;
-  for(int t = 0; t < tensor_lists[0].size(); t++)
-  {
-    int blocks_this_tensor = (tensor_lists[0][t].numel() + chunk_size - 1)/chunk_size;
-    if(!needs_reallocate)
-      cpu_tensor_sizes_a[t] = tensor_lists[0][t].numel();
-    for(int chunk = 0; chunk < blocks_this_tensor; chunk++)
-    {
-      if(nblocks >= max_blocks)
-        needs_reallocate = 1;
-      if(!needs_reallocate)
-      {
-        cpu_block_to_tensor_a[nblocks] = t;
-        cpu_block_to_chunk_a[nblocks] = chunk;
-      }
-      nblocks++;
-    }
-  }
-
-  if(!needs_reallocate)
-  {
-    gpu_block_to_tensor.copy_(cpu_block_to_tensor, 1);
-    gpu_block_to_chunk.copy_(cpu_block_to_chunk, 1);
-    gpu_tensor_sizes.copy_(cpu_tensor_sizes, 1);
-  }
-
-  return std::vector<int>{needs_reallocate, nblocks};
-}
-
-void scale_check_overflow_cuda(const at::Tensor& grads,
+void scale_check_overflow_cuda(
+  const at::Tensor& grads,
   float scale,
   const at::Tensor& d_buf,
   const at::Tensor& downscaled_grads);
 
-void scale_check_overflow(at::Tensor grads,
+void scale_check_overflow(
+  at::Tensor grads,
   float scale,
   at::Tensor overflow_buf,
   at::Tensor downscaled_grads)
@@ -90,7 +35,6 @@ void scale_check_overflow(at::Tensor grads,
 
 PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
   m.def("scale_check_overflow", &scale_check_overflow, "Fused overflow check + scale for FP32 tensors");
-  m.def("prep_multi_tensor_launch", &prep_multi_tensor_launch, "Prepare multitensor launch");
-  m.def("multi_tensor_unscale", &multi_tensor_unscale_cuda,
-        "Fused overflow check + unscale for a list of contiguous tensors");
+  m.def("multi_tensor_scale", &multi_tensor_scale_cuda,
+        "Fused overflow check + scale for a list of contiguous tensors");
 }

csrc/multi_tensor_apply.cuh

+#include <torch/extension.h>
+#include <ATen/ATen.h>
+#include <ATen/AccumulateType.h>
+#include <ATen/cuda/CUDAContext.h>
+#include <ATen/cuda/Exceptions.h>
+
+#include <assert.h>
+#include <cuda_runtime.h>
+
+// #include <iostream>
+
+// This header is the one-stop shop for all your multi-tensor apply needs.
+
+constexpr int depth_to_max_tensors[5] = {110, 64, 48, 36, 30};
+constexpr int depth_to_max_blocks[5] = {320, 320, 320, 320, 320};
+
+template<int n> struct TensorList
+{
+  void* addresses[n][depth_to_max_tensors[n-1]];
+  int sizes[depth_to_max_tensors[n-1]];
+  int block_to_tensor[depth_to_max_blocks[n-1]];
+  int block_to_chunk[depth_to_max_blocks[n-1]]; 
+};
+
+
+template<typename T, typename U, typename... ArgTypes>
+__global__ void multi_tensor_apply_kernel(
+    int chunk_size,
+    volatile int* noop_flag,
+    T tl,
+    U callable,
+    ArgTypes... args) // in_t** in, float** out, float scale
+{
+  // Hand the chunk information to the user-supplied functor to process however it likes.
+  callable(chunk_size, noop_flag, tl, args...); 
+}
+
+template<int depth, typename T, typename... ArgTypes>
+void multi_tensor_apply(
+  int block_size,
+  int chunk_size,
+  const at::Tensor& noop_flag,
+  const std::vector<std::vector<at::Tensor>>& tensor_lists,
+  T callable,
+  ArgTypes... args)
+{
+  AT_CHECK(tensor_lists.size() > 0, "tensor_lists.size() is not > 0");
+  int len0 = tensor_lists[0].size();
+  AT_CHECK(len0 > 0, "tensor_lists[0].size() is not > 0");
+
+  for(int l = 0; l < tensor_lists.size(); l++) // No range-based for because I need indices
+  {
+    AT_CHECK(tensor_lists[l].size() == len0, "Size mismatch among tensor lists");
+    for(int t = 0; t < tensor_lists[l].size(); t++)
+    {
+      AT_CHECK(tensor_lists[l][t].is_contiguous(), "A tensor was not contiguous.");
+      AT_CHECK(tensor_lists[l][t].is_cuda(), "A tensor was not cuda.");
+      AT_CHECK(tensor_lists[l][t].numel() == tensor_lists[0][t].numel(), "Size mismatch");
+    }
+  }
+
+  int ntensors = tensor_lists[0].size();
+
+  TensorList<depth> tl;
+
+  auto stream = at::cuda::getCurrentCUDAStream();
+  
+  int loc_block_info = 0;
+  int loc_tensor_info = 0;
+  for(int t = 0; t < ntensors; t++)
+  {
+    tl.sizes[loc_tensor_info] = tensor_lists[0][t].numel();
+    for(int d = 0; d < depth; d++)
+      tl.addresses[d][loc_tensor_info] = tensor_lists[d][t].data_ptr();
+    loc_tensor_info++;
+
+    int chunks_this_tensor = (tensor_lists[0][t].numel() + chunk_size - 1)/chunk_size;
+
+    for(int chunk = 0; chunk < chunks_this_tensor; chunk++)
+    {
+      // std::cout << chunks_this_tensor << std::endl;
+      tl.block_to_tensor[loc_block_info] = loc_tensor_info - 1;
+      tl.block_to_chunk[loc_block_info] = chunk;
+      loc_block_info++;
+  
+      bool tensors_full = (loc_tensor_info == depth_to_max_tensors[depth-1] &&
+                           chunk == chunks_this_tensor - 1);
+      bool blocks_full = (loc_block_info == depth_to_max_blocks[depth-1]);
+      bool last_chunk = (t == ntensors - 1 && chunk == chunks_this_tensor - 1);
+      if(tensors_full || blocks_full || last_chunk)
+      {
+        // using accscalar_t = acc_type<scalar_t, true>;
+        multi_tensor_apply_kernel<<<loc_block_info, block_size, 0, stream>>>(
+          chunk_size,
+          noop_flag.data<int>(),
+          tl,
+          callable,
+          args...);
+
+        AT_CUDA_CHECK(cudaGetLastError());
+
+        // Reset.  The control flow possibilities here make my brain hurt.
+        loc_block_info = 0;
+        if(chunk == chunks_this_tensor - 1)
+        {
+          // std::cout << "Hit case 1 " << cond1 << " " << cond2 << " " << cond3 << std::endl;
+          loc_tensor_info = 0; 
+        }
+        else
+        {
+          // std::cout << "Hit case 2 " << cond1 << " " << cond2 << " " << cond3 << std::endl;
+          for(int d = 0; d < depth; d++)
+            tl.addresses[d][0] = tl.addresses[d][loc_tensor_info-1];
+          tl.sizes[0] = tl.sizes[loc_tensor_info-1];
+          loc_tensor_info = 1;
+        }
+      }
+    }
+  }
+}

csrc/multi_tensor_apply.h

-#include <ATen/ATen.h>
-#include <ATen/AccumulateType.h>
-#include <ATen/cuda/CUDAContext.h>
-#include <ATen/cuda/Exceptions.h>
-
-#include <assert.h>
-#include <cuda_runtime.h>
-
-template<typename T, typename... ArgTypes>
-__global__ void multi_tensor_apply_kernel(
-    volatile int* noop_flag,
-    int* block_to_tensor,
-    int* block_to_chunk, // could also get this from scan
-    int* tensor_sizes,
-    int chunk_size,
-    void** addresses,
-    int addresses_x,
-    T callable,
-    ArgTypes... args) // in_t** in, float** out, float scale
-{
-  __shared__ int noop;
-  __shared__ int chunk_idx;
-  __shared__ int tensor_idx;
-  __shared__ int n;
-
-  if(threadIdx.x == 0)
-  {
-    noop = *noop_flag;
-    tensor_idx = block_to_tensor[blockIdx.x]; 
-    chunk_idx = block_to_chunk[blockIdx.x];
-    n = tensor_sizes[tensor_idx]; 
-  }
-
-  __syncthreads();
-
-  if(noop == 1)
-    return;
-
-  // Hand the chunk information to the user-supplied functor to process however it likes.
-  callable(
-    noop_flag,
-    tensor_idx,
-    chunk_idx,
-    chunk_size,
-    n,
-    addresses,
-    addresses_x,
-    args...);
-}

csrc/multi_tensor_unscale_kernel.cu → csrc/multi_tensor_scale_kernel.cu

@@ -2,33 +2,39 @@
 #include <ATen/AccumulateType.h>
 #include <ATen/cuda/CUDAContext.h>
 #include <ATen/cuda/Exceptions.h>
-#include "multi_tensor_apply.h"
+#include "multi_tensor_apply.cuh"
 
 #include <assert.h>
 #include <cuda_runtime.h>
 
-#define BLOCK_SIZE 256
+#define BLOCK_SIZE 512
 #define ILP 4
 
 template<typename in_t>
-struct UnscaleFunctor
+struct ScaleFunctor
 {
    __device__ __forceinline__ void operator()(
-    volatile int* noop_flag,
-    int tensor_idx,
-    int chunk_idx,
     int chunk_size,
-    int n,
-    void** addresses,
-    int addresses_x,
+    volatile int* noop_gmem,
+    TensorList<2>& tl,
     float scale)
   {
-    __shared__ int noop;
+    __shared__ int noop_smem;
 
-    in_t* in = (in_t*)addresses[tensor_idx];
+    if(threadIdx.x == 0)
+      noop_smem = *noop_gmem;
+    __syncthreads();
+    if(noop_smem == 1)
+      return;
+
+    int tensor_loc = tl.block_to_tensor[blockIdx.x];
+    int chunk_idx = tl.block_to_chunk[blockIdx.x];
+    int n = tl.sizes[tensor_loc];
+
+    in_t* in = (in_t*)tl.addresses[0][tensor_loc];
     in += chunk_idx*chunk_size;
    
-    float* out = (float*)addresses[addresses_x + tensor_idx];
+    float* out = (float*)tl.addresses[1][tensor_loc];
     out += chunk_idx*chunk_size;
 
     n -= chunk_idx*chunk_size;
@@ -39,14 +45,6 @@ struct UnscaleFunctor
         i_start < n && i_start < chunk_size;
         i_start += blockDim.x*ILP)
     {
-      if(threadIdx.x == 0)
-        noop = *noop_flag;
-
-      __syncthreads();
-
-      if(noop == 1)
-        break;
-
       #pragma unroll
       for(int ii = 0; ii < ILP; ii++)
       {
@@ -56,6 +54,11 @@ struct UnscaleFunctor
           incoming_vals[ii] = static_cast<float>(in[i]);
       }
 
+      // note for clarification to future michael:
+      // From a pure memory dependency perspective, there's likely no point unrolling
+      // the write loop, since writes just fire off once their LDGs arrive.
+      // Put another way, the STGs are dependent on the LDGs, but not on each other.
+      // There is still compute ILP benefit from unrolling the loop though.
       #pragma unroll
       for(int ii = 0; ii < ILP; ii++)
       {
@@ -64,73 +67,45 @@ struct UnscaleFunctor
           if(isfinite(incoming_vals[ii]))
             out[i] = incoming_vals[ii]*scale;
           else
-            *noop_flag = 1; // Blindly fire off a write.  These will race but that's ok.
-      }    // This is NOT guaranteed to be seen immediately by thread 0 on the next iteration.
-    }      // I wonder if there's a way we can rig the short-circuiting with only one syncthreads.
-  }        // It's possible we can just lean on the cache (no smem or syncs) and still be fast.
-};
+            *noop_gmem = 1; // Blindly fire off a write.  These will race but that's ok.
+      }
 
+      // *noop_gmem = 1 is NOT guaranteed to be seen immediately by thread 0.  I wonder if
+      // we can rig block-wide and grid-wide short-circuiting with only one syncthreads.
+      // It's possible we can just lean on the cache (no smem or syncs) and still be fast.
+      if(threadIdx.x == 0)
+        noop_smem = *noop_gmem;
+      __syncthreads();
+      if(noop_smem == 1)
+        break;
+    }
+  }
+};
 
-void multi_tensor_unscale_cuda(
-  int nblocks,
-  at::Tensor noop_flag,
-  at::Tensor cpu_tensor_addresses,
-  at::Tensor gpu_block_to_tensor,
-  at::Tensor gpu_block_to_chunk,
-  at::Tensor gpu_tensor_sizes,
-  at::Tensor gpu_tensor_addresses,
+void multi_tensor_scale_cuda(
   int chunk_size,
+  at::Tensor noop_flag,
   std::vector<std::vector<at::Tensor>> tensor_lists,
   float scale)
 {
-  using namespace at;
-
-  AT_CHECK(nblocks > 0, "nblocks is not > 0");
-
-  int addresses_x = gpu_tensor_addresses.size(1);
-
-  // <.< >.> i don't see any cops. i'm going to access the pointers directly.
-  // auto addresses_a = cpu_tensor_addresses.accessor<int64_t, 2>();
-  // This logic could be moved to prep_multi_tensor_launch, but we might need to
-  // pick which kernel instantiation to launch based on the RTTI of tensor_lists,
-  // so we may as well accept tensor_lists and extract the pointers here.
-  void** addresses_a = (void**)cpu_tensor_addresses.data_ptr();
-
-  int len0 = tensor_lists[0].size();
-  for(unsigned int l = 0; l < tensor_lists.size(); l++)
-  {
-    AT_CHECK(tensor_lists[l].size() == len0, "Lengths of tensor lists do not match.");
-    for(unsigned int t = 0; t < tensor_lists[l].size(); t++)
-    {
-      AT_CHECK(tensor_lists[l][t].numel() == tensor_lists[0][t].numel(),
-        "Numel mismatch in corresponding tensors in different lists.");
-      addresses_a[l*addresses_x + t] = tensor_lists[l][t].data_ptr();
-      // addresses_a[l][t] = (void*)tensor_lists[l][t].data<float>();
-    }
-  }
-
-  cudaStream_t stream = at::cuda::getCurrentCUDAStream();
-
-  gpu_tensor_addresses.copy_(cpu_tensor_addresses, 1/*non_blocking*/);
- 
-  // Lock the output (downscaled) type to float.
+  // The output (downscaled) type is always float.
+  // If build times suffer, think about where to put this dispatch,
+  // and what logic should be moved out of multi_tensor_apply.
   AT_DISPATCH_FLOATING_TYPES_AND_HALF(tensor_lists[0][0].type(),
-     "multi_tensor_unscale_cuda",
+     "multi_tensor_scale_cuda",
      [&]
      {
        // using accscalar_t = acc_type<scalar_t, true>;
-       multi_tensor_apply_kernel<<<nblocks, BLOCK_SIZE, 0, stream>>>(
-         noop_flag.data<int>(),
-         gpu_block_to_tensor.data<int>(),
-         gpu_block_to_chunk.data<int>(),
-         gpu_tensor_sizes.data<int>(),
+       multi_tensor_apply<2>(
+         BLOCK_SIZE,
          chunk_size,
-         (void**)gpu_tensor_addresses.data_ptr(),
-         addresses_x,
-         UnscaleFunctor<scalar_t>(),
+         noop_flag,
+         tensor_lists,
+         ScaleFunctor<scalar_t>(),
          scale);
      });
 
   AT_CUDA_CHECK(cudaGetLastError());
+
   // AT_CUDA_CHECK(cudaDeviceSynchronize());
 }

examples/imagenet/main_fp16_optimizer.py

@@ -139,7 +139,7 @@ def main():
 
     model = model.cuda()
     if args.fp16:
-        model = network_to_half(model)
+        model = FP16Model(model)
     if args.distributed:
         # By default, apex.parallel.DistributedDataParallel overlaps communication with 
         # computation in the backward pass.

setup.py

@@ -38,10 +38,10 @@ if "--cuda_ext" in sys.argv:
     else:
         ext_modules.append(
             CUDAExtension(name='amp_C',
-                          sources=['csrc/scale_check_overflow.cpp',
+                          sources=['csrc/amp_C_frontend.cpp',
                                    'csrc/scale_check_overflow_kernel.cu',
-                                   'csrc/multi_tensor_unscale_kernel.cu'],
-                          extra_compile_args={'cxx': ['-O3',],
+                                   'csrc/multi_tensor_scale_kernel.cu'],
+                          extra_compile_args={'cxx': ['-O3'],
                                               'nvcc':['-lineinfo',
                                                       '-O3',
                                                       '--use_fast_math']}))

tests/run_amp/test_multi_tensor_scale.py

+import unittest
+
+import functools as ft
+import itertools as it
+
+from apex import amp
+import torch
+from torch import nn
+import torch.nn.functional as F
+
+from utils import common_init, HALF, FLOAT,\
+    ALWAYS_HALF, ALWAYS_FLOAT, MATCH_INPUT
+
+try:
+  import amp_C
+  from amp_C import multi_tensor_scale 
+  from apex.multi_tensor_apply import MultiTensorApply
+  disabled = False
+except ImportError as err:
+  print("amp_C fused kernels unavailable, disabling TestMultiTensorApply.  ImportError was ", err)
+  disabled = True
+
+
+class TestMultiTensorScale(unittest.TestCase):
+
+    def setUp(self):
+        self.scale = 4.0
+        self.overflow_buf = torch.cuda.IntTensor(1).zero_()
+        self.ref = torch.cuda.FloatTensor([1.0])
+
+        common_init(self)
+
+    def tearDown(self):
+        pass
+
+    # The tensor creation here is written for convenience, not speed.
+    def downscale(self, sizea, sizeb, applier, repeat_tensors, in_type, inplace=False):
+        self.overflow_buf.zero_()
+        a = torch.cuda.FloatTensor(sizea).fill_(self.scale)
+        b = torch.cuda.FloatTensor(sizeb).fill_(self.scale)
+
+        out_list = []
+        for i in range(repeat_tensors):
+            out_list += [a.clone(), b.clone()]
+
+        if inplace:
+            in_list = out_list
+        else:
+            in_list = [out.clone().to(in_type) for out in out_list]
+
+        applier(multi_tensor_scale, self.overflow_buf, [in_list, out_list], 1./self.scale)
+
+        self.assertTrue(all([torch.allclose(out, self.ref) for out in out_list]))
+        self.assertTrue(self.overflow_buf.item() == 0)
+ 
+    def find_inf(self, sizea, sizeb, applier, repeat_tensors, in_type, t, ind, val, inplace=False):
+        self.overflow_buf.zero_()
+        a = torch.cuda.FloatTensor(sizea).fill_(self.scale)
+        b = torch.cuda.FloatTensor(sizeb).fill_(self.scale)
+
+        out_list = []
+        for i in range(repeat_tensors):
+            out_list += [a.clone(), b.clone()]
+
+        if inplace:
+            in_list = out_list
+        else:
+            in_list = [out.clone().to(in_type) for out in out_list]
+
+        applier(multi_tensor_scale, self.overflow_buf, [in_list, out_list], 1./self.scale)
+
+        self.overflow_buf.zero_()
+        in_list[t][ind] = val
+        applier(multi_tensor_scale, self.overflow_buf, [in_list, out_list], 1./self.scale)
+        self.assertTrue(self.overflow_buf.item())
+
+    # Currently, the fused kernel gives a hard error if you attempt to downscale
+    # into fp16 output, which imo is the desired behavior.  Maybe someday we
+    # will learn otherwise.
+    # @unittest.skipIf(disabled, "amp_C is unavailable")
+    # def test_fp16_to_fp16(self):
+    #     self.downscale(self.fp16, self.fp16, self.fp16_ref)
+    # 
+    # @unittest.skipIf(disabled, "amp_C is unavailable")
+    # def test_fp32_to_fp16(self):
+    #     self.downscale(self.fp32, self.fp16, self.fp16_ref)
+
+    @unittest.skipIf(disabled, "amp_C is unavailable")
+    def test_fuzz(self):
+        input_size_pairs = (
+            (7777*77, 555*555),
+            (777, 555),
+            (555, 2048*32+1),
+            (2048*32+1, 555),
+            (555, 2048*32),
+            (2048*32, 555),
+            (33333, 555),
+            (555, 33333))
+        appliers = (
+            MultiTensorApply(2048*32), 
+            MultiTensorApply(333),
+            MultiTensorApply(33333))
+        repeat_tensors = (
+            1,
+            55)
+        dtype_inplace_pairs = (
+            (torch.float16, False),
+            (torch.float32, False),
+            (torch.float32, True))
+
+        for sizea, sizeb in input_size_pairs:
+          for applier in appliers:
+            for repeat in repeat_tensors:
+              for dtype, inplace in dtype_inplace_pairs:
+                self.downscale(sizea, sizeb, applier, repeat, dtype, inplace=inplace)
+                self.find_inf(sizea, sizeb, applier, repeat, dtype,
+                              0, 0, float('nan'), inplace=inplace)
+                self.find_inf(sizea, sizeb, applier, repeat, dtype,
+                              2*repeat-1, sizeb-1, float('inf'), inplace=inplace)
+                self.find_inf(sizea, sizeb, applier, repeat, dtype,
+                             2*(repeat//2), sizea//2, float('inf'), inplace=inplace)
+
+
+
+if __name__ == '__main__':
+    unittest.main()