Merge branch 'multi_tensor_sgd' into deyuf/fused_optimizer_v2

README.md

 # Introduction
 
-This repository holds NVIDIA-maintained utilities to streamline 
-mixed precision and distributed training in Pytorch. 
+This repository holds NVIDIA-maintained utilities to streamline
+mixed precision and distributed training in Pytorch.
 Some of the code here will be included in upstream Pytorch eventually.
-The intention of Apex is to make up-to-date utilities available to 
+The intention of Apex is to make up-to-date utilities available to
 users as quickly as possible.
 
 ## Full API Documentation: [https://nvidia.github.io/apex](https://nvidia.github.io/apex)
@@ -29,7 +29,7 @@ different flags to `amp.initialize`.
 
 ## 2. Distributed Training
 
-`apex.parallel.DistributedDataParallel` is a module wrapper, similar to 
+`apex.parallel.DistributedDataParallel` is a module wrapper, similar to
 `torch.nn.parallel.DistributedDataParallel`.  It enables convenient multiprocess distributed training,
 optimized for NVIDIA's NCCL communication library.
 

apex/amp/_initialize.py

@@ -124,29 +124,13 @@ def check_optimizers(optimizers):
             raise RuntimeError("An incoming optimizer is an instance of {}. ".format(bad_optim_type) +
                                "The optimizer(s) passed to amp.initialize() must be bare \n"
                                "instances of either ordinary Pytorch optimizers, or Apex fused \n"
-                               "optimizers (currently just FusedAdam, but FusedSGD will be added \n"
-                               "soon).  You should not manually wrap your optimizer in either \n"
+                               "optimizers (FusedAdam or FusedSGD). \n"
+                               "You should not manually wrap your optimizer in either \n"
                                "apex.fp16_utils.FP16_Optimizer or apex.optimizers.FP16_Optimizer. \n"
                                "amp.initialize will take care of that for you (if necessary) based \n"
                                "on the specified opt_level (and optional overridden properties).")
 
 
-def wrap_fused_adam(optimizer, properties):
-    msg = 'Currently, the usage of FusedAdam is restricted to '\
-          'amp.initialize(..., opt_level="O2", keep_batchnorm_fp32=False, '\
-          'loss_scale=float or "dynamic").  We are working on enabling more general usage.'
-
-    assert properties.master_weights is True, msg
-    assert properties.cast_model_type is torch.float16, msg
-    assert (properties.keep_batchnorm_fp32 is False or
-            properties.keep_batchnorm_fp32 is None), msg
-
-    if properties.loss_scale == "dynamic":
-        return FP16_Optimizer_for_fused(optimizer, dynamic_loss_scale=True)
-    else:
-        return FP16_Optimizer_for_fused(optimizer, static_loss_scale=properties.loss_scale)
-
-
 def _initialize(models, optimizers, properties, num_losses=1, cast_model_outputs=None):
     from apex.parallel import DistributedDataParallel as apex_DDP
     from .amp import init as amp_init
@@ -176,7 +160,6 @@ def _initialize(models, optimizers, properties, num_losses=1, cast_model_outputs
     if not _amp_state.allow_incoming_model_not_fp32:
         check_params_fp32(models)
 
-
     # In the future, when FP16_Optimizer can be deprecated and master weights can
     # become an attribute, remember to stash master weights before casting the model.
 
@@ -207,7 +190,7 @@ def _initialize(models, optimizers, properties, num_losses=1, cast_model_outputs
 
             model.forward = patch_forward(model.forward)
 
-        # State dict trick to recast any preexisting per-param state tensors 
+        # State dict trick to recast any preexisting per-param state tensors
         for optimizer in optimizers:
             optimizer.load_state_dict(optimizer.state_dict())
     elif cast_model_outputs is not None:
@@ -223,11 +206,7 @@ def _initialize(models, optimizers, properties, num_losses=1, cast_model_outputs
             model.forward = patch_forward(model.forward)
 
     for i, optimizer in enumerate(optimizers):
-        # Still need to special case this for the first pass
-        if isinstance(optimizer, FusedAdam):
-            optimizers[i] = wrap_fused_adam(optimizer, properties)
-        else:
-            optimizers[i] = _process_optimizer(optimizer, properties)
+        optimizers[i] = _process_optimizer(optimizer, properties)
 
     _amp_state.loss_scalers = []
     for _ in range(num_losses):

apex/amp/_process_optimizer.py

@@ -3,6 +3,7 @@ from ..fp16_utils import master_params_to_model_params
 from ..multi_tensor_apply import multi_tensor_applier
 from ._amp_state import maybe_print
 import torch
+from ..optimizers import FusedAdam, FusedSGD
 
 
 class AmpOptimizerState(object):
@@ -10,6 +11,20 @@ class AmpOptimizerState(object):
         pass
 
 
+def _master_params_to_model_params(self):
+    stash = self._amp_stash
+    if multi_tensor_applier.available:
+        if len(stash.all_fp16_params) > 0:
+            multi_tensor_applier(
+                stash.multi_tensor_scale,
+                stash.dummy_overflow_buf,
+                [stash.all_fp32_from_fp16_params, stash.all_fp16_params],
+                1.0)
+    else:
+        for fp16_group, fp32_from_fp16_group in zip(stash.fp16_groups, stash.fp32_from_fp16_groups):
+            master_params_to_model_params(fp16_group, fp32_from_fp16_group)
+
+
 def lazy_init_with_master_weights(self):
         stash = self._amp_stash
         stash.fp16_groups = []
@@ -60,6 +75,8 @@ def lazy_init_with_master_weights(self):
         for group in stash.fp32_from_fp32_groups:
             stash.all_fp32_from_fp32_params += group
 
+        # all_fp16_grad_stash is only needed for fused optimizers.
+        stash.all_fp16_grad_stash = [None for _ in stash.all_fp16_params]
         # stash.all_fp32_from_fp16_grad_stash = [None for _ in stash.all_fp32_from_fp16_params]
         stash.all_fp32_from_fp32_grad_stash = [None for _ in stash.all_fp32_from_fp32_params]
 
@@ -73,15 +90,55 @@ def lazy_init_with_master_weights(self):
         self.load_state_dict(self.state_dict())
 
 
+def post_backward_models_are_masters(scaler, params, stashed_grads, scale_override=None):
+        grads_have_scale, stashed_have_scale, out_scale = scaler.loss_scale(), 1.0, 1.0
+        if scale_override is not None:
+            grads_have_scale, stashed_have_scale, out_scale = scale_override
+
+        # This is a lot of python overhead...
+        grads_needing_unscale = []
+        grads_needing_unscale_with_stash = []
+        stashed = []
+        for param, stashed_grad in zip(params, stashed_grads):
+            if param.grad is None and stashed_grad is not None:
+                param.grad = stashed_grad
+            elif param.grad is not None and stashed_grad is None:
+                grads_needing_unscale.append(param.grad)
+            elif param.grad is not None and stashed_grad is not None:
+                grads_needing_unscale_with_stash.append(param.grad)
+                stashed.append(stashed_grad)
+            else: # param.grad is None and stashed_grad is None
+                continue
+
+        # unscale() implements grads*(1/scale), so "scale" should be grads_have_scale/out_scale.
+        if len(grads_needing_unscale) > 0:
+            scaler.unscale(
+                grads_needing_unscale,
+                grads_needing_unscale,
+                None, # unused_scale, currently present to avoid API breakage elsewhere
+                models_are_masters=True,
+                scale_override=grads_have_scale/out_scale)
+
+        if len(grads_needing_unscale_with_stash) > 0:
+            scaler.unscale_with_stashed(
+                grads_needing_unscale_with_stash,
+                stashed,
+                grads_needing_unscale_with_stash,
+                scale_override=(grads_have_scale, stashed_have_scale, out_scale))
+
+        # Clear the stash.
+        for i in range(len(stashed_grads)):
+            stashed_grads[i] = None
+
+
 def prepare_backward_with_master_weights(self):
     stash = self._amp_stash
 
-    if not stash.lazy_init_called:
-        self._lazy_init_maybe_master_weights()
-        stash.lazy_init_called = True
+    self._amp_lazy_init()
 
     for i, param in enumerate(stash.all_fp16_params):
-        # Set up to leverage grad copy elision:
+        # Set up to leverage grad copy elision.
+        # This may behave differently from an unpatched optimizer if zero_grad is used and the param is unused.
         param.grad = None
 
     # for i, param in enumerate(stash.all_fp32_from_fp16_params):
@@ -96,6 +153,8 @@ def prepare_backward_with_master_weights(self):
 def post_backward_with_master_weights(self, scaler):
     stash = self._amp_stash
 
+    self._amp_lazy_init()
+
     # This is a lot of python overhead...
     fp16_grads_needing_unscale = []
     new_fp32_grads = []
@@ -129,37 +188,10 @@ def post_backward_with_master_weights(self, scaler):
             preexisting_fp32_grads)
 
     # fp32 params can be treated as they would be in the "no_master_weights" case.
-    grads_needing_unscale = []
-    grads_needing_unscale_with_stash = []
-    stashed = []
-    for param, stashed_grad in zip(stash.all_fp32_from_fp32_params,
-                                   stash.all_fp32_from_fp32_grad_stash):
-        if param.grad is None and stashed_grad is not None:
-            param.grad = stashed_grad
-        elif param.grad is not None and stashed_grad is None:
-            grads_needing_unscale.append(param.grad)
-        elif param.grad is not None and stashed_grad is not None:
-            grads_needing_unscale_with_stash.append(param.grad)
-            stashed.append(stashed_grad)
-        else: # param.grad is None and stashed_grad is None:
-            continue
-
-    if len(grads_needing_unscale) > 0:
-        scaler.unscale(
-            grads_needing_unscale,
-            grads_needing_unscale,
-            scaler.loss_scale(),
-            models_are_masters=True)
-
-    if len(grads_needing_unscale_with_stash) > 0:
-        scaler.unscale_with_stashed(
-            grads_needing_unscale_with_stash,
-            stashed,
-            grads_needing_unscale_with_stash)
-
-    # Clear the stash.
-    for i in range(len(stash.all_fp32_from_fp32_grad_stash)):
-        stash.all_fp32_from_fp32_grad_stash[i] = None
+    post_backward_models_are_masters(
+        scaler,
+        stash.all_fp32_from_fp32_params,
+        stash.all_fp32_from_fp32_grad_stash)
 
 
 def lazy_init_no_master_weights(self):
@@ -184,9 +216,7 @@ def lazy_init_no_master_weights(self):
 def prepare_backward_no_master_weights(self):
     stash = self._amp_stash
 
-    if not stash.lazy_init_called:
-        self._lazy_init_maybe_master_weights()
-        stash.lazy_init_called = True
+    self._amp_lazy_init()
 
     for i, param in enumerate(stash.all_fp16_params):
         stash.all_fp16_grad_stash[i] = param.grad
@@ -202,55 +232,141 @@ def prepare_backward_no_master_weights(self):
 def post_backward_no_master_weights(self, scaler):
     stash = self._amp_stash
 
+    self._amp_lazy_init()
+
     split_types = ((stash.all_fp16_params, stash.all_fp16_grad_stash),
              (stash.all_fp32_params, stash.all_fp32_grad_stash))
 
     for params, stashed_grads in split_types:
-        # This is a lot of python overhead...
-        grads_needing_unscale = []
-        grads_needing_unscale_with_stash = []
-        stashed = []
-        for param, stashed_grad in zip(params, stashed_grads):
-            if param.grad is None and stashed_grad is not None:
-                param.grad = stashed_grad
-            elif param.grad is not None and stashed_grad is None:
-                grads_needing_unscale.append(param.grad)
-            elif param.grad is not None and stashed_grad is not None:
-                grads_needing_unscale_with_stash.append(param.grad)
-                stashed.append(stashed_grad)
-            else: # param.grad is None and stashed_grad is None
-                continue
+        post_backward_models_are_masters(scaler, params, stashed_grads)
 
-        if len(grads_needing_unscale) > 0:
-            scaler.unscale(
-                grads_needing_unscale,
-                grads_needing_unscale,
-                scaler.loss_scale(),
-                models_are_masters=True)
 
-        if len(grads_needing_unscale_with_stash) > 0:
-            scaler.unscale_with_stashed(
-                grads_needing_unscale_with_stash,
-                stashed,
-                grads_needing_unscale_with_stash)
+#####################################################################################
+# FusedAdam versions
+#####################################################################################
 
-        # Clear the stash.
-        for i in range(len(stashed_grads)):
-            stashed_grads[i] = None
+def prepare_backward_with_master_weights_FusedAdam(self):
+    stash = self._amp_stash
 
+    self._amp_lazy_init()
 
-def _master_params_to_model_params(self):
+
+def post_backward_with_master_weights_FusedAdam(self, scaler):
     stash = self._amp_stash
-    if multi_tensor_applier.available:
-        if len(stash.all_fp16_params) > 0:
-            multi_tensor_applier(
-                stash.multi_tensor_scale,
-                stash.dummy_overflow_buf,
-                [stash.all_fp32_from_fp16_params, stash.all_fp16_params],
-                1.0)
+
+    self._amp_lazy_init()
+
+    stash.scale = scaler.loss_scale()
+    stash.grads = [[param.grad.data for param in group] for group in stash.fp16_groups]
+    stash.output_params = [[param for param in group] for group in stash.fp16_groups]
+
+    norm_groups = []
+    skip = False
+    for grad_group in stash.grads:
+        norm, _ = multi_tensor_applier(
+            stash.multi_tensor_l2norm,
+            stash.dummy_overflow_buf,
+            [grad_group],
+            False)
+        # Still syncing here for now.
+        norm = float(norm)
+        norm_groups.append(norm)
+        if norm == float('inf') or norm == -float('inf') or norm != norm:
+            skip = True
+    if skip:
+        scaler._overflow_buf.fill_(1.)
+        scaler._has_overflow = True
+
+    stash.grad_norms = norm_groups
+
+
+def prepare_backward_no_master_weights_FusedAdam(self):
+    stash = self._amp_stash
+
+    self._amp_lazy_init()
+
+
+def post_backward_no_master_weights_FusedAdam(self, scaler):
+    stash = self._amp_stash
+
+    self._amp_lazy_init()
+
+    stash.scale = scaler.loss_scale()
+    stash.grads = None
+    stash.output_params = None
+    stash.grad_norms = None
+
+
+#####################################################################################
+# FusedSGD versions
+# Eat this ugly code duplication for now.  First make it work, then make it clean.
+# It's difficult to anticipate what can be unified between the FusedAdam and FusedSGD
+# implementations until I have them both working.
+#####################################################################################
+
+# FusedSGD never explicitly materializes the fp32 gradients for "fp32 from fp16" master params
+# outside the kernel, so we must accumulate directly into the model grads.
+def prepare_backward_with_master_weights_FusedSGD(self):
+    if self.materialize_master_grads:
+        prepare_backward_with_master_weights(self)
     else:
-        for fp16_group, fp32_from_fp16_group in zip(stash.fp16_groups, stash.fp32_from_fp16_groups):
-            master_params_to_model_params(fp16_group, fp32_from_fp16_group)
+        stash = self._amp_stash
+
+        self._amp_lazy_init()
+
+        for i, param in enumerate(stash.all_fp16_params):
+            stash.all_fp16_grad_stash[i] = param.grad
+            # Set up to leverage grad copy elision:
+            param.grad = None
+
+        for i, param in enumerate(stash.all_fp32_from_fp32_params):
+            stash.all_fp32_from_fp32_grad_stash[i] = param.grad
+            # Set up to leverage grad copy elision:
+            param.grad = None
+
+
+def post_backward_with_master_weights_FusedSGD(self, scaler):
+    if self.materialize_master_grads:
+        post_backward_with_master_weights(self, scaler)
+    else:
+        stash = self._amp_stash
+
+        self._amp_lazy_init()
+
+        grads_have_scale = scaler.loss_scale()
+        stashed_have_scale = self.most_recent_scale
+        out_scale = grads_have_scale
+        if self.scale_set_by_backward:
+            out_scale = min(grads_have_scale, self.most_recent_scale)
+
+        split_types = ((stash.all_fp16_params, stash.all_fp16_grad_stash),
+                 (stash.all_fp32_from_fp32_params, stash.all_fp32_from_fp32_grad_stash))
+
+
+        # unscale_with_stashed() implements grads*1/scale + stashed_grads*1.
+        # stashed_grads are scaled by self.most_recent_scale.
+        for params, stashed_grads in split_types:
+            post_backward_models_are_masters(scaler, params, stashed_grads,
+                                             (grads_have_scale, stashed_have_scale, out_scale))
+
+        self.most_recent_scale = out_scale
+        self.scale_set_by_backward = True
+
+
+def prepare_backward_no_master_weights_FusedSGD(self):
+    prepare_backward_no_master_weights(self)
+
+
+def post_backward_no_master_weights_FusedSGD(self, scaler):
+    post_backward_no_master_weights(self, scaler)
+
+
+def _amp_lazy_init(self):
+    stash = self._amp_stash
+
+    if not stash.lazy_init_called:
+        self._lazy_init_maybe_master_weights()
+        stash.lazy_init_called = True
 
 
 def _process_optimizer(optimizer, properties):
@@ -266,7 +382,8 @@ def _process_optimizer(optimizer, properties):
     for name in ("_lazy_init_maybe_master_weights",
                  "_master_params_to_model_params",
                  "_prepare_amp_backward",
-                 "_post_amp_backward"):
+                 "_post_amp_backward",
+                 "_amp_lazy_init"):
         if hasattr(optimizer, name):
             raise RuntimeError("Incoming optimizer already has {} defined.".format(name))
 
@@ -274,6 +391,7 @@ def _process_optimizer(optimizer, properties):
     if multi_tensor_applier.available:
         import amp_C
         optimizer._amp_stash.multi_tensor_scale = amp_C.multi_tensor_scale
+        optimizer._amp_stash.multi_tensor_l2norm = amp_C.multi_tensor_l2norm
         optimizer._amp_stash.dummy_overflow_buf = torch.cuda.IntTensor([0]);
 
     if properties.master_weights:
@@ -288,7 +406,8 @@ def _process_optimizer(optimizer, properties):
             if closure is not None:
                 raise RuntimeError("Currently, Amp does not support closure use with optimizers.")
             retval = old_step()
-            self._master_params_to_model_params()
+            if not (isinstance(self, FusedAdam) or isinstance(self, FusedSGD)):
+                self._master_params_to_model_params()
             # Clear the master grads that wouldn't be zeroed by model.zero_grad()
             for param in self._amp_stash.all_fp32_from_fp16_params:
                 param.grad = None
@@ -298,9 +417,7 @@ def _process_optimizer(optimizer, properties):
         old_zero_grad = optimizer.zero_grad
         def new_zero_grad(self):
             stash = self._amp_stash
-            if not stash.lazy_init_called:
-                self._lazy_init_maybe_master_weights()
-                stash.lazy_init_called = True
+            self._amp_lazy_init()
             # Zero the model grads.
             for param in stash.all_fp16_params:
                 if param.grad is not None:
@@ -315,20 +432,42 @@ def _process_optimizer(optimizer, properties):
                 param.grad = None
         optimizer.zero_grad = types.MethodType(new_zero_grad, optimizer)
 
-        optimizer._prepare_amp_backward = types.MethodType(
-            prepare_backward_with_master_weights, optimizer)
-
-        optimizer._post_amp_backward = types.MethodType(
-            post_backward_with_master_weights, optimizer)
+        if isinstance(optimizer, FusedAdam):
+            optimizer._prepare_amp_backward = types.MethodType(
+                prepare_backward_with_master_weights_FusedAdam, optimizer)
+            optimizer._post_amp_backward = types.MethodType(
+                post_backward_with_master_weights_FusedAdam, optimizer)
+        elif isinstance(optimizer, FusedSGD):
+            optimizer._prepare_amp_backward = types.MethodType(
+                prepare_backward_with_master_weights_FusedSGD, optimizer)
+            optimizer._post_amp_backward = types.MethodType(
+                post_backward_with_master_weights_FusedSGD, optimizer)
+        else:
+            optimizer._prepare_amp_backward = types.MethodType(
+                prepare_backward_with_master_weights, optimizer)
+            optimizer._post_amp_backward = types.MethodType(
+                post_backward_with_master_weights, optimizer)
     else:
         optimizer._lazy_init_maybe_master_weights = types.MethodType(
             lazy_init_no_master_weights, optimizer)
 
-        optimizer._prepare_amp_backward = types.MethodType(
-            prepare_backward_no_master_weights, optimizer)
+        if isinstance(optimizer, FusedAdam):
+            optimizer._prepare_amp_backward = types.MethodType(
+                prepare_backward_no_master_weights_FusedAdam, optimizer)
+            optimizer._post_amp_backward = types.MethodType(
+                post_backward_no_master_weights_FusedAdam, optimizer)
+        elif isinstance(optimizer, FusedSGD):
+            optimizer._prepare_amp_backward = types.MethodType(
+                prepare_backward_no_master_weights_FusedSGD, optimizer)
+            optimizer._post_amp_backward = types.MethodType(
+                post_backward_no_master_weights_FusedSGD, optimizer)
+        else:
+            optimizer._prepare_amp_backward = types.MethodType(
+                prepare_backward_no_master_weights, optimizer)
+            optimizer._post_amp_backward = types.MethodType(
+                post_backward_no_master_weights, optimizer)
 
-        optimizer._post_amp_backward = types.MethodType(
-            post_backward_no_master_weights, optimizer)
+    optimizer._amp_lazy_init = types.MethodType(_amp_lazy_init, optimizer)
 
     old_add_param_group = optimizer.add_param_group
 

apex/amp/handle.py

@@ -6,8 +6,6 @@ from . import utils
 from .opt import OptimWrapper
 from .scaler import LossScaler
 from ._amp_state import _amp_state, master_params, maybe_print
-from ..fp16_utils import FP16_Optimizer as FP16_Optimizer_general
-from ..optimizers import FP16_Optimizer as FP16_Optimizer_for_fused
 from ..parallel.LARC import LARC
 
 
@@ -89,13 +87,8 @@ def scale_loss(loss,
     if isinstance(optimizers, torch.optim.Optimizer) or isinstance(optimizers, LARC):
         optimizers = [optimizers]
 
-    # this is what happens when i have to support tools from different sources under the same API...
-    # TODO:  Rewrite FusedAdam to use multi-tensor apply and the same loss scaler.
-    if isinstance(optimizers, FP16_Optimizer_for_fused):
-        loss_scale = optimizers.cur_scale
-    else:
-        loss_scaler = _amp_state.loss_scalers[loss_id]
-        loss_scale = loss_scaler.loss_scale()
+    loss_scaler = _amp_state.loss_scalers[loss_id]
+    loss_scale = loss_scaler.loss_scale()
 
     if ((not _amp_state.opt_properties.master_weights)
         and (not loss_scaler.dynamic)
@@ -120,8 +113,8 @@ def scale_loss(loss,
         for optimizer in optimizers:
             optimizer._amp_stash.params_have_scaled_gradients = True
     else:
-        # FusedAdam and FusedSGD will take care of unscaling as part of their step() methods.
-        if not isinstance(optimizers, FP16_Optimizer_for_fused):
+        # FusedAdam and FusedSGD may take care of unscaling as part of their step() methods.
+        # if not isinstance(optimizers, FP16_Optimizer_for_fused):
             loss_scaler.clear_overflow_state()
             for optimizer in optimizers:
                 optimizer._post_amp_backward(loss_scaler)
@@ -142,10 +135,15 @@ def scale_loss(loss,
                                 maybe_print(("Gradient overflow.  Skipping step, loss scaler " +
                                              "{} reducing loss scale to {}").format(loss_id,
                                              loss_scaler.loss_scale()))
+                                # TODO:  I don't like the special casing for different optimizer implementations.
+                                # Maybe skip should delegate to a method owned by the optimizers themselves.
                                 if hasattr(opt._amp_stash, "all_fp32_from_fp16_params"):
                                     # Clear the master grads that wouldn't be zeroed by model.zero_grad()
                                     for param in opt._amp_stash.all_fp32_from_fp16_params:
                                         param.grad = None
+                                if hasattr(opt, "most_recent_scale"):
+                                    opt.most_recent_scale = 1.0
+                                    opt.scale_set_by_backward = False
                                 opt.step = opt_step
                                 opt._amp_stash.already_patched = False
                             return skip_step

apex/amp/scaler.py

@@ -16,7 +16,7 @@ def scale_check_overflow_python(model_grad, master_grad, scale, check_overflow=F
         master_grad.mul_(scale)
     return False
 
-def axpby_check_overflow_python(model_grad, stashed_grad, master_grad, scale, check_overflow=False):
+def axpby_check_overflow_python(model_grad, stashed_grad, master_grad, a, b, check_overflow=False):
     # Exception handling for 18.04 compatibility
     if check_overflow:
         cpu_sum = float(model_grad.float().sum())
@@ -26,9 +26,8 @@ def axpby_check_overflow_python(model_grad, stashed_grad, master_grad, scale, ch
     # if master_grad is not model_grad: # copy_ probably internally short-circuits this
     #     master_grad.copy_(model_grad)
     assert stashed_grad.dtype == master_grad.dtype
-    converted_model_grad = model_grad.to(master_grad.dtype)
-    stashed_grad.add_(scale, converted_model_grad)
-    master_grad.data = stashed_grad.data
+    converted_model_grad = model_grad.data.to(master_grad.dtype)
+    master_grad.data = a*converted_model_grad.data + b*stashed_grad.data
     return False
 
 class LossScaler(object):
@@ -92,11 +91,13 @@ class LossScaler(object):
                     break
 
     # unused_scale keeps some of the old API alive for hopefully a short time.
-    def unscale(self, model_grads, master_grads, unused_scale, models_are_masters=False):
+    def unscale(self, model_grads, master_grads, unused_scale, models_are_masters=False, scale_override=None):
         if self._has_overflow:
             return
 
         scale = self._loss_scale
+        if scale_override is not None:
+            scale = scale_override
 
         if scale == 1.0 and models_are_masters and not self.dynamic:
             return
@@ -126,7 +127,8 @@ class LossScaler(object):
                                     model_grads,
                                     stashed_master_grads,
                                     master_grads,
-                                    scale):
+                                    a,
+                                    b):
         for model, stashed, master in zip(model_grads, stashed_master_grads, master_grads):
             if model is None and stashed is None:
                 continue
@@ -141,7 +143,8 @@ class LossScaler(object):
                 self._has_overflow = axpby_check_overflow_python(model,
                                                                  stashed,
                                                                  master,
-                                                                 1./scale,
+                                                                 a,
+                                                                 b,
                                                                  self.dynamic)
                 if self._has_overflow and self.dynamic:
                     break
@@ -149,11 +152,14 @@ class LossScaler(object):
     def unscale_with_stashed(self,
                              model_grads,
                              stashed_master_grads,
-                             master_grads):
+                             master_grads,
+                             scale_override=None):
         if self._has_overflow:
             return
 
-        scale = self._loss_scale
+        grads_have_scale, stashed_have_scale, out_scale = self._loss_scale, 1.0, 1.0
+        if scale_override is not None:
+            grads_have_scale, stashed_have_scale, out_scale = scale_override
 
         if LossScaler.has_fused_kernel:
             if (not LossScaler.warned_unscaling_non_fp32_grad
@@ -167,14 +173,15 @@ class LossScaler(object):
             multi_tensor_applier(LossScaler.multi_tensor_axpby_cuda,
                                  self._overflow_buf,
                                  [model_grads, stashed_master_grads, master_grads],
-                                 1./scale,
-                                 1.0,
+                                 out_scale/grads_have_scale,   # 1./scale,
+                                 out_scale/stashed_have_scale, # 1.0,
                                  0) # check only arg 0, aka the incoming model grads, for infs
         else:
             self.unscale_with_stashed_python(model_grads,
                                              stashed_master_grads,
                                              master_grads,
-                                             scale)
+                                             out_scale/grads_have_scale,
+                                             out_scale/stashed_have_scale)
 
         # Defer to update_scale
         # If the fused kernel is available, we only need one D2H memcopy and sync.

apex/contrib/csrc/groupbn/batch_norm.cu

+#include <ATen/ATen.h>
+#include <ATen/cuda/CUDAContext.h>
+#include <THC/THCNumerics.cuh>
+
+#include "THC/THC.h"
+
+#include "batch_norm.h"
+
+#include <cuda.h>
+
+#define cudaCheckErrors(msg) \
+    do { \
+        cudaError_t __err = cudaGetLastError(); \
+        if (__err != cudaSuccess) { \
+            fprintf(stderr, "Fatal error: %s (%s at %s:%d)\n", \
+                msg, cudaGetErrorString(__err), \
+                __FILE__, __LINE__); \
+            fprintf(stderr, "*** FAILED - ABORTING\n"); \
+            exit(1); \
+        } \
+    } while (0)
+
+static size_t round_up_to_multiple(size_t x, int multiple) {
+  return ((x + multiple - 1) / multiple) * multiple;
+}
+
+// TODO: Stop manually allocating CUDA memory; allocate an ATen byte
+// tensor instead.
+struct Workspace {
+  Workspace(size_t size) : size(size), data(NULL) {
+    data = THCudaMalloc(at::globalContext().lazyInitCUDA(), size);
+  }
+  Workspace(const Workspace&) = delete;
+  Workspace(Workspace&&) = default;
+  Workspace& operator=(Workspace&&) = default;
+  ~Workspace() {
+    if (data) {
+      THCudaFree(at::globalContext().lazyInitCUDA(), data);
+    }
+  }
+
+  size_t size;
+  void* data;
+};
+
+// Return {y}
+at::Tensor nhwc_bn_fwd_train(
+                       const at::Tensor& x,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& minibatch_mean,
+                       const at::Tensor& minibatch_inv_var,
+                       const at::Tensor& ret_cta,
+                       const float momentum,
+                       const float epsilon,
+                       const bool fuse_relu,
+                       void * my_data,
+                       void * pair_data,
+                       void * pair_data2,
+                       void * pair_data3,
+                       const int bn_group,
+                       const at::Tensor& magic_tensor,
+                       const int occupancy,
+                       const int grid_dim_x,
+                       const bool coop) {
+
+  const int N = x.size(0);
+  const int H = x.size(1);
+  const int W = x.size(2);
+  const int C = x.size(3);
+
+  // generating new magic number and use that for sync
+  int* magic = magic_tensor.data<int>();
+  *magic = (*magic + 1) & 0xff;
+
+  // Allocate output tensor
+  at::Tensor y = at::empty({N, H, W, C}, x.options());
+
+  // Create wrapper
+  NhwcBatchNorm *bn = new NhwcBatchNorm();
+
+  bn->setInputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W, bn_group);
+  bn->setOutputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W);
+
+  bn->setConstants(momentum, epsilon);
+
+  // set pointers within the wrapper
+  bn->setInputOutputPointers(x.data<at::Half>(),
+                             nullptr,
+                             y.data<at::Half>(),
+                             nullptr);
+
+  bn->setWeightPointers({scale.data<float>(), bias.data<float>()}, {nullptr, nullptr});
+  bn->setParameterPointers({running_mean.data<float>(), running_inv_var.data<float>()});
+
+  // deal with workspace(s)
+  auto workspace_bytes = bn->numWorkspaceBytes();
+  // We'll create explicit tensors for the first 2 workspace ptrs, then allocate & offset
+  // an allocated workspace for the others
+  size_t total_workspace_bytes = 0;
+  std::vector<size_t> workspace_offsets;
+
+  for (auto index = 3; index < workspace_bytes.size(); ++index) {
+    total_workspace_bytes = round_up_to_multiple(total_workspace_bytes, 512);
+    workspace_offsets.push_back(total_workspace_bytes);
+
+    auto alloc_bytes = workspace_bytes[index];
+    total_workspace_bytes += alloc_bytes;
+  }
+
+  // Allocate the workspace
+  Workspace ws(total_workspace_bytes);
+
+  std::vector<void *> workspace;
+  workspace.push_back(minibatch_mean.data<float>());
+  workspace.push_back(minibatch_inv_var.data<float>());
+
+  auto stream = at::cuda::getCurrentCUDAStream().stream();
+  const int retired_cta_bytes = workspace_bytes[2];
+  void* retired_ctas = ret_cta.data<uint8_t>();
+  assert(ret_cta.size(0)>=retired_cta_bytes);
+  workspace.push_back(retired_ctas);
+
+  for (auto index = 3; index < workspace_bytes.size(); ++index) {
+    void *ptr = reinterpret_cast<uint8_t*>(ws.data) + workspace_offsets[index-3];
+    workspace.push_back(ptr);
+  }
+
+  bn->setWorkspacePointers(workspace, workspace_bytes);
+
+  // Don't fuse in ReLU for now at least
+  bn->fwd(stream, fuse_relu, my_data, pair_data, pair_data2, pair_data3, bn_group, *magic, occupancy, grid_dim_x, coop);
+
+  return y;
+}
+
+at::Tensor nhwc_bn_fwd_eval(
+                       const at::Tensor& x,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& ret_cta,
+                       const int bn_group,
+                       const float momentum,
+                       const float epsilon,
+                       const bool fuse_relu) {
+
+  const int N = x.size(0);
+  const int H = x.size(1);
+  const int W = x.size(2);
+  const int C = x.size(3);
+
+  // Allocate output tensor
+  at::Tensor y = at::empty({N, H, W, C}, x.options());
+
+  // Create wrapper
+  NhwcBatchNorm *bn = new NhwcBatchNorm();
+
+  bn->setInputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W, bn_group);
+  bn->setOutputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W);
+
+  bn->setConstants(momentum, epsilon);
+
+  // set pointers within the wrapper
+  bn->setInputOutputPointers(x.data<at::Half>(),
+                             nullptr,
+                             y.data<at::Half>(),
+                             nullptr);
+
+  bn->setWeightPointers({scale.data<float>(), bias.data<float>()}, {nullptr, nullptr});
+  bn->setParameterPointers({running_mean.data<float>(), running_inv_var.data<float>()});
+
+  // deal with workspace(s)
+  auto workspace_bytes = bn->numWorkspaceBytes();
+  // We'll create explicit tensors for the first 2 workspace ptrs, then allocate & offset
+  // an allocated workspace for the others
+  size_t total_workspace_bytes = 0;
+  std::vector<size_t> workspace_offsets;
+
+  for (auto index = 3; index < workspace_bytes.size(); ++index) {
+    total_workspace_bytes = round_up_to_multiple(total_workspace_bytes, 512);
+    workspace_offsets.push_back(total_workspace_bytes);
+
+    auto alloc_bytes = workspace_bytes[index];
+    total_workspace_bytes += alloc_bytes;
+  }
+
+  // Allocate the workspace
+  Workspace ws(total_workspace_bytes);
+
+  std::vector<void *> workspace;
+  workspace.push_back(nullptr);
+  workspace.push_back(nullptr);
+
+  auto stream = at::cuda::getCurrentCUDAStream().stream();
+  const int retired_cta_bytes = workspace_bytes[2];
+  void* retired_ctas = ret_cta.data<uint8_t>();
+  assert(ret_cta.size(0)>=retired_cta_bytes);
+  workspace.push_back(retired_ctas);
+
+  for (auto index = 3; index < workspace_bytes.size(); ++index) {
+    void *ptr = reinterpret_cast<uint8_t*>(ws.data) + workspace_offsets[index-3];
+    workspace.push_back(ptr);
+  }
+
+  bn->setWorkspacePointers(workspace, workspace_bytes);
+
+  // Don't fuse in ReLU for now at least
+  bn->fwdInference(stream, fuse_relu);
+
+  return y;
+
+}
+
+std::vector<at::Tensor> nhwc_bn_bwd(
+                       const at::Tensor& x,
+                       const at::Tensor& dy,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& minibatch_mean,
+                       const at::Tensor& minibatch_inv_var,
+                       const at::Tensor& ret_cta,
+                       const float momentum,
+                       const float epsilon,
+                       const bool fuse_relu,
+                       void * my_data,
+                       void * pair_data, 
+                       void * pair_data2, 
+                       void * pair_data3, 
+                       const int bn_group,
+                       const at::Tensor& magic_tensor,
+                       const int occupancy,
+                       const int grid_dim_x,
+                       const bool coop) {
+  // shape
+  const int N = x.size(0);
+  const int H = x.size(1);
+  const int W = x.size(2);
+  const int C = x.size(3);
+
+  // generating new magic number and use that for sync
+  int* magic = magic_tensor.data<int>();
+  *magic = (*magic + 1) & 0xff;
+
+  // outputs
+  at::Tensor x_grad, scale_grad, bias_grad;
+
+  // Allocate outputs
+  x_grad = at::empty_like(x);
+  scale_grad = at::empty_like(scale);
+  bias_grad = at::empty_like(bias);
+
+  // Create wrapper
+  NhwcBatchNorm *bn = new NhwcBatchNorm();
+
+  bn->setInputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W, bn_group);
+  bn->setOutputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W);
+
+  bn->setConstants(momentum, epsilon);
+
+  // set pointers within the wrapper
+  bn->setInputOutputPointers(x.data<at::Half>(),
+                             x_grad.data<at::Half>(),
+                             nullptr,
+                             dy.data<at::Half>());
+
+  bn->setWeightPointers({scale.data<float>(), bias.data<float>()}, {scale_grad.data<float>(), bias_grad.data<float>()});
+  bn->setParameterPointers({running_mean.data<float>(), running_inv_var.data<float>()});
+
+  // deal with workspace(s)
+  auto workspace_bytes = bn->numWorkspaceBytes();
+  // We'll create explicit tensors for the first 2 workspace ptrs, then allocate & offset
+  // an allocated workspace for the others
+  size_t total_workspace_bytes = 0;
+  std::vector<size_t> workspace_offsets;
+
+  for (auto index = 3; index < workspace_bytes.size(); ++index) {
+    total_workspace_bytes = round_up_to_multiple(total_workspace_bytes, 512);
+    workspace_offsets.push_back(total_workspace_bytes);
+
+    auto alloc_bytes = workspace_bytes[index];
+    total_workspace_bytes += alloc_bytes;
+  }
+
+  // Allocate the workspace
+  Workspace ws(total_workspace_bytes);
+
+  std::vector<void *> workspace;
+  workspace.push_back(minibatch_mean.data<float>());
+  workspace.push_back(minibatch_inv_var.data<float>());
+
+  auto stream = at::cuda::getCurrentCUDAStream().stream();
+  const int retired_cta_bytes = workspace_bytes[2];
+  void* retired_ctas = ret_cta.data<uint8_t>();
+  assert(ret_cta.size(0)>=retired_cta_bytes);
+  workspace.push_back(retired_ctas);
+
+  for (auto index = 3; index < workspace_bytes.size(); ++index) {
+    void *ptr = reinterpret_cast<uint8_t*>(ws.data) + workspace_offsets[index-3];
+    workspace.push_back(ptr);
+  }
+
+  bn->setWorkspacePointers(workspace, workspace_bytes);
+
+  bn->dgrad(stream, fuse_relu, my_data, pair_data, pair_data2, pair_data3, bn_group, *magic, occupancy, grid_dim_x, coop);
+
+  return std::vector<at::Tensor>{x_grad, scale_grad, bias_grad};
+}
+
+int nhwc_bn_fwd_occupancy() {
+    int device_id=-1;
+    cudaGetDevice(&device_id);
+
+    //max occupancy supported by the code is 2
+    return NhwcBatchNorm::smem_driven_fwd_occupancy(device_id, 2);
+}
+
+int nhwc_bn_bwd_occupancy() {
+    int device_id=-1;
+    cudaGetDevice(&device_id);
+    
+    //max occupancy supported by the code is 2
+    return NhwcBatchNorm::smem_driven_bwd_occupancy(device_id, 2);
+}
+
+

apex/contrib/csrc/groupbn/batch_norm_add_relu.cu

+#include <ATen/ATen.h>
+#include <ATen/cuda/CUDAContext.h>
+#include <THC/THCNumerics.cuh>
+
+#include "THC/THC.h"
+
+#include "batch_norm_add_relu.h"
+
+#include <cuda.h>
+
+//FIXME move the common stuff to common h file
+#define cudaCheckErrors(msg) \
+    do { \
+        cudaError_t __err = cudaGetLastError(); \
+        if (__err != cudaSuccess) { \
+            fprintf(stderr, "Fatal error: %s (%s at %s:%d)\n", \
+                msg, cudaGetErrorString(__err), \
+                __FILE__, __LINE__); \
+            fprintf(stderr, "*** FAILED - ABORTING\n"); \
+            exit(1); \
+        } \
+    } while (0)
+
+static size_t round_up_to_multiple(size_t x, int multiple) {
+  return ((x + multiple - 1) / multiple) * multiple;
+}
+
+// TODO: Stop manually allocating CUDA memory; allocate an ATen byte
+// tensor instead.
+struct Workspace {
+  Workspace(size_t size) : size(size), data(NULL) {
+    data = THCudaMalloc(at::globalContext().lazyInitCUDA(), size);
+  }
+  Workspace(const Workspace&) = delete;
+  Workspace(Workspace&&) = default;
+  Workspace& operator=(Workspace&&) = default;
+  ~Workspace() {
+    if (data) {
+      THCudaFree(at::globalContext().lazyInitCUDA(), data);
+    }
+  }
+
+  size_t size;
+  void* data;
+};
+
+// Return {y}
+at::Tensor nhwc_bn_addrelu_fwd_train(
+                       const at::Tensor& x,
+                       const at::Tensor& z,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& minibatch_mean,
+                       const at::Tensor& minibatch_inv_var,
+                       const at::Tensor& bitmask,
+                       const at::Tensor& ret_cta,
+                       const float momentum,
+                       const float epsilon,
+                       void * my_data,
+                       void * pair_data,
+                       void * pair_data2,
+                       void * pair_data3,
+                       const int bn_group,
+                       const at::Tensor& magic_tensor,
+                       const int occupancy,
+                       const int grid_dim_x,
+                       const bool coop) {
+
+  const int N = x.size(0);
+  const int H = x.size(1);
+  const int W = x.size(2);
+  const int C = x.size(3);
+
+  // generating new magic number and use that for sync
+  int* magic = magic_tensor.data<int>();
+  *magic = (*magic + 1) & 0xff;
+
+  // Allocate output tensor
+  at::Tensor y = at::empty({N, H, W, C}, x.options());
+
+  // Create wrapper
+  NhwcBatchNormAddRelu *bn = new NhwcBatchNormAddRelu();
+
+  bn->setInputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W, bn_group);
+  bn->setOutputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W);
+
+  bn->setConstants(momentum, epsilon);
+
+  // set pointers within the wrapper
+  bn->setInputOutputPointers(x.data<at::Half>(),
+                             nullptr,
+                             y.data<at::Half>(),
+                             nullptr,
+                             z.data<at::Half>(),
+                             nullptr);
+
+  bn->setWeightPointers({scale.data<float>(), bias.data<float>()}, {nullptr, nullptr});
+  bn->setParameterPointers({running_mean.data<float>(), running_inv_var.data<float>()});
+
+  // deal with workspace(s)
+  auto workspace_bytes = bn->numWorkspaceBytes();
+  // We'll create explicit tensors for the first 2 workspace ptrs, then allocate & offset
+  // an allocated workspace for the others
+  size_t total_workspace_bytes = 0;
+  std::vector<size_t> workspace_offsets;
+
+  for (auto index = 4; index < workspace_bytes.size(); ++index) {
+    total_workspace_bytes = round_up_to_multiple(total_workspace_bytes, 512);
+    workspace_offsets.push_back(total_workspace_bytes);
+
+    auto alloc_bytes = workspace_bytes[index];
+    total_workspace_bytes += alloc_bytes;
+  }
+
+  // Allocate the workspace
+  Workspace ws(total_workspace_bytes);
+
+  std::vector<void *> workspace;
+  workspace.push_back(minibatch_mean.data<float>());
+  workspace.push_back(minibatch_inv_var.data<float>());
+  workspace.push_back(bitmask.data<int32_t>());
+
+  auto stream = at::cuda::getCurrentCUDAStream().stream();
+  const int retired_cta_bytes = workspace_bytes[3];
+  void* retired_ctas = ret_cta.data<uint8_t>();
+  assert(ret_cta.size(0)>=retired_cta_bytes);
+
+  workspace.push_back(retired_ctas);
+
+  for (auto index = 4; index < workspace_bytes.size(); ++index) {
+    void *ptr = reinterpret_cast<uint8_t*>(ws.data) + workspace_offsets[index-4];
+    workspace.push_back(ptr);
+  }
+
+  bn->setWorkspacePointers(workspace, workspace_bytes);
+
+  // Don't fuse in ReLU for now at least
+  bn->fwd(stream, my_data, pair_data, pair_data2, pair_data3, bn_group, *magic, occupancy, grid_dim_x, coop);
+
+  return y;
+}
+
+at::Tensor nhwc_bn_addrelu_fwd_eval(
+                       const at::Tensor& x,
+                       const at::Tensor& z,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& ret_cta,
+                       const int bn_group,
+                       const float momentum,
+                       const float epsilon) {
+
+  const int N = x.size(0);
+  const int H = x.size(1);
+  const int W = x.size(2);
+  const int C = x.size(3);
+
+  // Allocate output tensor
+  at::Tensor y = at::empty({N, H, W, C}, x.options());
+
+  // Create wrapper
+  NhwcBatchNormAddRelu *bn = new NhwcBatchNormAddRelu();
+
+  bn->setInputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W, bn_group);
+  bn->setOutputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W);
+
+  bn->setConstants(momentum, epsilon);
+
+  // set pointers within the wrapper
+  bn->setInputOutputPointers(x.data<at::Half>(),
+                             nullptr,
+                             y.data<at::Half>(),
+                             nullptr,
+                             z.data<at::Half>(),
+                             nullptr);
+
+  bn->setWeightPointers({scale.data<float>(), bias.data<float>()}, {nullptr, nullptr});
+  bn->setParameterPointers({running_mean.data<float>(), running_inv_var.data<float>()});
+
+  // deal with workspace(s)
+  auto workspace_bytes = bn->numWorkspaceBytes();
+  // We'll create explicit tensors for the first 2 workspace ptrs, then allocate & offset
+  // an allocated workspace for the others
+  size_t total_workspace_bytes = 0;
+  std::vector<size_t> workspace_offsets;
+
+  for (auto index = 4; index < workspace_bytes.size(); ++index) {
+    total_workspace_bytes = round_up_to_multiple(total_workspace_bytes, 512);
+    workspace_offsets.push_back(total_workspace_bytes);
+
+    auto alloc_bytes = workspace_bytes[index];
+    total_workspace_bytes += alloc_bytes;
+  }
+
+  // Allocate the workspace
+  Workspace ws(total_workspace_bytes);
+
+  std::vector<void *> workspace;
+  workspace.push_back(nullptr);
+  workspace.push_back(nullptr);
+  workspace.push_back(nullptr);
+
+  auto stream = at::cuda::getCurrentCUDAStream().stream();
+  const int retired_cta_bytes = workspace_bytes[3];
+  void* retired_ctas = ret_cta.data<uint8_t>();
+  assert(ret_cta.size(0)>=retired_cta_bytes);
+  workspace.push_back(retired_ctas);
+
+  for (auto index = 4; index < workspace_bytes.size(); ++index) {
+    void *ptr = reinterpret_cast<uint8_t*>(ws.data) + workspace_offsets[index-4];
+    workspace.push_back(ptr);
+  }
+
+  bn->setWorkspacePointers(workspace, workspace_bytes);
+
+  // Don't fuse in ReLU for now at least
+  bn->fwdInference(stream);
+
+  return y;
+
+}
+
+std::vector<at::Tensor> nhwc_bn_addrelu_bwd(
+                       const at::Tensor& x,
+                       const at::Tensor& dy,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& minibatch_mean,
+                       const at::Tensor& minibatch_inv_var,
+                       const at::Tensor& bitmask,
+                       const at::Tensor& ret_cta,
+                       const float momentum,
+                       const float epsilon,
+                       void * my_data,
+                       void * pair_data, 
+                       void * pair_data2, 
+                       void * pair_data3, 
+                       const int bn_group,
+                       const at::Tensor& magic_tensor,
+                       const int occupancy,
+                       const int grid_dim_x,
+                       const bool coop) {
+  // shape
+  const int N = x.size(0);
+  const int H = x.size(1);
+  const int W = x.size(2);
+  const int C = x.size(3);
+
+  // generating new magic number and use that for sync
+  int* magic = magic_tensor.data<int>();
+  *magic = (*magic + 1) & 0xff;
+
+  // outputs
+  at::Tensor x_grad, z_grad, scale_grad, bias_grad;
+
+  // Allocate outputs
+  x_grad = at::empty_like(x);
+  z_grad = at::empty_like(x);
+  scale_grad = at::empty_like(scale);
+  bias_grad = at::empty_like(bias);
+
+  // Create wrapper
+  NhwcBatchNormAddRelu *bn = new NhwcBatchNormAddRelu();
+
+  bn->setInputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W, bn_group);
+  bn->setOutputDescriptor(CUDNN_TENSOR_NHWC, CUDNN_DATA_HALF, N, C, H, W);
+
+  bn->setConstants(momentum, epsilon);
+
+  // set pointers within the wrapper
+  bn->setInputOutputPointers(x.data<at::Half>(),
+                             x_grad.data<at::Half>(),
+                             nullptr,
+                             dy.data<at::Half>(),
+                             nullptr,
+                             z_grad.data<at::Half>());
+
+  bn->setWeightPointers({scale.data<float>(), bias.data<float>()}, {scale_grad.data<float>(), bias_grad.data<float>()});
+  bn->setParameterPointers({running_mean.data<float>(), running_inv_var.data<float>()});
+
+  // deal with workspace(s)
+  auto workspace_bytes = bn->numWorkspaceBytes();
+  // We'll create explicit tensors for the first 2 workspace ptrs, then allocate & offset
+  // an allocated workspace for the others
+  size_t total_workspace_bytes = 0;
+  std::vector<size_t> workspace_offsets;
+
+  for (auto index = 4; index < workspace_bytes.size(); ++index) {
+    total_workspace_bytes = round_up_to_multiple(total_workspace_bytes, 512);
+    workspace_offsets.push_back(total_workspace_bytes);
+
+    auto alloc_bytes = workspace_bytes[index];
+    total_workspace_bytes += alloc_bytes;
+  }
+
+  // Allocate the workspace
+  Workspace ws(total_workspace_bytes);
+
+  std::vector<void *> workspace;
+  workspace.push_back(minibatch_mean.data<float>());
+  workspace.push_back(minibatch_inv_var.data<float>());
+  workspace.push_back(bitmask.data<int32_t>());
+
+  auto stream = at::cuda::getCurrentCUDAStream().stream();
+  const int retired_cta_bytes = workspace_bytes[3];
+  void* retired_ctas = ret_cta.data<uint8_t>();
+  assert(ret_cta.size(0)>=retired_cta_bytes);
+  workspace.push_back(retired_ctas);
+
+  for (auto index = 4; index < workspace_bytes.size(); ++index) {
+    void *ptr = reinterpret_cast<uint8_t*>(ws.data) + workspace_offsets[index-4];
+    workspace.push_back(ptr);
+  }
+
+  bn->setWorkspacePointers(workspace, workspace_bytes);
+
+  bn->dgrad(stream, my_data, pair_data, pair_data2, pair_data3, bn_group, *magic, occupancy, grid_dim_x, coop);
+
+  return std::vector<at::Tensor>{x_grad, z_grad, scale_grad, bias_grad};
+}
+
+int nhwc_bn_addrelu_fwd_occupancy() {
+    int device_id=-1;
+    cudaGetDevice(&device_id);
+    
+    //max occupancy supported by the code is 2
+    return NhwcBatchNormAddRelu::smem_driven_fwd_occupancy(device_id, 2);
+}
+
+int nhwc_bn_addrelu_bwd_occupancy() {
+    int device_id=-1;
+    cudaGetDevice(&device_id);
+
+    //max occupancy supported by the code is 2
+    return NhwcBatchNormAddRelu::smem_driven_bwd_occupancy(device_id, 2);
+}
+

apex/contrib/csrc/groupbn/cuda_utils.h

+#include <ATen/cuda/CUDAContext.h>
+#ifndef CUDA_UTILS_H
+#define CUDA_UTILS_H
+
+namespace at {
+namespace cuda {
+
+namespace utils {
+
+static inline int MaxSharedMemoryPerMultiprocessor(int device_id) {
+    return getDeviceProperties(device_id)->sharedMemPerMultiprocessor;
+}
+
+
+}
+}
+}
+
+
+#endif

apex/contrib/csrc/groupbn/interface.cpp

+#include <pybind11/pybind11.h>
+#include <pybind11/numpy.h>
+#include <pybind11/stl.h>
+
+#include <torch/extension.h>
+#include <ATen/ATen.h>
+#include <ATen/ArrayRef.h>
+#include <ATen/ScalarType.h>
+#include "ATen/Scalar.h"
+#ifndef VERSION_GE_1_1
+#include "ATen/Type.h"
+#endif
+#include "ATen/Tensor.h"
+#include "ATen/Storage.h"
+#include "ATen/Generator.h"
+
+
+namespace py = pybind11;
+
+int64_t get_buffer_size(
+                       const int bn_sync_steps);
+
+void* get_data_ptr(
+                       const at::Tensor& data);
+
+void* get_remote_data_ptr(
+                       const at::Tensor& handle,
+                       const int64_t offset);
+
+void close_remote_data(
+                       const at::Tensor& handle);
+
+at::Tensor nhwc_bn_fwd_train(
+                       const at::Tensor& x,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& minibatch_mean,
+                       const at::Tensor& minibatch_inv_var,
+                       const at::Tensor& ret_cta,
+                       const float momentum,
+                       const float epsilon,
+                       const bool fuse_relu,
+                       void* my_data,
+                       void* pair_data,
+                       void* pair_data2,
+                       void* pair_data3,
+                       const int bn_group,
+                       const at::Tensor& magic_tensor,
+                       const int occupancy,
+                       const int grid_dim_x,
+                       const bool coop);
+
+at::Tensor nhwc_bn_fwd_eval(
+                       const at::Tensor& x,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& ret_cta,
+                       const int bn_group,
+                       const float momentum,
+                       const float epsilon,
+                       const bool fuse_relu);
+
+std::vector<at::Tensor> nhwc_bn_bwd(
+                       const at::Tensor& x,
+                       const at::Tensor& dy,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& minibatch_mean,
+                       const at::Tensor& minibatch_inv_var,
+                       const at::Tensor& ret_cta,
+                       const float momentum,
+                       const float epsilon,
+                       const bool fuse_relu,
+                       void* my_data,
+                       void* pair_data,
+                       void* pair_data2,
+                       void* pair_data3,
+                       const int bn_group,
+                       const at::Tensor& magic_tensor,
+                       const int occupancy,
+                       const int grid_dim_x,
+                       const bool coop);
+
+at::Tensor nhwc_bn_addrelu_fwd_train(
+                       const at::Tensor& x,
+                       const at::Tensor& z,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& minibatch_mean,
+                       const at::Tensor& minibatch_inv_var,
+                       const at::Tensor& bitmask,
+                       const at::Tensor& ret_cta,
+                       const float momentum,
+                       const float epsilon,
+                       void* my_data,
+                       void* pair_data,
+                       void* pair_data2,
+                       void* pair_data3,
+                       const int bn_group,
+                       const at::Tensor& magic_tensor,
+                       const int occupancy,
+                       const int grid_dim_x,
+                       const bool coop);
+
+at::Tensor nhwc_bn_addrelu_fwd_eval(
+                       const at::Tensor& x,
+                       const at::Tensor& z,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& ret_cta,
+                       const int bn_group,
+                       const float momentum,
+                       const float epsilon);
+
+std::vector<at::Tensor> nhwc_bn_addrelu_bwd(
+                       const at::Tensor& x,
+                       const at::Tensor& dy,
+                       const at::Tensor& scale,
+                       const at::Tensor& bias,
+                       const at::Tensor& running_mean,
+                       const at::Tensor& running_inv_var,
+                       const at::Tensor& minibatch_mean,
+                       const at::Tensor& minibatch_inv_var,
+                       const at::Tensor& bitmask,
+                       const at::Tensor& ret_cta,
+                       const float momentum,
+                       const float epsilon,
+                       void* my_data,
+                       void* pair_data,
+                       void* pair_data2,
+                       void* pair_data3,
+                       const int bn_group,
+                       const at::Tensor& magic_tensor,
+                       const int occupancy,
+                       const int grid_dim_x,
+                       const bool coop);
+
+int nhwc_bn_fwd_occupancy();
+int nhwc_bn_bwd_occupancy();
+
+int nhwc_bn_addrelu_fwd_occupancy();
+int nhwc_bn_addrelu_bwd_occupancy();
+
+PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
+
+  m.def("get_buffer_size", &get_buffer_size, "get_buffer_size");
+  m.def("get_data_ptr", &get_data_ptr, "get_data_ptr");
+  m.def("get_remote_data_ptr", &get_remote_data_ptr, "get_remote_data_ptr");
+  m.def("close_remote_data", &close_remote_data, "close_remote_data");
+
+  m.def("bn_fwd_nhwc", &nhwc_bn_fwd_train, "bn_fwd_nhwc");
+  m.def("bn_fwd_eval_nhwc", &nhwc_bn_fwd_eval, "bn_fwd_eval_nhwc");
+  m.def("bn_bwd_nhwc", &nhwc_bn_bwd, "bn_bwd_nhwc");
+
+  m.def("bn_fwd_nhwc_occupancy", &nhwc_bn_fwd_occupancy, "bn_fwd_nhwc_occupancy");
+  m.def("bn_bwd_nhwc_occupancy", &nhwc_bn_bwd_occupancy, "bn_bwd_nhwc_occupancy");
+
+  m.def("bn_addrelu_fwd_nhwc", &nhwc_bn_addrelu_fwd_train, "bn_addrelu_fwd_nhwc");
+  m.def("bn_addrelu_fwd_eval_nhwc", &nhwc_bn_addrelu_fwd_eval, "bn_addrelu_fwd_eval_nhwc");
+  m.def("bn_addrelu_bwd_nhwc", &nhwc_bn_addrelu_bwd, "bn_addrelu_bwd_nhwc");
+
+  m.def("bn_addrelu_fwd_nhwc_occupancy", &nhwc_bn_addrelu_fwd_occupancy, "bn_addrelu_fwd_nhwc_occupancy");
+  m.def("bn_addrelu_bwd_nhwc_occupancy", &nhwc_bn_addrelu_bwd_occupancy, "bn_addrelu_bwd_nhwc_occupancy");
+}
+

apex/contrib/csrc/groupbn/ipc.cu

+#include <ATen/ATen.h>
+#include <ATen/cuda/CUDAContext.h>
+#include <THC/THCNumerics.cuh>
+
+#include "THC/THC.h"
+
+#include <cuda.h>
+
+
+#define cudaCheckErrors(msg) \
+    do { \
+        cudaError_t __err = cudaGetLastError(); \
+        if (__err != cudaSuccess) { \
+            fprintf(stderr, "Fatal error: %s (%s at %s:%d)\n", \
+                msg, cudaGetErrorString(__err), \
+                __FILE__, __LINE__); \
+            fprintf(stderr, "*** FAILED - ABORTING\n"); \
+            exit(1); \
+        } \
+    } while (0)
+
+template<>
+struct std::hash<cudaIpcMemHandle_t> {
+  size_t operator() (const cudaIpcMemHandle_t& handle) const {
+    size_t hash = 0;
+    uint8_t* ptr = (uint8_t*)&handle;
+    assert(sizeof(uint8_t) == 1);
+    for (int i=0; i<sizeof(cudaIpcMemHandle_t); i++) {
+      hash += *ptr;
+      ptr++;
+    }
+    return hash;
+  }
+};
+
+template<>
+struct std::equal_to<cudaIpcMemHandle_t> {
+  bool operator() (const cudaIpcMemHandle_t &lhs,
+                             const cudaIpcMemHandle_t &rhs) const {
+    return (std::memcmp((void*) &lhs,
+                        (void*) &rhs,
+                        sizeof(cudaIpcMemHandle_t)) == 0);
+  }
+};
+
+namespace {
+
+namespace gpuipc {
+//from: src/operator/nn/cudnn/nhwc_batch_norm_kernel.h
+// The number of threads per pixel.
+const int THREADS_PER_PIXEL = 16;
+// The number of elements per ldg.
+const int ELEMENTS_PER_LDG = 4;
+// The number of reducing ops, each uses its own space : mean, var, dscale, dbias
+const int REDUCE_OPS = 4;
+// Maximum block.y supported - limited due to buffer allocation
+const int MAX_BLOCK_Y = 256;
+const int MAX_OFFSET = REDUCE_OPS*MAX_BLOCK_Y;
+const int BYTES_PER_ELEM = 4;
+// Buffer size per sync step
+const int SINGLE_SYNC_BUFFER_BYTES = MAX_OFFSET*THREADS_PER_PIXEL*2*ELEMENTS_PER_LDG*BYTES_PER_ELEM;
+};
+
+class IpcMemHandleRegistry {
+public:
+  void* getPtr(const cudaIpcMemHandle_t& handle, int64_t offset) {
+    if (registry_.count(handle) == 0) {
+      registry_.insert(std::make_pair(handle, RegistryEntry()));
+      registry_[handle].dev_ptr = ipcOpenMem(handle);
+    }
+    registry_[handle].ref_count++;
+    return (((uint8_t*)registry_[handle].dev_ptr) + offset);
+  }
+
+  void releasePtr(const cudaIpcMemHandle_t& handle) {
+    if (registry_.count(handle) == 0) {
+    }
+    if (--registry_[handle].ref_count == 0) {
+      ipcCloseMem(registry_[handle].dev_ptr);
+      registry_.erase(handle);
+    }
+  }
+
+  struct RegistryEntry {
+    void* dev_ptr;
+    int   ref_count;
+    RegistryEntry() : dev_ptr(NULL) , ref_count(0) {}
+  };
+
+protected:
+  std::unordered_map<cudaIpcMemHandle_t, RegistryEntry> registry_;
+
+  void* ipcOpenMem(const cudaIpcMemHandle_t& handle) {
+    void *data;
+    cudaIpcOpenMemHandle(&data, handle, cudaIpcMemLazyEnablePeerAccess);
+    cudaCheckErrors("ipc init");
+    return data;
+  }
+
+  void ipcCloseMem(void* dev_ptr) {
+    cudaIpcCloseMemHandle(dev_ptr);
+    cudaCheckErrors("ipc close");
+  }
+
+};
+
+}
+
+static IpcMemHandleRegistry ipc_mem_registry;
+
+int64_t get_buffer_size(const int bn_sync_steps) {
+  return bn_sync_steps * gpuipc::SINGLE_SYNC_BUFFER_BYTES;
+}
+
+void* get_remote_data_ptr(const at::Tensor& handle, const int64_t offset) {
+  cudaIpcMemHandle_t my_handle;
+  memcpy((unsigned char *)(&my_handle), handle.data<uint8_t>(), sizeof(my_handle));
+  return ipc_mem_registry.getPtr(my_handle, offset);
+}
+
+void close_remote_data(const at::Tensor& handle) {
+    cudaIpcMemHandle_t my_handle;
+    memcpy((unsigned char *)(&my_handle), handle.data<uint8_t>(), sizeof(my_handle));
+  ipc_mem_registry.releasePtr(my_handle);
+}
+
+void* get_data_ptr(
+                   const at::Tensor& data) {
+  return data.data<uint8_t>();
+}

apex/contrib/csrc/xentropy/interface.cpp

+#include <torch/extension.h>
+
+// CUDA forward declarations
+
+std::vector<at::Tensor> softmax_xentropy_cuda(
+    const at::Tensor &input,
+    const at::Tensor &labels,
+    const float smoothing,
+    const bool half_to_float);
+
+at::Tensor softmax_xentropy_backward_cuda(
+    const at::Tensor &grad_loss,
+    const at::Tensor &logits,
+    const at::Tensor &max_log_sum_exp,
+    const at::Tensor &labels,
+    const float smoothing);
+
+// C++ interface
+
+#define CHECK_CUDA(x) AT_ASSERTM(x.type().is_cuda(), #x " must be a CUDA tensor")
+#define CHECK_CONTIGUOUS(x) AT_ASSERTM(x.is_contiguous(), #x " must be contiguous")
+#define CHECK_INPUT(x) CHECK_CUDA(x); CHECK_CONTIGUOUS(x)
+
+std::vector<at::Tensor> softmax_xentropy_forward(
+    const at::Tensor &input,
+    const at::Tensor &labels,
+    const float smoothing,
+    const bool half_to_float) {
+    CHECK_CUDA(input);
+    CHECK_INPUT(labels);
+
+    return softmax_xentropy_cuda(input, labels, smoothing, half_to_float);
+}
+
+at::Tensor softmax_xentropy_backward(
+    const at::Tensor &grad_loss,
+    const at::Tensor &logits,
+    const at::Tensor &max_log_sum_exp,
+    const at::Tensor &labels,
+    const float smoothing)  {
+    CHECK_CUDA(grad_loss);
+    CHECK_CUDA(logits);
+    CHECK_INPUT(max_log_sum_exp);
+    CHECK_INPUT(labels);
+
+    return softmax_xentropy_backward_cuda(grad_loss, logits, max_log_sum_exp, labels, smoothing);
+}
+
+PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
+    m.def("forward", &softmax_xentropy_forward, "Softmax cross entropy loss with label smoothing forward (CUDA)");
+    m.def("backward", &softmax_xentropy_backward, "Softmax cross entropy loss with label smoothing backward (CUDA)");
+}

apex/contrib/groupbn/__init__.py

+try:
+    import torch
+    import bnp
+    from .batch_norm import BatchNorm2d_NHWC
+    del torch
+    del bnp
+    del batch_norm
+except ImportError as err:
+    print("apex was installed without --bnp flag, contrib.groupbn is not available")

apex/contrib/groupbn/batch_norm.py

+import torch
+import numpy as np
+from torch.nn.modules.batchnorm import _BatchNorm
+
+import bnp
+
+class bn_NHWC_impl(torch.autograd.Function):
+    @staticmethod
+    def forward(ctx, x, s, b, rm, riv, mini_m, mini_riv, ret_cta, mom, epsilon, fuse_relu, is_train, bn_group, my_data, pair_data, magic, pair_data2, pair_data3, fwd_occup, fwd_grid_x, bwd_occup, bwd_grid_x, multi_stream):
+        if is_train:
+            ctx.save_for_backward(x, s, b, rm, riv, mini_m, mini_riv)
+            ctx.epsilon = epsilon
+            ctx.momentum = mom
+            ctx.ret_cta = ret_cta
+            ctx.fuse_relu = fuse_relu
+            ctx.my_data = my_data
+            ctx.pair_data = pair_data
+            ctx.magic = magic
+            ctx.pair_data2 = pair_data2
+            ctx.pair_data3 = pair_data3
+            ctx.bn_group = bn_group
+            ctx.bwd_occup = bwd_occup
+            ctx.bwd_grid_x = bwd_grid_x
+            ctx.multi_stream = multi_stream
+
+            res =  bnp.bn_fwd_nhwc(x, s, b, rm, riv, mini_m, mini_riv, ret_cta, mom, epsilon, fuse_relu, my_data, pair_data, pair_data2, pair_data3, bn_group, magic, fwd_occup, fwd_grid_x, multi_stream)
+            return res
+        else:
+            return bnp.bn_fwd_eval_nhwc(x, s, b, rm, riv, ret_cta, bn_group, mom, epsilon, fuse_relu)
+
+    @staticmethod
+    def backward(ctx, grad_y):
+        x, s, b, rm, riv, mini_m, mini_riv = ctx.saved_variables
+        epsilon = ctx.epsilon
+        mom = ctx.momentum
+        ret_cta = ctx.ret_cta
+        fuse_relu = ctx.fuse_relu
+        my_data = ctx.my_data
+        pair_data = ctx.pair_data
+        magic = ctx.magic
+        pair_data2 = ctx.pair_data2
+        pair_data3 = ctx.pair_data3
+        bn_group = ctx.bn_group
+        bwd_occup = ctx.bwd_occup
+        bwd_grid_x = ctx.bwd_grid_x
+        multi_stream = ctx.multi_stream
+
+        dx, dscale, dbias = bnp.bn_bwd_nhwc(x, grad_y, s, b, rm, riv, mini_m, mini_riv, ret_cta, mom, epsilon, fuse_relu, my_data, pair_data, pair_data2, pair_data3, bn_group, magic, bwd_occup, bwd_grid_x, multi_stream)
+
+        return dx, dscale, dbias, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None
+
+
+class bn_addrelu_NHWC_impl(torch.autograd.Function):
+    @staticmethod
+    def forward(ctx, x, z, s, b, rm, riv, mini_m, mini_riv, grid_dim_y, ret_cta, mom, epsilon, is_train, bn_group, my_data, pair_data, magic, pair_data2, pair_data3, fwd_occup, fwd_grid_x, bwd_occup, bwd_grid_x, multi_stream):
+        if is_train:
+            bitmask = torch.cuda.IntTensor(((x.numel()+31)//32) * 2 * grid_dim_y)
+            ctx.save_for_backward(x, s, b, rm, riv, mini_m, mini_riv, bitmask)
+            ctx.epsilon = epsilon
+            ctx.momentum = mom
+            ctx.ret_cta = ret_cta
+            ctx.my_data = my_data
+            ctx.pair_data = pair_data
+            ctx.magic = magic
+            ctx.pair_data2 = pair_data2
+            ctx.pair_data3 = pair_data3
+            ctx.bn_group = bn_group
+            ctx.bwd_occup = bwd_occup
+            ctx.bwd_grid_x = bwd_grid_x
+            ctx.multi_stream = multi_stream
+
+            res =  bnp.bn_addrelu_fwd_nhwc(x, z, s, b, rm, riv, mini_m, mini_riv, bitmask, ret_cta, mom, epsilon, my_data, pair_data, pair_data2, pair_data3, bn_group, magic, fwd_occup, fwd_grid_x, multi_stream)
+            return res
+        else:
+            return bnp.bn_addrelu_fwd_eval_nhwc(x, z, s, b, rm, riv, ret_cta, bn_group, mom, epsilon)
+
+    @staticmethod
+    def backward(ctx, grad_y):
+        x, s, b, rm, riv, mini_m, mini_riv, bitmask = ctx.saved_variables
+        epsilon = ctx.epsilon
+        mom = ctx.momentum
+        ret_cta = ctx.ret_cta
+        my_data = ctx.my_data
+        pair_data = ctx.pair_data
+        magic = ctx.magic
+        pair_data2 = ctx.pair_data2
+        pair_data3 = ctx.pair_data3
+        bn_group = ctx.bn_group
+        bwd_occup = ctx.bwd_occup
+        bwd_grid_x = ctx.bwd_grid_x
+        multi_stream = ctx.multi_stream
+
+        dx, dz, dscale, dbias = bnp.bn_addrelu_bwd_nhwc(x, grad_y, s, b, rm, riv, mini_m, mini_riv, bitmask, ret_cta, mom, epsilon, my_data, pair_data, pair_data2, pair_data3, bn_group, magic, bwd_occup, bwd_grid_x, multi_stream)
+
+        return dx, dz, dscale, dbias, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None
+
+
+
+
+
+class BatchNorm2d_NHWC(_BatchNorm):
+    # if using BatchNorm2d_NHWC simultaneously with multiple streams set multi_stream to True
+    def __init__(self, num_features, fuse_relu=False, bn_group=1, max_cta_per_sm=2, cta_launch_margin=12, multi_stream=False):
+        super(BatchNorm2d_NHWC, self).__init__(num_features)
+
+        self.fuse_relu = fuse_relu
+        self.multi_stream = multi_stream
+
+        self.minibatch_mean = torch.cuda.FloatTensor(num_features)
+        self.minibatch_riv = torch.cuda.FloatTensor(num_features)
+
+        #defaut to distributed bn disabled
+        self.bn_group = bn_group
+        self.max_cta_per_sm = max_cta_per_sm        #used only in training fwd and bwd
+        self.cta_launch_margin = cta_launch_margin  #used only in training fwd and bwd
+        self.my_data = None
+        self.pair_data = None
+        self.pair_data2 = None
+        self.pair_data3 = None
+        self.local_rank = 0
+        self.magic = torch.IntTensor([0])
+
+        #calculate cta per sm occupancies
+        assert(max_cta_per_sm>0) # won't be able to do much with 0 CTAs :)
+        self.fwd_occupancy =  min(bnp.bn_fwd_nhwc_occupancy(), max_cta_per_sm)
+        self.bwd_occupancy =  min(bnp.bn_bwd_nhwc_occupancy(), max_cta_per_sm)
+        self.addrelu_fwd_occupancy =  min(bnp.bn_addrelu_fwd_nhwc_occupancy(), max_cta_per_sm)
+        self.addrelu_bwd_occupancy =  min(bnp.bn_addrelu_bwd_nhwc_occupancy(), max_cta_per_sm)
+
+        #calculate grid dimentions based on occupancy numbers
+        mp_count = torch.cuda.get_device_properties(None).multi_processor_count
+        self.fwd_grid_dim_x = max(mp_count*self.fwd_occupancy - cta_launch_margin , 1)
+        self.bwd_grid_dim_x = max(mp_count*self.bwd_occupancy - cta_launch_margin , 1)
+        self.addrelu_fwd_grid_dim_x = max(mp_count*self.addrelu_fwd_occupancy - cta_launch_margin , 1)
+        self.addrelu_bwd_grid_dim_x = max(mp_count*self.addrelu_bwd_occupancy - cta_launch_margin , 1)
+        self.grid_dim_y = (num_features + 63) // 64
+
+        # allocate scratch space used by implementation
+        # TODO: scratch space that is not supposed to be exposed at user code. We only need one time initialization, the
+        # same buffer could be reused in future iterations. Currently we exposed it here instead of requesting new
+        # buffer from cache allocator to avoid unnecessary initialization at future iterations.
+        self.ret_cta = torch.cuda.ByteTensor(8192).fill_(0)
+
+        #FIXME: turn pair handles into an array
+        if bn_group>1:
+            local_rank = torch.distributed.get_rank()
+            world_size = torch.distributed.get_world_size()          
+            assert(world_size >= bn_group)
+            assert(world_size % bn_group == 0)
+         
+            bn_sync_steps = 1
+            if (bn_group==4):
+                bn_sync_steps = 2
+            if (bn_group==8):
+                bn_sync_steps = 3
+
+            self.ipc_buffer = torch.cuda.ByteTensor(bnp.get_buffer_size(bn_sync_steps))
+            self.my_data = bnp.get_data_ptr(self.ipc_buffer)
+            # we are walking on very thin ice here by utilizing internal `_share_cuda_()`
+            self.storage = self.ipc_buffer.storage()
+            self.share_cuda = self.storage._share_cuda_()
+            internal_cuda_mem = self.share_cuda
+            # internal_cuda_mem[1]: ipc_mem_handle
+            my_handle = torch.cuda.ByteTensor(np.frombuffer(internal_cuda_mem[1], dtype=np.uint8))
+            # internal_cuda_mem[3]: offset
+            my_offset = torch.cuda.IntTensor([internal_cuda_mem[3]])
+
+            handles_all = torch.empty(world_size, my_handle.size(0), dtype=my_handle.dtype, device=my_handle.device)
+            handles_l = list(handles_all.unbind(0))
+            torch.distributed.all_gather(handles_l, my_handle)
+
+            offsets_all = torch.empty(world_size, my_offset.size(0), dtype=my_offset.dtype, device=my_offset.device)
+            offsets_l = list(offsets_all.unbind(0))
+            torch.distributed.all_gather(offsets_l, my_offset)
+
+            #whom do I actually care about? that would be local_rank XOR 1
+            self.pair_handle = handles_l[local_rank ^ 1].cpu().contiguous()
+            pair_offset = offsets_l[local_rank ^ 1].cpu()
+            self.pair_data = bnp.get_remote_data_ptr(self.pair_handle, pair_offset)
+
+            if bn_group>2:
+                self.pair_handle2 = handles_l[local_rank ^ 2].cpu().contiguous()
+                pair_offset2 = offsets_l[local_rank ^ 2].cpu()
+                self.pair_data2 = bnp.get_remote_data_ptr(self.pair_handle2, pair_offset2)
+
+            if bn_group>4:
+                self.pair_handle3 = handles_l[local_rank ^ 4].cpu().contiguous()
+                pair_offset3 = offsets_l[local_rank ^ 4].cpu()
+                self.pair_data3 = bnp.get_remote_data_ptr(self.pair_handle3, pair_offset3)
+
+            #FIXME: get magic value into C code and eliminate from here
+            self.magic = torch.IntTensor([2])
+            self.local_rank = local_rank
+
+
+    def forward(self, x, z=None):
+        if z is not None:
+            assert(self.fuse_relu==True)
+            return bn_addrelu_NHWC_impl.apply(x, z,
+                                  self.weight, self.bias,
+                                  self.running_mean, self.running_var,
+                                  self.minibatch_mean, self.minibatch_riv, self.grid_dim_y, self.ret_cta,
+                                  self.momentum,
+                                  self.eps, self.training, self.bn_group, self.my_data, self.pair_data, (self.magic), self.pair_data2, self.pair_data3,
+                                  self.addrelu_fwd_occupancy, self.addrelu_fwd_grid_dim_x,
+                                  self.addrelu_bwd_occupancy, self.addrelu_bwd_grid_dim_x,
+                                  self.multi_stream)
+        else:
+            return bn_NHWC_impl.apply(x,
+                                  self.weight, self.bias,
+                                  self.running_mean, self.running_var,
+                                  self.minibatch_mean, self.minibatch_riv, self.ret_cta,
+                                  self.momentum,
+                                  self.eps, self.fuse_relu, self.training, self.bn_group, self.my_data, self.pair_data, (self.magic), self.pair_data2, self.pair_data3,
+                                  self.fwd_occupancy, self.fwd_grid_dim_x,
+                                  self.bwd_occupancy, self.bwd_grid_dim_x,
+                                  self.multi_stream)
+
+    def __del__(self):
+        if self.bn_group>1:
+          bnp.close_remote_data(self.pair_handle)
+          if self.bn_group>2:
+              bnp.close_remote_data(self.pair_handle2)
+              if self.bn_group>4:
+                 bnp.close_remote_data(self.pair_handle3)

apex/contrib/test/test_label_smoothing.py

+import torch
+from apex.contrib import xentropy as label_smoothing
+import unittest
+
+import warnings
+import random
+import numpy as np
+import time
+
+def label_smoothing_raw(x, target, padding_idx, smoothing):
+    logprobs = torch.nn.functional.log_softmax(x, dim=-1, dtype=torch.float32)
+
+    non_pad_mask = (target != padding_idx)
+    nll_loss = -logprobs.gather(dim=-1, index=target.unsqueeze(1))
+    nll_loss = nll_loss.squeeze(1)[non_pad_mask]
+    smooth_loss = -logprobs.mean(dim=-1)[non_pad_mask]
+    loss = (1.0 - smoothing) * nll_loss + smoothing * smooth_loss
+    return loss
+
+def label_smoothing_opt_1(x, target, padding_idx, smoothing):
+    logprobs = torch.nn.functional.log_softmax(x, dim=-1, dtype=torch.float32)
+
+    pad_mask = (target == padding_idx)
+    ll_loss = logprobs.gather(dim=-1, index=target.unsqueeze(1)).squeeze(1)
+    smooth_loss = logprobs.mean(dim=-1)
+    loss = (smoothing - 1.0) * ll_loss - smoothing * smooth_loss
+    loss.masked_fill_(pad_mask, 0)
+    return loss
+
+class LabelSmoothingTest(unittest.TestCase):
+    def setUp(self, seed=1234):
+        random.seed(seed)
+        np.random.seed(seed)
+        torch.manual_seed(seed)
+        torch.cuda.manual_seed_all(seed)
+
+        # Set pytorch print precision
+        torch.set_printoptions(precision=10)
+
+    def gen_test_inputs(self, N, T, H, smoothing, padding_idx):
+        logits = torch.randn((N*T, H), dtype=torch.half, device='cuda',
+            requires_grad=True)
+        labels = torch.randint(0, H, [N*T], device='cuda')
+        for i in random.sample(range(N*T), N*T//6):
+            labels[i] = padding_idx
+        half_to_float = (logits.dtype == torch.half)
+
+        return logits, labels, half_to_float
+
+    def print_max_diff_elem(self, ref, tst):
+        ref, tst = ref.flatten(), tst.flatten()
+        diff = (ref - tst).abs().max()
+        idx = (ref - tst).abs().argmax()
+        print("Max atol idx: {}, diff: {:.6f}, ref: {:.6f}, tst: {:.6f}".format(
+            idx, diff, ref[idx], tst[idx]))
+
+    def test_label_smoothing_function(self):
+        # Set label smoothing configuration
+        smoothing, padding_idx = 0.1, 0
+        N, T, H = 128, 74, 32320
+        iters = 10
+        loss_func = label_smoothing.SoftmaxCrossEntropyLoss.apply
+
+        for i in range(iters):
+            logits, labels, half_to_float = self.gen_test_inputs(
+                N, T, H, smoothing, padding_idx)
+    
+            # Run original softmax cross entropy with label smoothing
+            logits.grad = None
+            losses = label_smoothing_raw(logits, labels, padding_idx, smoothing)
+            loss = losses.sum()
+            loss.backward()
+            
+            ref_loss = loss.clone().detach()
+            ref_grad = logits.grad.clone().detach()
+
+            # Run optimized softmax cross entropy with label smoothing
+            logits.grad = None
+            losses = loss_func(logits, labels, smoothing, padding_idx, half_to_float)
+            loss = losses.sum()
+            loss.backward()
+
+            val_loss = loss.clone().detach()
+            val_grad = logits.grad.clone().detach()
+
+            # Validate
+            self.print_max_diff_elem(ref_grad, val_grad)
+            self.assertTrue(torch.allclose(ref_loss, val_loss, atol=1e-5, rtol=1e-5))
+            self.assertTrue(torch.allclose(ref_grad, val_grad, atol=1e-5, rtol=1e-5))
+
+    def test_label_smoothing_perf(self):
+        # Set label smoothing configuration
+        smoothing, padding_idx = 0.1, 0
+        N, T, H = 128, 74, 32320
+        iters = 1000
+        loss_func = label_smoothing.SoftmaxCrossEntropyLoss.apply
+        print()
+
+        logits, labels, half_to_float = self.gen_test_inputs(
+            N, T, H, smoothing, padding_idx)
+    
+        # Run original softmax cross entropy with label smoothing
+        torch.cuda.synchronize()
+        ts = time.time()
+        for i in range(iters):
+            logits.grad = None
+            losses = label_smoothing_raw(logits, labels, padding_idx, smoothing)
+            loss = losses.sum() / N
+            loss.backward()
+        torch.cuda.synchronize()
+        print("Raw time {:.2f} s elapsed for {} iterations, norm {:.4f}".format(
+            time.time() - ts, iters, logits.grad.norm()))
+            
+        # Run optimized softmax cross entropy with label smoothing
+        torch.cuda.synchronize()
+        ts = time.time()
+        for i in range(iters):
+            logits.grad = None
+            losses = loss_func(logits, labels, smoothing, padding_idx, half_to_float)
+            loss = losses.sum() / N
+            loss.backward()
+        torch.cuda.synchronize()
+        print("Opt time {:.2f} s elapsed for {} iterations, norm {:.4f}".format(
+            time.time() - ts, iters, logits.grad.norm()))
+
+if __name__ == '__main__':
+    unittest.main()
+

apex/contrib/xentropy/__init__.py

+try:
+    import torch
+    import xentropy_cuda
+    from .softmax_xentropy import SoftmaxCrossEntropyLoss
+    del torch
+    del xentropy_cuda
+    del softmax_xentropy
+except ImportError as err:
+    print("apex was installed without --xentropy flag, contrib.xentropy is not available")