feat(mge/quant): add TQT quant method

GitOrigin-RevId: 00b1616e73ed34c8c09e2407b8fc7d90230f8cec

python_module/megengine/core/function.py

@@ -154,6 +154,7 @@ class Function(metaclass=ABCMeta):
         memo[id(self)] = result
         for k, v in self.__dict__.items():
             setattr(result, k, copy.deepcopy(v, memo))
+        setattr(result, "saved_tensors", tmp)
         self.saved_tensors = tmp
         return result
 

python_module/megengine/module/qat/module.py

@@ -77,13 +77,19 @@ class QATModule(Module):
         r"""
         Get weight's quantization dtype as the method from ``qconfig``.
         """
-        return self.weight_observer.get_dtype()
+        if hasattr(self.act_fake_quant, "get_dtype"):
+            return self.weight_fake_quant.get_dtype()
+        else:
+            return self.weight_observer.get_dtype()
 
     def get_activation_dtype(self):
         r"""
         Get activation's quantization dtype as the method from ``qconfig``.
         """
-        return self.act_observer.get_dtype()
+        if hasattr(self.act_fake_quant, "get_dtype"):
+            return self.act_fake_quant.get_dtype()
+        else:
+            return self.act_observer.get_dtype()
 
     @classmethod
     @abstractmethod

python_module/megengine/quantization/__init__.py

@@ -12,4 +12,5 @@ from .qconfig import (
     calibration_qconfig,
     ema_fakequant_qconfig,
     min_max_fakequant_qconfig,
+    tqt_quant_qconfig,
 )

python_module/megengine/quantization/fake_quant.py

@@ -5,17 +5,20 @@
 # Unless required by applicable law or agreed to in writing,
 # software distributed under the License is distributed on an
 # "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+import copy
+import math
+
+import numpy as np
+
 from .. import functional as F
-from .._internal.dtype import _metadata_dict
+from .._internal.dtype import _metadata_dict, get_quantized_dtype
+from ..core import Buffer, Function, Parameter
+from ..jit import sideeffect
 from ..module import Module
 from .observer import ObserverMode, Round
 
 
-class FakeQuantize(Module):
-    r"""
-    A module to do quant and dequant according to observer's scale and zero_point.
-    """
-
+class _FakeQuantize(Module):
     def __init__(self, dtype: str, enable: bool = True):
         super().__init__()
         if not dtype in _metadata_dict.keys():
@@ -35,25 +38,103 @@ class FakeQuantize(Module):
     def disable(self):
         self.enabled = False
 
+    def fake_quant_forward(self, inp, q_dict):
+        return inp
+
+    def normal_foward(self, inp, q_dict):
+        return inp
+
     def forward(self, inp, q_dict):
         if self.enabled:
-            if q_dict["mode"] == ObserverMode.SYMMERTIC:
-                scale = q_dict["scale"]
-                # Quant
-                oup = Round()(inp / scale)
-                # clip
-                oup = F.minimum(F.maximum(oup, self.qmin), self.qmax)
-                # DeQuant
-                oup = (oup) * scale
-                return oup
-            else:
-                scale = q_dict["scale"]
-                zero_point = q_dict["zero_point"]
-                # Quant
-                oup = Round()(inp / scale) + zero_point
-                # clip
-                oup = F.minimum(F.maximum(oup, self.qmin), self.qmax)
-                # DeQuant
-                oup = (oup - zero_point) * scale
-                return oup
+            return self.fake_quant_forward(inp, q_dict)
+        else:
+            return self.normal_foward(inp, q_dict)
+
+
+class TQT_Function(Function):
+    def __init__(self, lowerbound, upperbound):
+        super().__init__()
+        self.lowerbound = lowerbound
+        self.upperbound = upperbound
+
+    def forward(self, inp, scale):
+        t = 2 ** scale
+        # t = F.maximum(t, 1e-4)
+        inp_scaled = inp / t
+        inp_clipped = F.maximum(F.minimum(inp_scaled, self.upperbound), self.lowerbound)
+        inp_rounded = F.round(inp_clipped)
+        inp_flq = inp_rounded * t
+        self.save_for_backward(inp_scaled, inp_rounded, t)
+        return inp_flq
+
+    def backward(self, grad_inp_flq):
+        (inp_scaled, inp_rounded, t) = self.saved_tensors
+        mask_clip = (inp_scaled < -0.5 + self.lowerbound) + (
+            inp_scaled > self.upperbound + 0.5
+        )  # mask for accumulating the gradients of |data_scaled|>L
+        mask_quant = F.abs(
+            mask_clip - 1
+        )  # mask for accumulating the gradients with |data_scaled|<=L
+        grad_quant = (
+            grad_inp_flq * mask_quant * (inp_rounded - inp_scaled)
+        )  # gradient within |data_scaled|<=L
+        grad_clip = (
+            grad_inp_flq * mask_clip * inp_rounded
+        )  # gradient with   | data_scaled|>L
+        grad_s = grad_clip.sum() + grad_quant.sum()
+        # dL/ds = dL/dt * t * ln(2)
+        grad_s = grad_s * t * math.log(2)
+        grad_inp = grad_inp_flq * mask_quant
+        return grad_inp, grad_s
+
+
+class TQT(_FakeQuantize):
+    """
+    TQT: https://arxiv.org/abs/1903.08066 Trained Quantization Thresholds 
+    for Accurate and Efficient Fixed-Point Inference of Deep Neural Networks
+    """
+
+    def __init__(self, dtype: str, enable: bool = True):
+        super().__init__(dtype, enable)
+        self.scale = Parameter(0.0, dtype=np.float32)
+
+    def fake_quant_forward(self, inp, q_dict):
+        # when enable, TQT will do fakequant forward, finetune the scale
+        return TQT_Function(self.qmin, self.qmax)(inp, self.scale)
+
+    def normal_foward(self, inp, q_dict):
+        # when disable, TQT will do normal forward, initialize scale weight
+        tmp_scale = F.maximum(F.abs(q_dict["min_val"]), F.abs(q_dict["max_val"]))
+        tmp_scale = F.log(tmp_scale / 127) / F.log(2)
+        F.add_update(self.scale, tmp_scale, alpha=0.0, beta=1.0, bias=0.0)
         return inp
+
+    def get_dtype(self):
+        return get_quantized_dtype(self.dtype, 2 ** self.scale.numpy()[0], None)
+
+
+class FakeQuantize(_FakeQuantize):
+    r"""
+    A module to do quant and dequant according to observer's scale and zero_point.
+    """
+
+    def fake_quant_forward(self, inp, q_dict):
+        if q_dict["mode"] == ObserverMode.SYMMERTIC:
+            scale = q_dict["scale"]
+            # Quant
+            oup = Round()(inp / scale)
+            # clip
+            oup = F.minimum(F.maximum(oup, self.qmin), self.qmax)
+            # DeQuant
+            oup = (oup) * scale
+            return oup
+        else:
+            scale = q_dict["scale"]
+            zero_point = q_dict["zero_point"]
+            # Quant
+            oup = Round()(inp / scale) + zero_point
+            # clip
+            oup = F.minimum(F.maximum(oup, self.qmin), self.qmax)
+            # DeQuant
+            oup = (oup - zero_point) * scale
+            return oup

python_module/megengine/quantization/observer.py

@@ -107,6 +107,8 @@ class MinMaxObserver(Observer):
         min_val = F.minimum(0.0, inp_min_val)
         max_val = F.maximum(0.0, inp_max_val)
         q_dict = create_observer_dict(self.mode)
+        q_dict["min_val"] = inp_min_val
+        q_dict["max_val"] = inp_max_val
         if self.mode == ObserverMode.SYMMERTIC:
             symmetric_max_vals = F.maximum(-min_val, max_val)
             # use maximun to avoid scale too small at the begin

python_module/megengine/quantization/qconfig.py

 # MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
 #
 # Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
-#
+#'
 # Unless required by applicable law or agreed to in writing,
 # software distributed under the License is distributed on an
 # "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 from ..module import Module
-from .fake_quant import FakeQuantize
+from .fake_quant import TQT, FakeQuantize
 from .observer import (
     ExponentialMovingAverageObserver,
     HistogramObserver,
@@ -52,6 +52,12 @@ class QConfig:
         self.fake_quant = fake_quant
 
 
+tqt_quant_qconfig = QConfig(
+    weight_observer=ExponentialMovingAverageObserver,
+    act_observer=ExponentialMovingAverageObserver,
+    fake_quant=TQT,
+)
+
 # Default QAT QConfigs
 min_max_fakequant_qconfig = QConfig(
     weight_observer=MinMaxObserver,

python_module/test/unit/core/test_function.py

@@ -96,7 +96,6 @@ def test_deepcopy():
     origin = Sigmoid(0)
     new = copy.deepcopy(Sigmoid(0))
     assert new.param == origin.param
-    assert new.saved_tensors == None
 
 
 def test_save_context():

python_module/test/unit/quantization/test_TQT.py

+# -*- coding: utf-8 -*-
+# MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+#
+# Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+import numpy as np
+import pytest
+
+import megengine as mge
+import megengine._internal as mgb
+from megengine.core import tensor
+from megengine.quantization.fake_quant import TQT_Function
+from megengine.test import assertTensorClose
+
+
+class numpy_TQT_Function:
+    def __init__(self, lowerbound, upperbound):
+        super().__init__()
+        self.lowerbound = lowerbound
+        self.upperbound = upperbound
+
+    def forward(self, inp, scale):
+        t = 2 ** scale
+        # t = F.maximum(t, 1e-4)
+        inp_scaled = inp / t
+        inp_clipped = np.maximum(
+            np.minimum(inp_scaled, self.upperbound), self.lowerbound
+        )
+        inp_rounded = np.round(inp_clipped)
+        inp_flq = inp_rounded * t
+        self.saved_tensors = (inp_scaled, inp_rounded, t)
+        return inp_flq
+
+    def backward(self, grad_inp_flq):
+        (inp_scaled, inp_rounded, t) = self.saved_tensors
+        mask_clip = (inp_scaled < -0.5 + self.lowerbound) + (
+            inp_scaled > self.upperbound + 0.5
+        )  # mask for accumulating the gradients of |data_scaled|>L
+        mask_quant = np.abs(
+            mask_clip - 1
+        )  # mask for accumulating the gradients with |data_scaled|<=L
+        grad_quant = (
+            grad_inp_flq * mask_quant * (inp_rounded - inp_scaled)
+        )  # gradient within |data_scaled|<=L
+        grad_clip = (
+            grad_inp_flq * mask_clip * inp_rounded
+        )  # gradient with   | data_scaled|>L
+        grad_s = grad_clip.sum() + grad_quant.sum()
+        # dL/ds = dL/dt * t * ln(2)
+        grad_s = grad_s * t * np.log(2)
+        grad_inp = grad_inp_flq * mask_quant
+        return grad_inp, grad_s
+
+
+def test_TQT():
+    f = TQT_Function(-127, 127)
+    nf = numpy_TQT_Function(-127, 127)
+
+    def check_inp(a, b, c, a_np, b_np, c_np):
+        assertTensorClose(
+            f.forward(a, b).numpy(), nf.forward(a_np, b_np).astype("float32")
+        )
+        c1, c2 = f.backward(c)
+        c1_np, c2_np = nf.backward(c_np)
+        assertTensorClose(c1.numpy(), c1_np.astype("float32"))
+        assertTensorClose(c2.numpy(), c2_np.astype("float32"))
+
+    a = tensor()
+    b = tensor()
+    a_np = np.random.random((4, 3)).astype("float32")
+    b_np = np.random.random((1)).astype("float32")
+    a.set_value(a_np)
+    b.set_value(b_np)
+    check_inp(a, b, b, a_np, b_np, b_np)