workaround the quantization for FPN

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/163

Make quantizing FPN work, note that this is not a proper fix, which might be making pytorch picking the D2 (https://github.com/facebookresearch/d2go/commit/7992f91324aee6ae59795063a007c6837e60cdb8)'s Conv2d, and we need to revert this diff if it's supported.

Differential Revision: D33523917

fbshipit-source-id: 3d00f540a9fcb75a34125c244d86263d517a359f

d2go/modeling/meta_arch/rcnn.py

@@ -9,6 +9,7 @@ import torch.nn as nn
 from d2go.export.api import PredictorExportConfig
 from d2go.utils.qat_utils import get_qat_qconfig
 from detectron2.modeling import GeneralizedRCNN
+from detectron2.modeling.backbone.fpn import FPN
 from detectron2.modeling.postprocessing import detector_postprocess
 from detectron2.projects.point_rend import PointRendMaskHead
 from detectron2.utils.registry import Registry
@@ -113,9 +114,22 @@ def _apply_eager_mode_quant(cfg, model):
         """Wrap each quantized part of the model to insert Quant and DeQuant in-place"""
 
         # Wrap backbone and proposal_generator
-        model.backbone = wrap_quant_subclass(
-            model.backbone, n_inputs=1, n_outputs=len(model.backbone._out_features)
-        )
+        if isinstance(model.backbone, FPN):
+            # HACK: currently the quantization won't pick up D2's the Conv2d, which is
+            # used by D2's default FPN (same as FBNetV2FPN), this causes problem if we
+            # warpping entire backbone as whole. The current solution is only quantizing
+            # bottom_up and leaving other parts un-quantized. TODO (T109761730): However
+            # we need to re-visit this if using other (fbnet-based) FPN module since the
+            # new FPN module might be pikced by quantization.
+            model.backbone.bottom_up = wrap_quant_subclass(
+                model.backbone.bottom_up,
+                n_inputs=1,
+                n_outputs=len(model.backbone.bottom_up._out_features),
+            )
+        else:
+            model.backbone = wrap_quant_subclass(
+                model.backbone, n_inputs=1, n_outputs=len(model.backbone._out_features)
+            )
         model.proposal_generator.rpn_head = wrap_quant_subclass(
             model.proposal_generator.rpn_head,
             n_inputs=len(cfg.MODEL.RPN.IN_FEATURES),
@@ -175,6 +189,7 @@ def _apply_eager_mode_quant(cfg, model):
 def _fx_quant_prepare(self, cfg):
     prep_fn = prepare_qat_fx if self.training else prepare_fx
     qconfig = {"": self.qconfig}
+    assert not isinstance(self.backbone, FPN), "FPN is not supported in FX mode"
     self.backbone = prep_fn(
         self.backbone,
         qconfig,
@@ -261,6 +276,7 @@ def default_rcnn_prepare_for_quant_convert(self, cfg):
     if cfg.QUANTIZATION.EAGER_MODE:
         raise NotImplementedError()
 
+    assert not isinstance(self.backbone, FPN), "FPN is not supported in FX mode"
     self.backbone = convert_fx(
         self.backbone,
         convert_custom_config_dict={"preserved_attributes": ["size_divisibility"]},

tests/modeling/test_meta_arch_rcnn.py

@@ -41,6 +41,28 @@ class TestFBNetV3MaskRCNNFP32(RCNNBaseTestCases.TemplateTestCase):
         self._test_export(predictor_type, compare_match=compare_match)
 
 
+class TestFBNetV3MaskRCNNFPNFP32(RCNNBaseTestCases.TemplateTestCase):
+    def setup_custom_test(self):
+        super().setup_custom_test()
+        self.cfg.merge_from_file("detectron2go://mask_rcnn_fbnetv3g_fpn.yaml")
+
+    def test_inference(self):
+        self._test_inference()
+
+    @RCNNBaseTestCases.expand_parameterized_test_export(
+        [
+            ["torchscript@c2_ops", True],
+            ["torchscript", True],
+            ["torchscript_int8@c2_ops", False],
+            ["torchscript_int8", False],
+        ]
+    )
+    def test_export(self, predictor_type, compare_match):
+        if os.getenv("OSSRUN") == "1" and "@c2_ops" in predictor_type:
+            self.skipTest("Caffe2 is not available for OSS")
+        self._test_export(predictor_type, compare_match=compare_match)
+
+
 class TestFBNetV3MaskRCNNQATEager(RCNNBaseTestCases.TemplateTestCase):
     def setup_custom_test(self):
         super().setup_custom_test()