Reduce memory usage for symmetric choose_qparams

test/quantization/test_quant_primitives.py

@@ -240,6 +240,16 @@ def test_choose_qparams_tensor_asym_eps(self):
         eps = torch.finfo(torch.float32).eps
         self.assertEqual(scale, eps)
 
+    @unittest.skipIf(not torch.cuda.is_available(), "skipping when cuda is not available")
+    def test_get_group_qparams_symmetric_memory(self):
+        """Check the memory usage of the op"""
+        weight = torch.randn(1024, 1024).to(device="cuda")
+        original_mem_use = torch.cuda.memory_allocated()
+        n_bit = 4
+        groupsize = 128
+        (scale_ao, _) = get_group_qparams_symmetric(weight, n_bit, groupsize)
+        after_choose_qparams_mem_use = torch.cuda.memory_allocated()
+        self.assertTrue(after_choose_qparams_mem_use < 1.2 * original_mem_use)
 
 if __name__ == "__main__":
     unittest.main()

torchao/quantization/quant_primitives.py

@@ -260,6 +260,8 @@ def choose_qparams_affine(
         Tuple of scales and zero_points Tensor with requested dtype
     """
     quant_min, quant_max = _get_and_check_qmin_qmax(target_dtype, quant_min, quant_max)
+    assert mapping_type in [MappingType.SYMMETRIC, MappingType.ASYMMETRIC], f"Unsupported mapping type: {mapping_type}"
+
     if scale_dtype is None:
         scale_dtype = input.dtype
     if zero_point_dtype is None:
@@ -269,23 +271,20 @@ def choose_qparams_affine(
     shape_for_reduction, reduction_dims = _get_reduction_params(block_size, input.size())
     input = input.view(shape_for_reduction)
 
-    if mapping_type == MappingType.SYMMETRIC:
-        amax = torch.amax(torch.abs(input), dim=reduction_dims, keepdim=False)
-        scale = amax / (float(quant_max - quant_min) / 2)
-        zero_point = torch.ones_like(scale)
-        zero_point *= int((quant_min + quant_max + 1) / 2)
-    elif mapping_type == MappingType.ASYMMETRIC:
-        min_val = torch.amin(input, dim=reduction_dims, keepdim=False)
-        max_val = torch.amax(input, dim=reduction_dims, keepdim=False)
+    min_val = torch.amin(input, dim=reduction_dims, keepdim=False)
+    max_val = torch.amax(input, dim=reduction_dims, keepdim=False)
 
-        min_val_neg = torch.min(min_val, torch.zeros_like(min_val))
-        max_val_pos = torch.max(max_val, torch.zeros_like(max_val))
+    min_val_neg = torch.min(min_val, torch.zeros_like(min_val))
+    max_val_pos = torch.max(max_val, torch.zeros_like(max_val))
 
+    if mapping_type == MappingType.SYMMETRIC:
+        max_val_pos = torch.max(-min_val_neg, max_val_pos)
+        scale = max_val_pos / (float(quant_max - quant_min) / 2)
+        zero_point = torch.full_like(scale, int((quant_min + quant_max + 1) / 2))
+    else:
         scale = (max_val_pos - min_val_neg) / float(quant_max - quant_min)
         zero_point = quant_min - torch.round(min_val_neg / scale)
         zero_point = torch.clamp(zero_point, quant_min, quant_max)
-    else:
-        raise RuntimeError(f"Unsupported mapping type: {mapping_type}")
 
     if eps is None:
         eps = torch.finfo(input.dtype).eps