征程 6 J6E/M linear 双 int16 量化支持替代方案
作者：地平线开发者
- 2025-05-21 广东
本文字数：5791 字
阅读完需：约 19 分钟
1.背景简介
当发现使用 plugin 精度 debug 工具定位到是某个 linear 敏感时，示例如下：
op_name sensitive_type op_type L1 quant_dtype flops------------------------------------- --------------- ----------------------------- ---------------- ------------------------- ------- ------------- --------------model.layernorm.rsqrt activation <class 'horizon_plugin_pytorch.nn.qat.segment_lut.SegmentLUT'> 6.52537 qint16 0(0%)model.linear2 weight <class 'horizon_plugin_pytorch.nn.qat.linear.Linear'> 5.02445 qint8 3072000(0.00%)model.layernorm.var_mean.pre_mean activation <class 'horizon_plugin_pytorch.nn.qat.functional_modules.FloatFunctional'> 3.1683 qint16 0(0%)
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可以发现，model.linear2 weight 排在了前面，且是 int8 量化。
接下来看下 baseline_statistic.txt 与 analysis_statistic.txt，其中有 model.linear2 的 input、weight、output 的数值分布范围，示例如下：
| Op Name | Mod Name | Attr | Min | Max | Mean | Var | Shape ||---------------------------------------------------------------------------------------------------------------------------------------------------------------| torch.nn.modules.linear.Linear | model.linear2 | input | 0.0000000 | 15.4210167 | 4.0793311 | 0.2532279 | torch.Size([2, 100, 256]) || torch.nn.modules.linear.Linear | model.linear2 | weight | -41.6590347 | 31.2311363 | -0.0053362 | 0.4427260 | torch.Size([60, 256]) || torch.nn.modules.linear.Linear | model.linear2 | bias | -0.4426649 | 0.3714900 | 0.0053294 | 0.0112585 | torch.Size([60]) || torch.nn.modules.linear.Linear | model.linear2 | output | -32.0065079 | 5.7881856 | 0.4558742 | 3.8736136 | torch.Size([2, 100, 60]) |
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解决方案：使用 int16 来量化这个敏感 linear 的 weight。
如果必须要求 linear input weight output 都是 int16 量化，怎么办呢？
2.知识基础
在 征程 6E/M 上，地平线 BPU 对 linear 支持的情况如下：
本文发布时是这样的
可以看到：input 和 weight 不能同时为 int16。
3.Linear input weight both int16
对于 linear input 和 weight 均需要 int16 量化的情况，可使用 broadcast mul sum 来替代验证，无需重训 float。
异同简介：broadcast_mul_sum_replace_linear 在 float 层面可以等价替换 linear，但在量化方式上存在区别：Linear weight 是 per channel 量化，weight 作为 mul 输入时，是 per tensor 量化。一般情况下：weight int8 perchannel 变成 per tensor int16，精度是正向优化。
替换方案：在 float 训练完成后替换，然后进行 calib+qat。
class SmallModel(nn.Module): def __init__(self, linear2_weight, linear2_bias): super(SmallModel, self).__init__() # 第一个 Linear: 输入 [2, 100, 256] -> 输出 [2, 100, 256] self.linear1 = nn.Linear(256, 256) self.layernorm = nn.LayerNorm(256) # 对最后一维进行归一化 self.relu = nn.ReLU() # 第二个 Linear: 输入 [2, 100, 256] -> 输出 [2, 100, 60] # self.linear2 = nn.Linear(256, 60) self.linear2_weight = linear2_weight self.linear2_bias = linear2_bias # 第三个 Linear: 输入 [2, 100, 60] -> 输出 [2, 100, 60] self.linear3 = nn.Linear(60, 60) self.quant = QuantStub() self.dequant = DeQuantStub() self.quant_linear2_weight = QuantStub() self.quant_linear2_bias = QuantStub() def forward(self, x): x = self.quant(x) linear2_weight = self.quant_linear2_weight(self.linear2_weight) linear2_bias = self.quant_linear2_bias(self.linear2_bias) # 第一个 Linear x = self.linear1(x) # [2, 100, 256] x = self.layernorm(x) # [2, 100, 256] x = self.relu(x) # [2, 100, 256] # 第二个 Linear # x = self.linear2(x) # [2, 100, 60] # =================================== # 使用 broadcast mul + sum 替换linear # =================================== # 广播乘法：输入 [2, 100, 256] 与权重 [60, 256] 进行广播 broadcast_mul = x.reshape(2, 100, 1, 256) * linear2_weight.reshape(1, 1, 60, 256) # [2, 100, 60, 256] # 按最后一个维度求和：sum 操作模拟线性层的加权求和 sum_output = broadcast_mul.sum(dim=-1) # [2, 100, 60] # 加上偏置 x = sum_output + linear2_bias # [2, 100, 60] # 第三个 Linear x = self.linear3(x) x = self.dequant(x) return x
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broadcast mul sum 替换方案，均支持 int16。
注意事项：如果 mul 的输出 绝大多数 数值都在 0 附近 -> MSE 校准受异常值影响较大 -> 输出 scale 非常大 -> 0 附近的大量小数值被舍入成 0 -> sum 和发生巨大偏差。
影响范围：mul 后面跟着 sigmoid 或 add+sigmoid 时影响很大。
解决方案：mul 输出设置 fixed scale 为 7/32767，因为 sigmoid 并不需要太大的输入，而 mul 的输出分布需要小 scale。
4.全流程示例
从表中可以看到，在 linear 需要 int16 量化的场景，input/output int16 对应的 latency 最短，其次是 weight output int16 input int8，最差的是三者都需要 int16，针对这三种情况，下面分别提供完整的例子供参考。
信息描述
注意：非完全等价，仅作为参考
4.1 示例代码
import torchfrom horizon_plugin_pytorch import set_march, Marchset_march(March.NASH_M)from horizon_plugin_pytorch.quantization import prepare, set_fake_quantize, FakeQuantStatefrom horizon_plugin_pytorch.quantization import QuantStubfrom horizon_plugin_pytorch.quantization.hbdk4 import exportfrom horizon_plugin_pytorch.quantization.qconfig_template import calibration_8bit_weight_16bit_act_qconfig_setter, ModuleNameQconfigSetterfrom horizon_plugin_pytorch.quantization.qconfig import get_qconfig, MSEObserver, MinMaxObserverfrom horizon_plugin_pytorch.dtype import qint8, qint16from torch.quantization import DeQuantStubimport torch.nn as nnfrom horizon_plugin_pytorch.quantization import hbdk4 as hb4from hbdk4.compiler import convert, save, hbm_perf, visualize, compile
import torchimport torch.nn as nn
# 定义网络结构class SmallModel(nn.Module): def __init__(self, linear2_weight, linear2_bias): super(SmallModel, self).__init__() # 第一个 Linear: 输入 [2, 100, 256] -> 输出 [2, 100, 256] self.linear1 = nn.Linear(256, 256) self.layernorm = nn.LayerNorm(256) # 对最后一维进行归一化 self.relu = nn.ReLU() # 第二个 Linear: 输入 [2, 100, 256] -> 输出 [2, 100, 60] # self.linear2 = nn.Linear(256, 60) self.linear2_weight = linear2_weight self.linear2_bias = linear2_bias # 第三个 Linear: 输入 [2, 100, 60] -> 输出 [2, 100, 60] self.linear3 = nn.Linear(60, 60) self.quant = QuantStub() self.dequant = DeQuantStub() self.quant_linear2_weight = QuantStub() self.quant_linear2_bias = QuantStub() def forward(self, x): x = self.quant(x) linear2_weight = self.quant_linear2_weight(self.linear2_weight) linear2_bias = self.quant_linear2_bias(self.linear2_bias) # 第一个 Linear x = self.linear1(x) # [2, 100, 256] x = self.layernorm(x) # [2, 100, 256] x = self.relu(x) # [2, 100, 256] # 第二个 Linear # x = self.linear2(x) # [2, 100, 60] # =================================== # 使用 broadcast mul + sum 替换linear # =================================== # 广播乘法：输入 [2, 100, 256] 与权重 [60, 256] 进行广播 broadcast_mul = x.reshape(2, 100, 1, 256) * linear2_weight.reshape(1, 1, 60, 256) # [2, 100, 60, 256] # 按最后一个维度求和：sum 操作模拟线性层的加权求和 sum_output = broadcast_mul.sum(dim=-1) # [2, 100, 60] # 加上偏置 x = sum_output + linear2_bias # [2, 100, 60] # 第三个 Linear x = self.linear3(x) x = self.dequant(x) return x
float_ckpt_path = "model_path/float-checkpoint.ckpt" float_state_dict = torch.load(float_ckpt_path)# 遍历 OrderedDict，查找包含 "linear2" 的键for key, value in float_state_dict.items(): # if "linear2" in key: # print(f"Key: {key}, Value: {value.shape}") if key == "linear2.weight": linear2_weight = value if key == "linear2.bias": linear2_bias = value
# example_input = torch.randn(2, 100, 256)file_path = "random_data.pt"example_input = torch.load(file_path)model = SmallModel(linear2_weight, linear2_bias)missing_keys, unexpected_keys = model.load_state_dict(float_state_dict, strict=False)print("missing_keys & unexpected_keys:", missing_keys, '\n', unexpected_keys)
# 前向传播output = model(example_input)print("float输出数据:", output)torch.save(output, "model_path/6_model_float_output.pt")print("输入形状:", example_input.shape)print("输出形状:", output.shape)
# A global march indicating the target hardware version must be setted before prepare qat.set_march(March.NASH_M)
calib_model = prepare(model.eval(), example_input, qconfig_setter=( calibration_8bit_weight_16bit_act_qconfig_setter, ), )
calib_model.eval()set_fake_quantize(calib_model, FakeQuantState.CALIBRATION)calib_model(example_input)
calib_model.eval() set_fake_quantize(calib_model, FakeQuantState.VALIDATION)calib_out = calib_model(example_input)print("calib输出数据:", calib_out)qat_bc = export(calib_model, example_input)hb_quantized_model = convert(qat_bc, March.NASH_M)
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4.2 比较替代方案的输出一致性
linear2 weight input output int16
float输出数据: tensor([[[-0.3016, 0.1338, -0.5251, ..., -0.0551, -0.2093, -0.0308], [-0.1969, -0.0131, -0.3287, ..., 0.3234, -0.0869, -0.0637], [-0.3056, 0.1478, -0.2673, ..., 0.2355, -0.3487, 0.0134], ..., [-0.3990, -0.0389, -0.1686, ..., -0.0046, -0.4131, 0.0482], [-0.1059, 0.2431, -0.1886, ..., 0.0787, -0.3454, 0.0231], [-0.2134, -0.1071, -0.0575, ..., 0.3434, -0.1661, 0.2248]]], grad_fn=<ViewBackward0>) calib输出数据: tensor([[[-0.3038, 0.1370, -0.5269, ..., -0.0571, -0.2111, -0.0296], [-0.1975, -0.0111, -0.3280, ..., 0.3215, -0.0884, -0.0637], [-0.3052, 0.1488, -0.2677, ..., 0.2348, -0.3479, 0.0132], ..., [-0.3988, -0.0393, -0.1662, ..., -0.0055, -0.4117, 0.0484], [-0.1058, 0.2442, -0.1890, ..., 0.0780, -0.3447, 0.0240], [-0.2142, -0.1061, -0.0587, ..., 0.3422, -0.1657, 0.2255]]], grad_fn=<ViewBackward0>)
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broadcast mul sum int16
float输出数据: tensor([[[-0.3016, 0.1338, -0.5251, ..., -0.0551, -0.2093, -0.0308], [-0.1969, -0.0131, -0.3287, ..., 0.3234, -0.0869, -0.0637], [-0.3056, 0.1478, -0.2673, ..., 0.2355, -0.3487, 0.0134], ..., [-0.3990, -0.0389, -0.1686, ..., -0.0046, -0.4131, 0.0482], [-0.1059, 0.2431, -0.1886, ..., 0.0787, -0.3454, 0.0231], [-0.2134, -0.1071, -0.0575, ..., 0.3434, -0.1661, 0.2248]]], grad_fn=<ViewBackward0>)calib输出数据: tensor([[[-0.3038, 0.1370, -0.5269, ..., -0.0571, -0.2111, -0.0296], [-0.1975, -0.0111, -0.3280, ..., 0.3215, -0.0884, -0.0637], [-0.3051, 0.1487, -0.2678, ..., 0.2349, -0.3478, 0.0132], ..., [-0.3988, -0.0392, -0.1662, ..., -0.0055, -0.4117, 0.0484], [-0.1058, 0.2442, -0.1890, ..., 0.0780, -0.3447, 0.0240], [-0.2142, -0.1061, -0.0586, ..., 0.3423, -0.1657, 0.2255]]], grad_fn=<ViewBackward0>)
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