New ML Networks Far Outperform Old Standbys

By Quadric

March 25, 2024

The ResNet family of machine learning algorithms, introduced to the AI world in 2015, pushed AI forward in new ways. However, today’s leading edge classifier networks – such as the Vision Transformer (ViT) family - have Top 1 accuracies a full 10% points of accuracy ahead of the top-rated ResNet in the leaderboard. ResNet is old news. Surely other new algorithms will be introduced in the coming years.

Let’s take a look back at how far we’ve come. Shortly after introduction, new variations were rapidly discovered that pushed the accuracy of ResNets close to the 80% threshold (78.57% Top 1 accuracy for ResNet-152 on ImageNet). This state-of-the-art performance at the time coupled with the rather simple operator structure that was readily amenable to hardware acceleration in SoC designs turned ResNet into the go-to litmus test of ML inference performance. Scores of design teams built ML accelerators in the 2018-2022 time period with ResNet in mind.

These accelerators – called NPUs – shared one common trait – the use of integer arithmetic instead of floating-point math. Integer formats are preferred for on-device inference because an INT8 multiply-accumulate (the basic building block of ML inference) can be 8X to 10X more energy efficient than executing the same calculation in full 32-bit floating point. The process of converting a model’s weights from floating point to integer representation is known as quantization. Unfortunately, some degree of fidelity is always lost in the quantization process.

NPU designers have, in the past half-decade, spent enormous amounts of time and energy fine-tuning their weight quantization strategies to minimize the accuracy loss of an integer version of ResNet compared to the original Float-32 source (often referred to as Top-1 Loss). For most builders and buyers of NPU accelerators, a loss of 1% or less is the litmus test of goodness. Some even continue to fixate on that number today, even in the face of dramatic evidence that suggests now-ancient networks like ResNet should be relegated to the dustbin of history. What evidence, you ask?

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