Optimization
Large Language Model Graph Customization with OpenVINO™ Transformations API
Authors: Xiake Sun, Wenyi Zou, Fiona Zhao
Introduction
A Large Language Model (LLM) is a type of artificial intelligence algorithm that uses deep learning techniques and massively large data sets to understand, summarize, generate and predict new content.
OpenVINO™ optimizes the deployment of LLMs, enhancing their performance and integration into various applications. We already provide general guide to use LLMs with OpenVINO™, from model loading and conversion to advanced use cases.
In this blog, we will introduce some useful method to customize Large Language model’s graph with OpenVINO™ transformation API.
OpenVINO™ Runtime has three main transformation types:
- Modelpass: straightforward way to work with ov::Model directly
- Matcherpass: pattern-based transformation approach
- Graphrewrite pass: container for matcher passes needed for efficient execution.
In this blog, we mainly use ov::pass::MatcherPassto customize model subgraph via pattern-based transformation.
Here are common steps to implement graph customization using ov::pass::MatcherPass.
- Create a pattern
- Implement a callback
- Register the pattern and Matcher
- Execute MatcherPass
In this blog, we will use an open-source LLMs Qwen1.5-7B-Chat-GPTQ-Int4 from Alibaba Cloud with guide for model conversion and graph customization methods.
Qwen Pytorch to OpenVINO™ Model conversion
Here we can use openvino.genai repo to convert Qwen1.5 GPTQ INT4 Pytroch model to OpenVINO™model.
Converted model can be find in path “Qwen1.5-7B-Chat-GPTQ-Int4-OV/pytorch/dldt/GPTQ_INT4-FP16/".
Insert custom layer to OpenVINO™ model
Vocabularysize in the context of LLMs refers to the total number of unique words, or tokens, that the model can recognize and use. The larger the vocabulary size,the more nuanced and detailed the model’s understanding of language can be,however, it also requires more computational and memory resources for deployment. E.g. Qwen’s vocabulary size(151936) is almost 5x that Llama2 (32000), therefore additional optimization is required for efficient deployment.
We found that the following pattern existed in the Qwen model in Figure 2:
To compute the first token generation for the input prompt with shape [1, seq_length], we need to calculate a MatMul operation based on two inputs.
- First input is a reshape node output with shape[1, seq_length, 4096]
- Second input is a constant value that contains the model’s vocabulary with shape [4096,151936]
Then Matmul calculates two inputs [1, seq_length, 4096] * [4096,151936] to output large logits [1, seq_length,151936]. However, for the next token prediction, we only need the last element [1,4096] in 1st dimension from logits for sampling.
The main idea is to insert a slice operation between Reshape and Matmul nodes to extract only the last element in 2nd dimension of reshape node output as the first input with shape [1,4096] for computation. Therefore, Matmul computation can be reduced from [1, seq_len, 4096] * [1, 4096, 151936] = [1, seq_len, 151936] to [1, 1, 4096] *[4096, 151936] = [1, 1, 151936], which can reduce first token latency and memory consumption.
Here is a sample code to implement the workflow defined in Figure2 to reduce Qwen's last Matmul computation and memory usage:
We defined a OpenVINO™ transformation "InsertSlice" to find the logits (Results) node via ov::pass::MatchPass, then search along root->parent->grandparent node to find the Reshape node. Afterward, we insert a Slice node between the Reshape and Matmul nodes to extract the last element of seq_length with shape [1,1,4096]. In the end, we apply "InsertSlice" transformation to original OpenVINO™ model and save modified model on disk for deployment.
Modify model weights of specified layer in OpenVINO™ model
In case you want to update certain model layer weights after model training or fine-tuning/compression.
E.g. if you have an INT4 weight-compressed model using another model compression method, e.g. AWQ, you may want to transfer model weights optimized with the quantization method.
The most general method will be to convert the original model to OpenVINO™ model if the model direct conversion works. However, if first option is not works out of box, an alternative option is to replace the model weights from OpenVINO™ models with external fine-tuning model weights.
Here we introduce a common method to modify layer weights of Qwen model via OpenVINO™ transformation API.
As Figure 3 shows, the goal is to replace model weights and scale of the original Constant node with external fine-tuned weights and scale data.
At first, we use ov::pass::MatchPass method to find the Convert node after the target node. Then we create a new constant node with external weight saved as a numpy array. Please note, GPTQ int4 model weight is saved asuint4 (U4) binary format, while numpy can only represent data with numpy.uint8. Therefore, we use a help function to pack 2 uint4 binary data as 1 uint8 binary data. Then we replace the Convert input port from the original Constant node to the new Constant node. Since the old constant node has no consumers and is neither the Result nor the Sink operation whose shared pointer counter is zero, the operation will be destructed and not be accessible anymore.
Here is a sample code to implement the workflow defined in Figure3 to replace Qwen Constant node via the new Constant node with external data:
We defined a OpenVINO™ transformation "InsertWeights" to find the target constant node via ov::pass::MatchPass, then we create a new Constat node with external numpy data and pack it as uint4 OpenVINO™ Tensor to replace original constant node in graph. In the end, we apply "InsertWeights" transformation to original OpenVINO™ model and save modified model on disk for deployment.
Conclusion
In this blog, we introduce how to apply graph customization based on OpenVINO™ model with OpenVINO™ transformation API. Furthermore, we show two examples of inserting layers & modifying layer weights based on Qwen LLM model with simple Python code.
Reference
IntegrateOpenVINO™ with Your Application – Model Representation
Q4'23: Technology Update – Low Precision and Model Optimization
Authors
Alexander Kozlov, Nikita Savelyev, Nikolay Lyalyushkin, Vui Seng Chua, Pablo Munoz, Alexander Suslov, Andrey Anufriev, Liubov Talamanova, Yury Gorbachev, Nilesh Jain, Maxim Proshin
Summary
This quarter we observe that most of the work is still dedicated to the Large Language Model optimization. Researchers try to break through W4A8 quantization setup for LLMs achieving the accuracy results that allows considering such optimized models for deployment scenario. Some teams work on lower-precision settings such as 2-bit weight quantization or even binary weight compression. Interestingly, some teams propose to stick to a higher bit-width (FP6) and data-free optimization approach to avoid overfitting to calibration data. We also see an increasing interest in applying various types of weight sparsity in LLMs. And, of course, we should note the tremendous improvement in the inference time of Diffusion models caused by the decrease in the overall number of iterations in the diffusion process. This allows running variations of Stable Diffusion on mobile devices in the below 1 second.
Papers with notable results
Quantization
- AWEQ: Post-Training Quantization with Activation-Weight Equalization for Large Language Models by Jilin University (https://arxiv.org/pdf/2311.01305.pdf). Authors apply a known recipe for DL models quantization to LLM models. It contains weight equalization and bias correction methods stacked together. The difference is in how they estimate parameters and where to apply both methods. The method shows good results for W8A8 and W4A8 settings and outperforms GPTQ method on LLAMA and OPT models.
- AFPQ: Asymmetric Floating Point Quantization for LLMs by China Universities and Microsoft Research Asia (https://arxiv.org/pdf/2311.01792.pdf).Authors propose accurate asymmetric schema for the floating-point quantization. Instead of using typical asymmetric schema with scale and zero point, they use just2 scales: one is for positive values and another - for negative ones. It gives better accuracy NF4/NF3 quantization on different LLAMA models with no memory overhead. Code is available: https://github.com/zhangsichengsjtu/AFPQ.
- Enhancing Computation Efficiency in Large Language Models through Weight and Activation Quantization by Hanyang University, SAPEON Korea Inc., Seoul National University (https://arxiv.org/pdf/2311.05161.pdf). Authors present two techniques: activation-quantization-aware scaling (a trade-off between SQ and AWQ) and sequence-length-aware calibration (adaptation of OPTQ to various sequence lengths) to enhance PTQ by considering the combined effects on weights and activations and aligning calibration sequence lengths to target tasks. They also introduce dINT, a hybrid data format combining integer and denormal representations, to address the underflow issue in W4A8 quantization, where small values are rounded to zero. The combined approach allows for achieving superior results compared to baselines. However, dINT has a limitation of efficient implementation on a general-purpose HW, such as CPU and GPU.
- POST-TRAINING QUANTIZATIONWITH LOW-PRECISION MINIFLOATS AND INTEGERS ON FPGAS by AMD Research, National University of Singapore, and Tampere University (https://arxiv.org/pdf/2311.12359.pdf). Authors compare integer and mini float quantization techniques, encompassing a combination of state-of-the-art PTQ methods, such as weight equalization, bias correction, SmoothQuant, learned rounding, and GPTQ. They explore the accuracy-hardware tradeoffs, providing analysis for three models -ResNet-18, MobileNetV2, and ViT-B32 - based on a custom FPGA implementation. Experiments indicate that mini float quantization typically outperforms integer quantization for bit-widths of four or more, both for weights and activations. However, when compared against FPGA hardware cost model, integer quantization often retains its Pareto optimality due to its smaller hardware footprint at a given precision.
- I&S-ViT: An Inclusive& Stable Method for Pushing the Limit of Post-Training ViTs Quantization by Xiamen University, Tencent, and Peng Cheng Laboratory (https://arxiv.org/pdf/2311.10126.pdf). The paper introduces a method that regulates the PTQ of ViTs in an inclusive and stable fashion. It first identifies two issues in the PTQ of ViTs: (1)Quantization inefficiency in the prevalent log2 quantizer for post-Softmax activations; (2) Rugged and magnified loss landscape in coarse-grained quantization granularity for post-LayerNorm activations. Then, the method addresses these issues by introducing: (1) A novel shift-uniform-log2 quantizer(SULQ) that incorporates a shift mechanism followed by uniform quantization to achieve both an inclusive domain representation and accurate distribution approximation; (2) A three-stage smooth optimization strategy that amalgamates the strengths of channel-wise and layer-wise quantization to enable stable learning. The method achieves comparable results in the W4A4 and W3A3 quantization settings.
- Quantizable Transformers: Removing Outliers by Helping Attention Heads Do Nothing by Qualcomm AI Research (https://arxiv.org/pdf/2306.12929.pdf). This work aims to remove outliers by construction (pretraining) so that transformer can be quantized easily without the need of finer quantization granularity (e.g. per channel, per group). The authors root-caused that outliers in trained transformers are essentially the artifact of attention head attenuating uninformative tokens and outliers emerged in the formulation/backpropagation of softmax, residual connections and layer normalization to sustain the effect of these tokens. Two independent solutions are proposed - (1) Clipped softmax that allows exact zeros and ones in softmax to avoid growing outliers during training. (2) Gated attention which is a tiny neural network (linear+sigmoid) added to the vanilla attention to decouple the needs of large attention output for disregarding the uninformative tokens. Pretraining with the proposed formulation on BERT, OPT and ViT has been shown to converge similarly if not better than baseline recipe. Most notably, the ease of per-tensor int8 static quantization to both weight and activation in post-training fashion has been empirically verified. Code is coming soon at https://github.com/qualcomm-ai-research/outlier-free-transformers
- A Speed Odyssey for Deployable Quantization of LLMs by Meituan (https://arxiv.org/pdf/2311.09550.pdf).Authors propose a solution for deployable W4A8 quantization that comprises a tailored quantization configuration and a novel Fast GEMM kernel for 4-bitinteger matrix multiplication that reduces the cost, and it achieves 2.23× and1.45× speed boosting over the TensorRT-LLM FP16 and INT8 implementation respectively. The W4A8 recipe is proven mostly on par with the state-of-the-art W8A8 quantization method SmoothQuant on a variety of common language benchmarks for the state-of-the-art LLMs.
- TFMQ-DM: Temporal Feature Maintenance Quantization for Diffusion Models by SenseTime and universities of US, China and Australia (https://arxiv.org/pdf/2311.16503.pdf). Authors investigate the problems in quantization of diffusion models and claim that these models heavily depend on the time-step t to achieve satisfactory multi-round denoising when t is encoded to a temporal feature by a few modules totally irrespective of the sampling data. They propose a Temporal Feature Maintenance Quantization framework building upon a Temporal Information Block which is just related to the time-step t and unrelated to the sampling data. Powered by this block design, authors propose temporal information aware reconstruction and finite set calibration to align the full-precision temporal features in a limited time. The method achieves accurate results even in W4A8quantization setting.
- QUIK: TOWARDS END-TO-END4-BIT INFERENCE ON GENERATIVE LARGE LANGUAGE MODELS by ETH Zurich, Institute of Science and Technology Austria, Xidian University, KAUST, Neural Magic (https://arxiv.org/pdf/2310.09259v2.pdf). The paper addresses the problem where both weights and activations should be quantized. Authors show that the majority of inference computations for large generative models such as LLaMA, OPT, and Falcon can be performed with both weights and activations being cast to 4 bits, in a way that leads to practical speedups, while at the same time maintaining good accuracy. They achieve this via a hybrid quantization strategy called QUIK, which compresses most of the weights and activations to 4-bit, while keeping some outlier weights and activations in higher precision which leads to practical end-to-end throughput improvements of up to 3.4x relative to FP16 execution. Code is available at: https://github.com/IST-DASLab/QUIK.
- Post-training Quantization with Progressive Calibration and Activation Relaxing for Text-to-Image Diffusion Models by Tsinghua University (https://arxiv.org/pdf/2311.06322.pdf). Authors propose a post-training quantization method for text-to-image diffusion models, which consists of a progressive calibration strategy that considers the accumulated quantization error across timesteps, and an activation relaxing strategy that improves the performance with a small cost. They also propose a new QDiffBench benchmark, which utilizes data in the same domain for a more accurate evaluation of the generation accuracy.
- Enabling Fast 2-bit LLM on GPUs: Memory Alignment, Sparse Outlier, and Asynchronous Dequantization by Shanghai Jiao Tong University and Tsinghua University (https://arxiv.org/pdf/2311.16442.pdf).The paper proposes range-aware quantization with memory alignment. It points out that the range of weights by groups varies. Thus, only 25% of the weights are quantized using 4-bit with memory alignment. Such a method reduces the accuracy loss for 2-bit Llama2-7b quantization from 8.7% to 2.9%. Authors show as well that only a small fraction of outliers exist in weights quantized using2-bit. These quantize these sparse outliers with < 3% increased average weight bit and improve the accuracy by >0.5%. They also accelerate GPU kernels by introducing asynchronous dequantization achieving 3.92× improvement on a kernel level.
- ZeroQuant(4+2): Redefining LLMs Quantization with a New FP6-Centric Strategy for Diverse Generative Tasks by DeepSpeed (https://arxiv.org/pdf/2312.08583.pdf).Authors show that popular data-aware LLM compression methods such as GPTQ can overfit to calibrated datasets especially on moderate-size LLMs (<=1B). They also illustrate that FP6, employing a basic round-to-nearest (RTN) algorithm and a per-channel quantization approach, consistently achieves accuracy on par with full-precision models. They propose an unpacking (mapping) scheme for FP8 so that it can be efficiently used with FP16 inference.
Pruning/Sparsity
- Sparse Fine-tuning for Inference Acceleration of Large Language Models by IST Austria, Skoltech & Yandex, and Neural Magic (https://arxiv.org/pdf/2310.06927.pdf). The paper analyses the challenges of LLMs pruning, namely loss spikes leading to divergence, poor recovery from fine-tuning, and overfitting. To overcome these issues, authors incorporate standard cross-entropy, output knowledge distillation, and a type of per-token ℓ2 knowledge distillation on top of SparseGPT method. They show that the resulting sparse models can be executed with inference speedups on CPU and GPU, especially when stacking with INT8quantization. The code is available: https://github.com/IST-DASLab/SparseFinetuning.
- ReLU Strikes Back: Exploiting Activation Sparsity in LLMs by Apple. (https://arxiv.org/pdf/2310.04564.pdf). This work advocates to reinstate ReLU as main activation function in LLMs due to its intriguing property – high post-ReLU activation sparsity can be translated to computational efficiency with sparse runtime. To overcome training from scratch and for LLMs employing GeLU/SiLU, the paper proposes “Relufication”, a two-stage uptraining by first replacing non-ReLU activations in pre-trained LLMs with ReLU, and then appending ReLU to normalization layers in second stage for more sparsity. With increase of activation sparsity, the authors also observe high overlapping activated neurons during decoding (termed aggregated sparsity) and suggest weight reuse to alleviate memory transfer. The authors show application of aggregated sparsity in speculative decoding and demonstrate 27% speedup of OPT-6.7B at a minor degradation of perplexity.
- Deja Vu: Contextual Sparsity for Efficient LLMs at Inference Time by Rice University, Zhe Jiang University, Stanford University, University of California, ETH Zurich, Adobe Research, MetaAI, Carnegie Mellon University (https://proceedings.mlr.press/v202/liu23am/liu23am.pdf). Authors propose a contextual dynamic sparsity method for LLMs. Contrary to a usual sparsity approach where a model is pruned once and then inferenced on every input sample in the same pruned state, here authors compute the set of pruned operations on the run resulting in a more flexible pruning scheme. Foreach transformer layer this is achieved by predicting set of MHA heads and MLP matrix columns to exclude based on previous layers activations. Prediction is performed by small separately trained perceptron networks. To remove the performance bottleneck produced by the need to inference of perceptron networks authors propose to make sparsity predictions for (i+1)-th transformer layer based on activations from (i-1)-th layer, resulting in parallel computation of i-th layer and sparsity sets for (i+1)-th layer. This is viable due to shown similarity between activations of neighboring layers in LLMs. For OPT-175Bmodel the approach achieves over 6x performance improvement compared to Hugging Face implementation and over 2x improvement compared to state-of-the-art FasterTransformer model.
- SparseByteNN: A Novel Mobile Inference Acceleration Framework Based on Fine-Grained Group Sparsity by ByteDance (https://arxiv.org/pdf/2310.19509.pdf). The paper introduces SparseByteNN, consisting of three components: a)compression algorithm component, which provides out-of-the-box pruning capabilities for pre-trained models b) model conversion tool, which converts the model IR of the training framework into Model IR of sparse engine c) sparse inference engine, which provides efficient inference implementation compatible with CPUs for fine-grained kernel group sparsity. Experimental results on Qualcomm 855 show that for 30% sparse MobileNet-v1, SparseByteNN achieves 1.27×speedup over the dense version. The code will be available at: https://github.com/lswzjuer/SparseByteNN.
Neural Architecture Search
- LoNAS: Elastic Low-Rank Adapters for Efficient Large Language Models by Anonymous (https://openreview.net/pdf?id=pzB-1OCS6gd). Researchers demonstrate a novel integration of low-rank (LoRA)adapters with Neural Architecture Search. LoNAS efficiently fine-tunes and compress large language models (LLMs). A weight-sharing super-network is generated using the frozen weights of the input model, and the attached elastic low-rank adapters. The reduction in trainable parameters results in less the memory requirements to train the super-network, enabling the manipulation of LLMs in resource-constrained devices, without sacrificing the performance of the resulting compressed models. LoNAS’ high-performing compressed models result in faster inference times, cost savings during the model’s lifetime, and an increase in the range of devices in which large language models can be deployed. Experiments’ results on six reasoning datasets demonstrate the benefits of LoNAS.
- Bridging the Gap between Foundation Models and Heterogenous Federated Learning by Iowa State U. and Intel Labs (https://arxiv.org/abs/2310.00247). This paper explores the application of Neural Architecture Search (NAS) in combination with Federated Learning (FL). The proposed framework, Resource-aware Federated Foundation Models (RaFFM) introduces model compression and salient parameter prioritization in the context of Federated Learning, allowing for the collaborative training of large foundation models using heterogeneous devices. Compared to traditional FL methods, RaFFM yields better resource utilization, without sacrificing in model performance.
- Rankitect: Ranking Architecture Search Battling World-class Engineers at Meta Scale by Meta Platforms (https://arxiv.org/pdf/2311.08430.pdf). Researchers at Meta demonstrate the real-world applications of Neural Architecture Search (NAS). They apply NAS to production models, e.g., Click Through Rate (CTR) model, on a system that serves billions of users. The baseline models explored in this work have already been optimized by world-class engineers. The proposed NAS framework, Rankitect, improves over existing models by exploring search spaces with no inductive bias from the baseline models, and discovers new models from scratch that outperform those hand-crafted by human experts. Rankitect also keeps human engineers in-the-loop by allowing the manual design of search spaces, which results in even more efficient models.
- QuadraNet: Improving High-Order Neural Interaction Efficiency with Hardware-Aware Quadratic Neural Networks by George Mason University, University of Maryland, University at Buffalo, Peking University (https://arxiv.org/pdf/2311.17956.pdf). This paper presents QuadraNet, a new neural network design methodology based on efficient quadratic neurons that captures high-order neural interactions similar to Transformer-based models. The design of this alternative to Transformer-based models is hardware-aware through the application of Neural Architecture Search(NAS). Experiments with QuadraNets show improvements of 1.5x in throughput without any reduction in accuracy compared to their Transformer-based counterparts.
Other
- Divergent Token Metrics: Measuring degradation to prune away LLM components – and optimize quantization by Aleph Alpha, Hessian.AI and German Universities. (https://arxiv.org/pdf/2311.01544.pdf). The work highlights that the commonly used perplexity (PPL) metric in compression research does not reflect the degradation of compressed model and cannot distinguish subtleties (see figure below). The authors propose a family of divergent token metrics (DTM), namely First Token Divergence, i.e., when the first diverging token happens w.r.t baseline generated text, as well as Share of Divergent Tokens denoting the total number of divergent tokens. In a series of experiments pertaining to layer-wise quantization or pruning, DTM-based ranking consistently outperforms PPL-based ranking methods.
- SIMPLIFYING TRANSFORMERBLOCKS by ETH Zurich (https://arxiv.org/pdf/2311.01906.pdf). The paper introduces a set of Transformer block pruning techniques that makes them more lightweight from the number of parameters and computations standpoint. This set includes: removing skip connection both in the Attention sub-block and Feed-Forward sub-block, removing value and projection parameters, removing normalization layers, and model depth scaling. Authors also show how to recover the accuracy after model perturbation using fine-tuning. The proposed method produces the decoder and decoder Transformer models that perform on part with their baselines: 15% faster training throughput, and using 15% fewer parameters.
- MobileDiffusion: Subsecond Text-to-Image Generation on Mobile Devices by Google (https://arxiv.org/pdf/2311.16567.pdf).The paper presents a comprehensive guide for crafting highly efficient text-to-image diffusion models. Authors applied the following tricks to highly optimize UNet model in the Diffusion pipeline: more transformers in the middle of Unet (at lower resolution), retaining cross-attention layers while discarding only the self-attention layers at high resolutions, sharing key-value projections, replacing gelu with swish, fine-tune softmax into relu, trim feed-forward layers, use separable convolution, prune redundant residual blocks, reduce sampling iterations, knowledge distillation. The resulting model is able to generate 512×512 images in sub-second on mobile devices: 0.2 second on iPhone 15 Pro.
- Online Speculative Decoding by UC Berkeley, UCSD, Sisu Data, SJTU (https://arxiv.org/pdf/2310.07177.pdf). Practical speedup of speculative decoding is often impeded by the capability gap between draft and target model which can be 10-20X gap in parameters, leading to high rejection of draft predictions and fallback to more forward passes of target model. This work proposes online fine-tuning of draft model by distillation with the readily available rejected predictions. The proposed solution incorporates a replay buffer tracking logits of draft and target model, and distillation backpropagation is executed at a regular interval. Experimental results demonstrate not only significant improvement in acceptance rate, translating up to a theoretical 3X of latency reduction, but also adaptability against distribution shift in input queries.
- Token Fusion: Bridging the Gap between Token Pruning and Token Merging by Michigan State University Samsung Research America (https://arxiv.org/pdf/2312.01026.pdf).The paper introduces a method (ToFu) that combines token pruning and token merging. ToFu dynamically adapts to each layer’s properties, ensuring optimal performance based on the model’s functional linearity with respect to the interpolation in its input. Authors exploit MLERP merging technique, an enhancement over traditional average merging, inspired by the SLERP method. This approach merges tokens while preserving their norm distribution. Evaluation shows that ToFu outperforms ToMe in terms of accuracy while showing the similar performance gain at inference.
Deep Learning Software
- Medusa: Simple Framework for Accelerating LLM Generation with Multiple Decoding Heads by Together.AI. Contemporary speculative decoding solutions (Leviathan et al., Chen et al.) require multiple models (target and draft models) which often involves intricate optimization& selection of draft models to attain practical acceleration. For simplicity, Together.AI unveils a user-friendly framework, Medusa, built a top of a research work in 2018, "Block wise Parallel Decoding", with multiple enhancements. Medusa simplifies the creation of draft models without separate models by extending base model with multiple decoding heads. By keeping the base model frozen, the Medusa heads are trained in a parameter-efficient way and all on a single GPU. Medusa also features a tree-based attention mechanism for parallel evaluation of the proposed candidates, and a truncated sampling for efficient creative generation. Results and framework can be found at https://github.com/FasterDecoding/Medusa.
- HyperAttention: Long-context Attention in Near-Linear Time by Yale University and Google https://github.com/insuhan/hyper-attn. Authors propose algorithm that consists of (1) finding heavy entries inattention matrix and (2) column subsampling. For (1), authors use the sorted locality sensitive hashing (sortLSH) based on the Hamming distance. Applying sortLSH makes heavy entries in the attention matrix (sorting rows/columns) located in near diagonal hence authors do block-diagonal approximation which can be done fast. The method supports casual masking. Code is available here: https://github.com/insuhan/hyper-attn.
- Flash-Decoding for long-context inference by Stanford University. Flash Attention v1 & v2 are designed and optimized primarily for training case and exhibit low utilization of compute units when applied for LLM generation, especially for long context. As identified cause is rooted in low- batch size (query tokens) in relative to context length, Flash Decoding extends flash attention by adding 2nd-level tiling over the keys/values to improve compute utilization while retaining memory efficiency of flash attention. On A100, the micro-benchmark for multi-head attention with flash decoding kernel achieves almost constant run-time as the sequence length scales to up to 64k, translating up to 8X speedup of CodeLLaMa-34b over vanilla flash attention at very long sequences. Implementation is available at official flash attention repo & xformers.
- LLM in a flash: Efficient Large Language Model Inference with Limited Memory by Apple (https://arxiv.org/pdf/2312.11514.pdf).The paper tackles the challenge of efficiently running LLMs that exceed the available DRAM capacity by storing the model parameters on flash memory but bringing them on demand to DRAM. The method involves constructing an inference cost model that harmonizes with the flash memory behavior, guiding to optimize in two critical areas: reducing the volume of data transferred from flash and reading data in larger, more contiguous chunks. Within this flash memory-informed framework, authors introduce two principal techniques. First, “windowing” strategically reduces data transfer by reusing previously activated neurons, and second, “row-column bundling”, tailored to the sequential data access strengths of flash memory, increases the size of data chunks read from flash memory. These methods collectively enable running models up to twice the size of the available DRAM, with a 4-5x and 20-25x increase in inference speed compared to naive loading approaches in CPU and GPU, respectively.
Accelerate DIEN for Click-Through-Rate Prediction with OpenVINO™
Author: Xiake Sun, Cecilia Peng
Introduction
A click-through rate (CTR) prediction model is designed to estimate how likely a user will click on an advertisement or item. Deployment of a CTR model is considered one of the core tasks in e-commerce, as its performance not only affects platform revenue but also influences customers’ online shopping experience.
Deep Interest Evolution Network (DIEN) developed by Alibaba Group aims to better predict customer’s CTR to improve the effectiveness of advertisement display. DIEN proposes the following two modules:
- Temporally captures and extracts latent interests based on customer history behaviors.
- Models an evolving process of user interests using GRU with an attentional update gate (AUGRU)
Figure 1 shows the structure of DIEN, with the help of AUGRU, DIEN can overcome the disturbance from interest drifting, which improves the performance of CTR prediction largely in online advertising system.
DIEN Optimization with OpenVINOTM
Here we introduce DIEN optimization with OpenVINOTM in two aspects: graph level and dynamism runtime optimization.
Graph Level Optimization
Figure 2 shows the AUGRU subgraph of DIEN visualized in Netron.
OpenVINOTM implements internal operations AUGRUCell and AUGRUSequence for better graph-level optimization. Each decomposed subgraph of GRU and AUGRU is fused into a corresponding cell operator respectively. What's more, in case of static sequence length, the group of consecutive cells are further fused into a sequence operator. In case of dynamic sequence length, however, the sequence is processed with a loop of cells due to the limitation of oneDNN RNN primitive. This loop of cells is TensorIterator and (AU)GRUCell. We will introduce the optimizations of TensorIterator in next session.
TensorIterator Runtime Optimization with Dynamic Shape
Before we dive into optimization details, let’s first checkout how OpenVINOTM TensorIterator operation works.
The TensorIterator layer performs recurrent execution of thenetwork, which is described in the body, iterating through the data. Figure 3 shows the workflow of OpenVINOTM Operation TensorIterator in a simplified view. For details, please refer to the specification.
Similar to other layers, TensorIterator has regular sections: input and output. It allows connecting TensorIterator to the rest of the IR. TensorIterator also has several special sections: body, port_map, back_edges. The principles of their work are described below.
- body is a network that will be recurrently executed. The network is described layer by layer as a typical IR network.
- port_map is a set of rules to map input or output data tensors of TensorIterator layer onto body data tensors. The port_map entries can be input and output. Each entry describes a corresponding mapping rule.
- back_edges is a set of rules to transfer tensor values from body outputs at one iteration to body parameters at the next iteration. Back edge connects some Result layers in body to Parameter layer in the same body.
If output entry in the Port map doesn’t have partitioning (axis, begin, end, strides) attributes, then the final value of output of TensorIterator is the value of Result node from the last iteration. Otherwise, the final value of output of TensorIterator is a concatenation of tensors in the Result node for all body iterations.
We use Intel® VTune™ Profiler to run benchmark_app with DIEN FP32 IR model on Intel® Xeon® Gold 6252N Processor for performance profiling.
Cache internal reorder primitives in TensorIterator
Figure 4 shows that TensorIterator::prepareDynamicBackEdges() spends nearly 45% CPU time to create the reorder primitives. DIEN FP32 model has 2 TensorIterator, eachTensorIterator runs 100 iterations in body with the same input/output shape regarding the current batch. Besides, each TensorIterator has 7 back edges, which means the reorder primitive are frequently created.
So, we propose to cache internal reorder primitive in TensorIterator to optimize back edge memory copy logic. With this optimization, the performance with dynamic shape can be improved by 8x times.
Memory allocation and reuse optimization in TensorIterator
As Figure 3 shows, if we have split input as nth piece to loop in body, at the end, the outputs of TensorIterator will be a concatenation of tensors in the Result node for all body iterations, which can lead to performance overhead. Based on previous optimization we re-run performance profiling using benchmark_app with DIEN FP32 IR model on Intel® Xeon® Gold 6252N Processor as showed in Figure 5.
CPU plugin TensorIterator supports both two operators - TensorIterator and Loop. The outputs of each iteration could be concatenated and return to users. Since the output size is not always known before the execution, the legacy implementation is to dynamically allocate the concatenated output buffer.
We propose two points from the memory allocation standpoint:
- In the case of TensorIterator number of iterations is determined by the size of the axis we are slicing. So, if TensorIterator body one ach iteration will produce the same shape on output we can easily preallocate enough memory before the TI computation, The same for Loop with trip count input - we can just read the value from this input, make shape inference for the body and this determines the required amount of memory.
- More complicated story is when we don't know exact number of iterations before Loop inference (e.g., number of iterations is determined by ExecutionCondition input). In that case do the following: let’s have an output buffer where we put the Loop output. Once the buffer doesn't have enough space, we reallocate it on new size based on a simple and effective dynamic array algorithm.
OpenVINOTM implemented memory allocation and reuse optimization in TensorIterator to significantly reduce the number of reallocations and not to allocate to much memory at the same time. Experiments show that performance can be further improved by more than 20%.
DIEN OpenVINOTM Demo
Clone demo repository:
Prepare Amazon dataset:
Setup Python Environment:
Convert original TensorFlow model to OpenVINOTM FP32 IR:
Run the Benchmark with TensorFlow backend:
Run the Benchmark with OpenVINOTM backend using FP32 inference precision:
Run the Benchmark with OpenVINOTM backend using BF16 inference precision:
Please note, Xeon native supports BF16 infer precision since 4th Generation Intel® Xeon® Scalable Processors. Running BF16 on a legacy Xeon platform may lead to performance degradation.
Conclusion
In this blog, we introduce inference optimization of DIEN recommendation model with OpenVINOTM runtime as follows:
- For static input sequence length, AUGRU subgraph will be decomposed and fused as AUGRU and AUGRUSequence OpenVINOTM internal operation.
- For dynamic input sequence length, we propose cache internal reorder primitives and memory allocation and re-use optimization in TensorIterator.
- Provide a demo for model enabling and efficient inference of DIEN with OpenVINOTM runtime.
Reference
Deep Interest Evolution Network (DIEN)
Enable chatGLM by creating OpenVINO™ stateful model and runtime pipeline
Authors: Zhen Zhao(Fiona), Cheng Luo, Tingqian Li, Wenyi Zou
Introduction
Since the Large Language Models (LLMs) become the hot topic, a lot Chinese language models have been developed and actively deployed in optimization platforms. chatGLM is one of the popular Chinese LLMs which are widely been evaluated. However, ChatGLM model is not yet a native model in Transformers, which means there remains support gap in official optimum. In this blog, we provide a quick workaround to re-construct the model structure by OpenVINO™ opset contains custom optimized nodes for chatGLM specifically and these nodes has been highly optimized by AMX intrinsic and MHA fusion.
*Please note, this blog only introduces a workaround of optimization method by creating OpenVINO™ stateful model for chatGLM. This workaround has limitation of platform, which requires to use Intel® 4th Xeon Sapphire Rapids with AMX optimization. We do not promise the maintenance of this workaround.
Source link: https://github.com/luo-cheng2021/openvino/tree/luocheng/chatglm_custom/tools/gpt
To support more LLMs, including llama, chatglm2, gpt-neox/dolly, gpt-j and falcon. You can refer this link which not limited on SPR platform, also can compute from Core to Xeon:
Source link: https://github.com/luo-cheng2021/ov.cpu.llm.experimental
ChatGLM model brief
If we check with original model source of chatGLM, we can find that the ChatGLM is not compatible with Optimum ModelForCasualML, it defines the new class ChatGLMForConditionalGeneration. This model has 3 main modules (embedding, GLMBlock layers and lm_logits) during the pipeline loop, the structure is like below:
As you can see, the whole pipeline actually require model with two different graphs, the first-time inference with input prompt tokens do not require KV cache as inputs for GLMBlock layers. Since the second iteration, the previous results of QKV Attention should become the inputs of current round model inference. Along with the length of generated token increased, there will remain a lot of large sized memory copies between model inputs and outputs during pipeline inference. We can use ChatGLM6b default model configurations as an example, the memory copies between input and output arrays are like below pseudocode:
Therefore, two topics is the most important:
- How we can optimize model inference pipeline to eliminate memory copy between model inputs and outputs
- How we can put optimization efforts on GLMBlock module by reinvent execution graph
Extremely optimization by OpenVINO™ stateful model
Firstly, we need to analyze the structure of GLMBlock layer, and try to encapsulate a class to invoke OpenVINO™ opset with below workflow. Then serialize the graph to IR model(.xml, .bin).
To build an OpenVINO™ stateful model, you can refer to this document to learn.
https://docs.openvino.ai/2022.3/openvino_docs_OV_UG_network_state_intro.html
OpenVINO™ also provide model creation sample to show how to build a model by opset.
https://github.com/openvinotoolkit/openvino/blob/master/samples/cpp/model_creation_sample/main.cpp
It is clear to show that the emphasized optimization block is the custom op of Attention for chatGLM. The main idea is to build up a global context to store and update pastKV results internally, and then use intrinsic optimization for Rotary Embedding and Multi-Head Attentions. In this blog, we provide an optimized the attention structure of chatGLM with AMX intrinsic operators.
At the same time, we use int8 to compress the weights of the Fully Connected layer, you are not required to compress the model by Post Training Quantization (PTQ) or process with framework for Quantization Aware Training(QAT).
Create OpenVINO™ stateful model for chatGLM
Please prepare your hardware and software environment like below and follow the steps to optimize the chatGLM:
Hardware requirements
Intel® 4th Xeon platform(codename Sapphire Rapids) and above
Software Validation Environment
Ubuntu 22.04.1 LTS
python 3.10.11 for OpenVINO™ Runtime Python API
GCC 11.3.0 to build OpenVINO™ Runtime
cmake 3.26.4
Building OpenVINO™ Source
- Install system dependency and setup environment
- Create and enable python virtual environment
- Install python dependency
- Build OpenVINO™ with GCC 11.3.0
- Clone OpenVINO™ and update submodule
- Install python dependency for building python wheels
- Create build directory
- Build OpenVINO™ with CMake
- Install built python wheel for OpenVINO™ runtime and openvino-dev tools
- Check system gcc version and conda runtime gcc version. If the system gcc version is higher than conda gcc version like below, you should update conda gcc version for OpenVINO runtime. (Optional)
- convert pytorch model to OpenVINO™ IR
Use OpenVINO Runtime API to build Inference pipeline for chatGLM
We provide a demo by using transformers and OpenVINO™ runtime API to build the inference pipeline. In test_chatglm.py, we create a new class which inherit from transformers.PreTrainedModel. And we update the forward function by build up model inference pipeline with OpenVINO™ runtime Python API. Other member functions are migrated from ChatGLMForConditionalGeneration from modeling_chatglm.py, so that, we can make sure the input preparation work, set_random_seed, tokenizer/detokenizer and left pipelined operation can be totally same as original model source.
To enable the int8 weights compress, you just need a simple environment variable USE_INT8_WEIGHT=1. That is because during the model generation, we use int8 to compress the weights of the Fully Connected layer, and then it can use int8 weights to inference on runtime, you are not required to compress the model by framework or quantization tools.
Please follow below steps to test the chatGLM with OpenVINO™ runtime pipeline:
- Run bf16 model
- Run int8 model
Weights compression reduces memory bandwidth utilization to improve inference speed
We use VTune for performance comparison analysis of model weights bf16 and int8. Comparative analysis of memory bandwidth and CPI rate (Table 1). When model weight is compressed to int8, it can reduce memory bandwidth utilization and CPI rate.
Clockticks per Instructions Retired(CPI) event ratio, also known as Cycles per Instructions, is one of the basic performance metrics for the hardware event-based sampling collection, also known as Performance Monitoring Counter (PMC) analysis in the sampling mode. This ratio is calculated by dividing the number of unhalted processor cycles(Clockticks) by the number of instructions retired. On each processor the exact events used to count clockticks and instructions retired may be different, but VTune Profiler knows the correct ones to use.
A CPI < 1 is typical for instruction bound code, while a CPI > 1 may show up for a stall cycle bound application, also likely memory bound.
Conclusion
Along with the upgrading of OpenVINO™ main branch, the optimization work in this workaround will be generalized and integrated into official release. It will be helpful to scale more LLMs model usage. Please refer OpenVINO™ official release and Optimum-intel OpenVINO™ backend to get official and efficient support for LLMs.
Q2'24: Technology Update – Low Precision and Model Optimization
Authors
Alexander Kozlov, Nikita Savelyev, Vui Seng Chua, Souvikk Kundu, Nikolay Lyalyushkin, Andrey Anufriev, Pablo Munoz, Alexander Suslov, Liubov Talamanova, Yury Gorbachev, Nilesh Jain, Maxim Proshin
Summary
This quarter we see an increasing interest in KV-cache optimization of Large Language and Vision Models. This actually expected as KV-cache is getting a bottleneck after the weight compression problem is solved to some degree. We also believe that KV-cache optimization will continue being a hot topic as it is also involved in the Video Generations scenario where we see a lot of work going on nowadays.
Highlights
- QServe: W4A8KV4 Quantization and System Co-design for Efficient LLM Serving by MIT, NVIDIA, UMass Amherst, MIT-IBM Watson AI Lab (https://arxiv.org/pdf/2405.04532). A regular work from Song Han Lab which is a comprehensive study of deep LLM optimization and a reference design of a tool for LLM serving. The LLM optimization part includes: W4A8 and 4-bit KV-cache quantization approach; Progressive quantization of weights, to comply with 8-bit compute after dequantizing4-bit weights to 8-bits; SmoothAttention method, to reduce the error of 4-bit quantization of Key cache that is compatible with RoPE operation and can be fused into a preceding Linear layer; Progressive quantization of weights, to comply with 8-bit compute after dequantizing4-bit weights to 8-bits. The inference part contains tips and tricks to design efficient inference kernels and execution pipelines on the Nvidia GPUs. The method shows superior results comparing to competitive solutions and demonstrates the ability to substantially reduce LLM serving costs. Some code and pre-compiled binaries are available here: https://github.com/mit-han-lab/qserve.
- ZipCache: Accurate and Efficient KV Cache Quantization with Salient Token Identification by Houmo AI and Chinese universities (https://arxiv.org/pdf/2405.14256).Authors present a KV cache quantization method for LLMs. First, they construct a strong baseline for quantizing KV cache. Through the proposed channel-separable token-wise quantization scheme, the memory overhead of quantization parameters is substantially reduced compared to fine-grained group-wise quantization. To enhance the compression ratio, they propose a normalized attention score. The quantization bit-width for each token is adaptively assigned based on their saliency. The authors also develop an approximation method that decouples the saliency metric from full attention scores compatible with FlashAttention. Experiments demonstrate that the method achieves good compression ratios at fast generation speed, for example, when evaluating Mistral-7B model on GSM8k dataset, the method is capable of compressing the KV cache by 4.98×,with only a 0.38% drop in accuracy.
- BitsFusion: 1.99 bits Weight Quantization of Diffusion Model by Snap Inc. and Rutgers University (https://arxiv.org/pdf/2406.04333). The paper provides a thorough analysis of UNet weight-only quantization of Stable Diffusion 1.5 model. The authors propose an approach for mixed-precision quantization of diffusers. They quantize different layers into different bits according to their quantization error. The authors also introduce several techniques to initialize the quantized model to improve performance, including time embedding pre-computing and caching, adding balance integer, and alternating optimization for scaling factor initialization. Finally, they propose a two-stage Quantization-aware training where distillation is used at the first stage. The quantized model achieves very good results on various benchmarks. Code will be released here: https://github.com/snap-research/BitsFusion.
- Applying t-Distributions to Explore Accurate and Efficient Format[KA1] s for LLMs by Cornell University and Google (https://arxiv.org/abs/2405.03103). The paper investigates non-uniform quantization data formats by profiling the distributions of weight and activation across 30 models, including both LLM and non-LLM models. The authors discovered that Student’s t-Distribution is a better fit than the Gaussian distribution due to its flexible parameterization, which can resemble Gaussian, Cauchy, or other distributions observed indifferent neural networks. The authors derived Student Float (SF4) using a similar design process to Normal Float (NF4). SF4 outperforms NF4, FP4, and Int4 in accuracy retention across most cases and model architectures, making it a strong drop-in replacement for lookup-based datatypes like NF4. The paper proposes using SF4as a reference to extend supernormal support for existing datatypes like E2M1(one variant of FP4) and APoT4,by reassigning negative zero to a useful value, which is otherwise wasted. Additionally, the paper examines the Pareto frontier of datatypes in terms of model accuracy and MAC chip area, concluding that APoT4 and its supernormal extension are Pareto optimal for a set of models smaller than 7B parameters.
- ShiftAddLLM: MatMul-free LLM via Inference Time Reparameterization by Intel, Google Deep Mind, Google, Georgia Tech (https://arxiv.org/pdf/2406.05981).Authors developed an inference time reparameterization for traditional LLMs layers with MatMul ops to convert them to layers with Shift-Add and LUT query-based operations only. Specifically, authors quantize each weight matrix into binary matrices paired with group-wise scaling factors. The associated multiplications are reparameterized into (1) shifts between activations and scaling factors and (2) queries and adds according to the binary matrices. To reduce accuracy loss, they present a multi-objective optimization method to minimize both weight and output activation reparameterization errors. Additionally, based on varying sensitivity across layers to reparameterization, they develop an automated bit allocation strategy to further reduce memory usage and latency. The code is available at: https://github.com/GATECH-EIC/ShiftAddLLM.
Quantization
- QServe: W4A8KV4 Quantization and System Co-design for Efficient LLM Serving by MIT, NVIDIA, UMass Amherst, MIT-IBM Watson AI Lab (https://arxiv.org/pdf/2405.04532). A regular work from Song Han Lab which is a comprehensive study of deep LLM optimization and a reference design of a tool for LLM serving. The LLM optimization part includes: W4A8 and 4-bit KV-cache quantization approach; Progressive quantization of weights, to comply with 8-bit compute after dequantizing4-bit weights to 8-bits; SmoothAttention method, to reduce the error of 4-bit quantization of Key cache that is compatible with RoPE operation and can be fused into a preceding Linear layer; Progressive quantization of weights, to comply with 8-bit compute after dequantizing4-bit weights to 8-bits. The inference part contains tips and tricks to design efficient inference kernels and execution pipelines on the Nvidia GPUs. The method shows superior results comparing to competitive solutions and demonstrates the ability to substantially reduce LLM serving costs. Some code and pre-compiled binaries are available here: https://github.com/mit-han-lab/qserve.
- LQER: Low-Rank Quantization Error Reconstruction for LLMs by Imperial College London London and University of Cambridge (https://arxiv.org/pdf/2402.02446). The paper combines quantization and low-rank approximation techniques to achieve accurate and efficient LLM optimization. The method employs MXINT4 datatype (int4 + shared exponent for 4 elements) for weight quantization while quantizing activation into 8 or 6 bits with per-token scaling factors. The method also introduces 8-bit LoRA adapters to restore accuracy after weight quantization. It does not use any kind of fine-tuning. Instead, it introduces the error decomposition into two low-rank matrices. The method achieves very accurate results in W4A8 and W4A6 settings, especially on Llama-2 model family.
- LLM-QBench: A Benchmark Towards the Best Practice for Post-training Quantization of Large Language Models by Beihang University, SenseTime Research, and Nanyang Technological University (https://arxiv.org/pdf/2405.06001).The paper focuses on identifying the most effective practices for quantizing LLMs, with the goal of balancing performance with computational efficiency. Fora fair analysis, the authors develop a quantization toolkit LLMC and design four crucial principles considering the inference efficiency, quantized accuracy, calibration cost, and modularization. By benchmarking on various models and datasets with over 500 experiments, three takeaways corresponding to calibration data, quantization algorithm, and quantization schemes are derived. Finally, a best practice of LLM PTQ pipeline is constructed. All the benchmark results and the toolkit can be found at https://github.com/ModelTC/llmc.
- SKVQ: Sliding-window Key and Value Cache Quantization for Large Language Models Houmo AI by Houmo AI and Chinese universities (https://arxiv.org/pdf/2405.06219). The paper addresses the problem of extremely low bit-width KV cache quantization. To achieve this, it proposes a method that rearranges the channels of the KV cache in order to improve the similarity of channels in quantization groups and applies clipped dynamic quantization at the group level. Additionally, the method ensures that the most recent window tokens in the KV cache are preserved with high precision. This helps maintain the accuracy of a small but important portion of the KV cache. Evaluation on LLMs demonstrates that the method surpasses previous quantization approaches, allowing for quantization of the KV cache to 2-bit keys and 1.5-bit values with minimal loss of accuracy. The code is available at https://github.com/cat538/SKVQ.
- Integer Scale: A Free Lunch for Faster Fine-grained Quantization of LLMs by Meituan (https://arxiv.org/pdf/2405.14597). The paper proposes a scheme to use integer scales when computing dot products of W4A8quantized LLMs. It allows keeping group scales for weights in the integer precision as well and using INT32 buffer as the accumulator of partial dot products. An additional floating point scale is required and applied to the super-group of dot products between weights and activations. It brings the proposed method close to the known double quantization approach. The paper provides extensive evaluation data for Llama2 and Llama3 models showing close results to the baseline floating-point scales.
- Mitigating Quantization Errors Due to Activation Spikes in GLU-Based LLMs by Hanyang University (https://arxiv.org/pdf/2405.14428).The paper aims at reducing the accuracy degradation of fully-quantized LLM models (both weights and activations are quantized). Authors propose two empirical methods, Quantization-free Module (QFeM) and Quantization-free Prefix (QFeP), to isolate the activation spikes during quantization that cause most of the accuracy drop. Essentially, they propose a way to identify what layers are more error-prone and keep these layers in the floating-point precision. The code is available at https://github.com/onnoo/activation-spikes.
- AdpQ: A Zero-shot Calibration Free Adaptive Post Training Quantization Method for LLMs by Huawei Noah Lab and McGill University (https://arxiv.org/pdf/2405.13358).This paper presents a novel zero-shot adaptive PTQ method for LLMs that does not require any calibration data. Inspired by Adaptive LASSO regression model, the authors proposed approach that tackles the challenge of outlier activations by separating salient weights using an adaptive soft-thresholding method. Guided by Adaptive LASSO, this method ensures that the quantized weights distribution closely follows the originally trained weights and eliminates the need for calibration data entirely. The method achieves good results at much faster quantization time.
- PTQ4SAM: Post-Training Quantization for Segment Anything by Beihang University (https://arxiv.org/pdf/2405.03144).A practical study on quantization of the Segment Anything model. The authors observe a challenging bimodal distribution for quantization and analyze its characteristics. To overcome it, they propose a Bimodal Integration (BIG)strategy, which automatically detects it and transforms the bimodal distribution to normal distribution equivalently. They also present the Adaptive Granularity Quantization which represents diverse post-Softmax distributions accurately with appropriate granularity. Experiments show that the method can achieve good results even in low-bit quantization settings (6 or4 bits). Code is available at https://github.com/chengtao-lv/PTQ4SAM.
- QNCD: Quantization Noise Correction for Diffusion Models by Kuaishou Technology (https://arxiv.org/pdf/2403.20137). Authors identify two primary quantization challenges for Duffusion models: intra and inter quantization noise. Intra quantization noise, exacerbated by embeddings in the resblock module, extends activation quantization ranges, increasing disturbances in each single denoising step. Besides, inter quantization noise stems from cumulative quantization deviations across the entire denoising process, altering data distributions step-by-step. Authors propose embedding-derived feature smoothing for eliminating intra quantization noise and a runtime noise estimation module for dynamically filtering inter quantization noise. Experiments demonstrate that the method achieves good results in W4A8 and W8A8 quantization settings on ImageNet (LDM-4). Code is available at: https://github.com/huanpengchu/QNCD.
- SliM-LLM: Salience-DrivenMixed-Precision Quantization for Large Language Models by The ETH Zürich, University of Hong Kong, and Beihang University (https://arxiv.org/pdf/2405.14917).The paper focuses on the problem of ultra-low bit weight quantization of LLMs. Specifically, it proposes the method relies on two novel techniques: (1)Salience-Determined Bit Allocation utilizes the clustering characteristics of salience distribution to allocate the bit-widths of each quantization group. This increases the accuracy of quantized LLMs and maintains the inference efficiency high; (2) Salience-Weighted Quantizer Calibration optimizes the parameters of the quantizer by considering the element-wise salience within the group. The method is evaluated in two setups for quantization parameters tuning: greedy search and gradient based search. Evaluation shows good results on Llama 1/2/3 models. Code is available at https://github.com/Aaronhuang-778/SliM-LLM.
- LCQ: Low-Rank Codebook based Quantization for Large Language Models by Nanjing University (https://arxiv.org/pdf/2405.20973). The paper proposes a method for LLM optimization using customized low-ranking codebooks the rank of which can be larger than one, for quantization. A gradient-based optimization algorithm is proposed to optimize the parameters of the codebook. The method also adopts a double quantization strategy for compressing the parameters of the codebook, which can reduce the storage cost of the codebook. Experiments show that achieves better accuracy than existing methods with a negligibly extra storage cost.
- P2 -ViT: Power-of-Two Post-Training Quantization and Acceleration for Fully Quantized Vision Transformer by Nanjing University and Sun Yat-sen University (https://arxiv.org/pdf/2405.19915). The paper introduces a Power-of-Two (PoT) post-training quantization and acceleration framework for ViT models. The authors analyze ViTs’ properties and develop a dedicated quantization scheme. This scheme incorporates techniques such as adaptive PoT rounding and PoT Aware smoothing, allowing for the efficient quantization of ViTs with PoT scaling factors. By doing this, computationally expensive floating-point multiplications and divisions with in the re-quantization process can be traded with hardware-efficient bitwise shift operations. Furthermore, we introduce a coarse-to-fine automatic mixed-precision quantization methodology for better accuracy-efficiency trade-offs. Finally, authors build a dedicated accelerator engine to better everage our algorithmic properties for enhancing hardware efficiency. Code is available at: https://github.com/shihuihong214/P2-ViT.
- QJL: 1-Bit Quantized JLTransform for KV Cache Quantization with Zero Overhead by New York University and Adobe Research (https://arxiv.org/pdf/2406.03482).The paper studies problems of KV-cache quantization of LLMs, specifically the Key part as it is more error-prone when lowering its precision. Authors propose an approach that consists of a Johnson-Lindenstrauss (JL) transform followed by sign-bit quantization for Key cache. They introduce an asymmetric estimator for the inner product of two vectors and demonstrate that applying the method to one vector and a standard JL transform without quantization to the other provides an unbiased estimator with minimal distortion. They also developed a CUDA-based implementation for optimized computation. When applied across various LLMs and NLP tasks to quantize the KV cache to only 3 bits, the method demonstrates a more than fivefold reduction in KV cache memory usage without an insignificant accuracy drop. Codes will be available at https://github.com/amirzandieh/QJL.
- ViDiT-Q: Efficient and Accurate Quantization of Diffusion Transformers for Image and Video Generation by Tsinghua University, Infinigence AI, 3Microsoft, and Shanghai Jiao Tong University (https://arxiv.org/pdf/2406.02540).The paper tackles the problems of accurate quantization of diffusion vision transformer models. Essentially, authors apply dynamic 8-bit per-token quantization to activations. They also propose to smooth activation with a Smoothquant-like approach but with different α factors tuned to each iteration of the diffusion process. Finally, authors propose to select a per-layer weight bit-width (e.g.W4A8, W6A6, or W8A8) depending on the sensitivity and position of the layer in the Transformer block. All these tricks lead to very good accuracy results in the image and video generation tasks.
- Instance-Aware Group Quantization for Vision Transformers by Yonsei University and Articron (https://arxiv.org/pdf/2404.00928). In this paper an approach for instance-aware group quantization for ViTs(IGQ-ViT) is introduced. According to the approach, channels of activation maps are dynamically split into multiple groups where each group has its own set of quantization parameters. Authors also extend their scheme to quantize softmax attentions across tokens. IGQ-ViT demonstrates superior accuracy results across image classification, object detection and instance segmentation task. Authors claim that performance overhead induced by dynamic quantization is no more than 4% compared to layer-wise quantization.
- Reg-PTQ: Regression-specialized Post-training Quantization for Fully Quantized Object Detector by Beihang University (https://openaccess.thecvf.com/content/CVPR2024/papers/Ding_Reg-PTQ_Regression-specialized_Post-training_Quantization_for_Fully_Quantized_Object_Detector_CVPR_2024_paper.pdf). In this paper authors explore full quantization of object detection models contrary to most existing approaches which quantize only detection backbones and keep detection head in original precision. Based on the findings, the reason behind poor quantization of detector heads is that they are optimized to solve regression tasks. Specifically, authors argue that (1) regressors are more sensitive to perturbation compared to classifiers, (2) minimizing quantization error does not necessarily result in optimal scaling factors for regressor and(3) regressors weights follow non-uniform distribution contrary to classifiers. To tackle these problems a novel Reg-PTQ method is introduced. Based on the results it achieves 7.6x and 5.4x reduction in computation and storage consumption under INT4 precision with little performance degradation.
- Towards Accurate Post-training Quantization for Diffusion Models (https://openaccess.thecvf.com/content/CVPR2024/papers/Wang_Towards_Accurate_Post-training_Quantization_for_Diffusion_Models_CVPR_2024_paper.pdf). In this paper authors propose a method for accurate post-training quantization of diffusion models. The main idea is to split diffusion timesteps for each layer into groups where each group corresponds to its own set of quantization parameters. Such split is obtained by minimizing some optimization objective on a calibration dataset. Besides this, a special timestep selection method is employed for sampling timesteps for calibration. Overall, the method demonstrates superior generation quality results over such baselines as LSQ, PTQ4DM and Q-Diffusion.
Pruning/Sparsity
- Effective Interplay between Sparsity and Quantization: From Theory to Practice by Google and EcoCloud (https://arxiv.org/pdf/2405.20935). Authors provide the theoretical analysis of how sparsity and quantization interact. Mathematical proofs establish that applying sparsity before quantization (S → Q) is the optimal sequence for compression. Authors demonstrate that sparsity and quantization are not orthogonal operations. Combining them introduces additional errors beyond the sum of their individual errors. They validate theoretical findings through experiments covering a diverse range of models, including prominent LLMs (OPT, LLaMA) and ViTs. The code will be published at: https://github.com/parsa-epfl/quantization-sparsity-interplay.
- Prompt-prompted Mixture of Experts for Efficient LLM Generation by CMU (https://arxiv.org/pdf/2404.01365). Authors introduce GRIFFIN, a training-free MoE that selects unique FF experts at the sequence level for efficient generation across a plethora of LLMs with different non-ReLU activation functions. This is possible due to a critical observation that many trained LLMs naturally produce highly structured FF activation patterns within a sequence, which we call flocking. Despite the method’s simplicity, it shows with 50% of the FF parameters, GRIFFIN maintains the original model’s performance with little to no degradation on a variety of classification and generation tasks, all while improving latency (e.g. 1.25× speed-up in Llama 213B on an NVIDIA L40). Code is available at https://github.com/hdong920/GRIFFIN.
- Sparse maximal update parameterization: A holistic approach to sparse training dynamics by Cerebras Systems (https://arxiv.org/pdf/2405.15743).This paper addresses the common issue in sparse training where hyper parameters from dense training are reused, leading to suboptimal convergence, and requiring extensive tuning for different sparsity ratios. The researchers introduce a novel sparse training methodology called Sparse Maximal Update Parameterization (SuPar), which extends the maximal update parameterization (uP)to sparse training. SuPar involves reparameterizing (see Table 1) weight initialization and learning rates relative to changes in sparsity, effectively preventing exploding or vanishing signals and maintaining stable activation, gradient, and weight update scales across varying sparsity levels and model widths. SuPar reparameterization is remarkable, it allows zero-shot hyperparameter transfer, i.e. practitioners can now tune small proxy models(dense/sparse) and transfer optimal HPs directly to models at scale for any model sparsity, thus enhancing the efficiency and reducing the cost of sparse model development. Experiments demonstrate that SμPar sets the Pareto frontier best loss across all sparsities and widths, including large dense model with width equal to GPT-3 XL.
- Sparse Expansion and Neuronal Disentanglement by MIT, IST Austria, Neural Magic (https://arxiv.org/pdf/2405.15756). Sparse Expansion is an approach of converting dense LLMs to mixture of sparse experts to attain inference efficiency. The method begins with applying dimensionality reduction (PCA) on the inputs of FFN linear layers, followed by a k-means clustering. The intuition is that tokens within a cluster share a sparse expert better without significant distortion. SparseGPT is then used to create a sparse expert for each cluster group. During inference, the PCA and k-means models act as routers, directing tokens to the appropriate sparse expert based on their cluster. While this increases the overall model size, acceleration is achieved through the conditional execution of experts and the sparse execution of these experts, with minimal cost for the routers. The paper includes layer-wise speedup benchmarks and shows that Sparse Expansion outperforms other one-shot sparsification approaches in perplexity for the same inference FLOP budget per token. A significant portion of the paper is dedicated to the concept of neuron entanglement, explaining, and quantifying the efficacy of sparse expansion.
- MULTIFLOW: Shifting Towards Task-Agnostic Vision-Language Pruning by University of Trento and Cisco Research (https://arxiv.org/pdf/2404.05621). Authors highlight that existing techniques for pruning of Visual-Language models(VLMs) are task-specific and propose a task-agnostic method for pruning VLMs. The proposed Multimodal Flow Pruning framework has the following properties: (1) the importance of a weight is computed based on saliency of the neurons it connects; and (2) parameters are pruned considering features of which modality they are used to compute allowing to avoid pruning too much from a single modality and too little from another. Experiments show that the proposed MULTIFLOW method outperforms recent more sophisticated competitors.
Other methods
- Flash Diffusion: Accelerating Any Conditional Diffusion Model for Few Steps Image Generation by Jasper Research (https://arxiv.org/pdf/2406.02347). The paper proposes a LoRA-compatible distillation method aiming at reducing the number of sampling steps required to generate high-quality samples from a trained diffusion model. Authors emphasize the versatility of the method through an extensive experimental study across various tasks (text-to-image, image inpainting, super-resolution, face-swapping), diffusion model architectures (SD1.5, SDXL and Pixart-α) and illustrate its compatibility with adapters. The method is relatively lightweight and can optimize SD1.5 model with 2 Nvidia H100 80GB with 13 hours of fine-tuning. Code is available at https://github.com/gojasper/flash-diffusion.
- GaLore: Memory-Efficient LLM Training by Gradient Low-Rank Projection by California Institute of Technology, Meta AI, University of Texas at Austin, and Carnegie Mellon University (https://arxiv.org/pdf/2403.03507). The paper introduces a Gradient Low-Rank Projection (GaLore), a training strategy that allows full-parameter learning but is more memory-efficient than common low-rank adaptation methods such as LoRA. The idea is to use PCA after a number of training steps to obtain a gradient projection matrix and use it to get a low-rank gradient matrix that is used for weights update. The approach reduces memory usage by up to 65.5% in optimizer states while maintaining both efficiency and performance for pre-training. 8-bit GaLore further reduces optimizer memory by up to 82.5% and total training memory by 63.3%, compared to a BF16 baseline. It demonstrates the feasibility of pre-training a 7B model on consumer GPUs with 24GB memory. The code is available at: https://github.com/jiaweizzhao/GaLore.
- MiniCache: KV Cache Compression in Depth Dimension for Large Language Models by ZIP Lab of Monash and Zhejiang University (https://arxiv.org/pdf/2405.14366).The authors propose a training-free KV cache compression technique by merging KV tokens across every two consecutive transformer layers, based on the observation that KV tokens are highly similar across depth, especially from the middle to the last transformer layers. Specifically, a pair of K/V projections from two consecutive layers can be encoded into respective scaling factors and a shared directional vector computed via Spherical Linear Interpolation(SLERP). To address the information loss from merging dissimilar tokens, the algorithm uses angular-based distance to filter KV positions for retention. The algorithm is straightforward, involving calibration of only two hyperparameters, and it has demonstrated to enhance a 4X compressed KV cache by4-bit quantization to over 5X compression while retaining reasonable accuracy of instruction-tuned Mistral, LLama2-7B across benchmarks.
- Scalable MatMul-free Language Modeling by University of California, Soochow University, LuxiTech (https://arxiv.org/pdf/2406.02528). Authors develop a MatMul-free language model by using additive operations in dense layers and element-wise Hadamard products for self-attention-like functions. Specifically, ternary weights eliminate MatMul in dense layers, similar to BNNs. To remove MatMul from self-attention, they optimize the Gated Recurrent to rely solely on element-wise products and show that this model competes with state-of-the-art Transformers while eliminating all MatMul operations. To quantify the hardware benefits of lightweight models, the authors provide an optimized GPU implementation in addition to a custom FPGA accelerator. By using fused kernels in the GPU implementation of the ternary dense layers, training is accelerated by 25.6% and memory consumption is reduced by up to 61.0% over an unoptimized baseline on GPU. Furthermore, by employing lower-bit optimized CUDA kernels, inference speed is increased by 4.57 times, and memory usage is reduced by a factor of 10 when the model is scaled up to 13B parameters. The code is available at https://github.com/ridgerchu/matmulfreellm.
- Unlocking Efficiency in Large Language Model Inference: A Comprehensive Survey of Speculative Decoding by Hong Kong Polytechnic, Peking University, Microsoft Research Asia and Alibaba (https://arxiv.org/abs/2401.07851). While LLMs are proliferating over the past two years, Speculative Decoding (SD) has emerged as a crucial paradigm to accelerate autoregressive generation. This survey is among the first to provide a comprehensive introduction and overview of the state of the art in SD, highlighting key developments in this space. A main contribution of this work is the introduction of Spec-Bench, a unified benchmark for evaluating SD methods across standardized subtasks such as multi-turn conversation, summarization, RAG, translation, question answering, and mathematical reasoning. The codes and benchmarks for various SD methods on RTX 3090 and A100 GPUs are accessible for further exploration and validation.
- Speculative Decoding via Early-exiting for Faster LLM Inference with Thompson Sampling Control Mechanism by Meituan and Meta AI (https://arxiv.org/pdf/2406.03853).The paper introduces an early-exiting framework for generating draft tokens, which allows a single LLM to fulfill the drafting and verification stages. The model is trained using self-distillation. The authors conceptualize the generation length of draft tokens as a multi-armed bandit problem and propose a control mechanism based on Thompson Sampling, which leverages sampling to devise an optimal strategy. They conducted experiments on three benchmarks and showed that the method can significantly improve the model’s inference speed.
- LayerSkip: Enabling Early Exit Inference and Self-Speculative Decoding by Meta, University of Toronto, Carnegie Mellon University, University of Wisconsin-Madison, Dana-Farber Cancer Institute (https://arxiv.org/pdf/2404.16710).Authors research the idea of early exit in LLMs for speculative decoding. First, during training, they apply layer dropout, with low dropout rates for earlier layers and higher dropout rates for later layers, and an early exit loss where all transformer layers share the same exit. Second, during inference, they show that this training recipe increases the accuracy of early exit at earlier layers, without adding any auxiliary layers or modules to the model. Third, they present a self-speculative decoding solution where we exit at early layers and verify and correct with remaining layers of the model. They run experiments on different Llama model sizes on different types of training: pretraining from scratch, continual pretraining, finetuning on specific data domain, and finetuning on specific task, and show speedups of up to 2.16× on summarization for CNN/DM documents, 1.82× on coding, and 2.0× on TOPv2 semantic parsing task.
Software
- INT4 Decoding GQA CUDA Optimizations for LLM Inference by Meta(https://pytorch.org/blog/int4-decoding).The authors provide a comprehensive study and ten practical steps, including KV-cache quantization, to improve the performance of Grouped-query Attention. All these optimizations result in performance improvements of up to 1.8x on the NVIDIA A100 GPU and 1.9x on the NVIDIA H100 GPU.
- torchao: PyTorch Architecture Optimization by Meta (https://github.com/pytorch/ao). PyTorch library for quantization and sparsity. Currently-available features contain full models quantization, INT8, INT4, MXFP4,6,8 weight-only quantization and efficient model fine-tuning with GaLore method.
- Introducing Apple’s On-Device and Server Foundation Models by Apple (https://machinelearning.apple.com/research/introducing-apple-foundation-models). Apple has established a set of pre-trained and optimized models for its HW. The claim is that 3B LLM model can be run at 30t/s on iPhone 15 Pro. In terms of optimizations that are being used, authors claim weight palletization to 2 and 4 bits, quantization of embeddings and activations and efficient Key-Value (KV) cache update. They use their own AXLearn library built on top of JAX and XLA for model pre-training and fine-tuning.
- BitBLAS by Microsoft (https://github.com/microsoft/BitBLAS).A library to support mixed-precision BLAS operations on GPUs. BitBLAS aims to support efficient mixed-precision DNN model deployment, especially the quantization in large language models (LLMs), for example, the 𝑊4𝐴16 in GPTQ, the 𝑊2𝐴16 in BitDistiller, the 𝑊2𝐴8 in BitNet-b1.58.