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Any-Precision LLM: Low-Cost Deployment of Multiple, Different-Sized LLMs
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Proposes any-precision LLMs, obtained by incrementally upscaling a 3-bit SqueezeLLM seed model into a single parent model whose bit-prefixes serve 3–8-bit models, plus a bitplane-based GPU kernel that reduces memory traffic at lower bit-widths.
Problem
Deploying multiple LLMs of different sizes multiplies memory cost and training cost, and prior any-precision DNN methods require QAT from scratch and do not reduce memory bandwidth for LLM inference.
Approach
Incremental upscaling: starting from a low-bit non-uniform (clustering-based) PTQ seed model, each cluster is split into two sub-clusters per added bit, so lower-bit models are bit-prefixes of the parent; paired with a bitplane weight layout and GPU kernel that loads only the required bitplanes.
Key results
- Incremental upscaling from a 3-bit SqueezeLLM seed yields 4–8-bit models whose perplexity is nearly identical to independently quantized SqueezeLLM models (increase <0.1 in most cases on Llama-2-7B).
- Serving {3,4,6,8} bits for Llama-2-7B needs 7.9 GB versus 19.1 GB for separate deployment (2.41x memory savings).
- The kernel achieves up to 3.99x speedup over cuBLAS FP16 at 3-bit on RTX 4090 for a (1,4096)x(4096,4096) matvec, matching or beating the SqueezeLLM kernel on desktop and laptop GPUs and outperforming it on Jetson AGX Orin.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| incremental upscaling of SqueezeLLM from 3-bit seed (vs independently quantized) | SqueezeLLM · Wikitext2/PTB/C4 perplexity, Llama-2-7B, OPT, Mistral | perplexity: <0.1 in most cases | No clear effect |
| incremental upscaling of SqueezeLLM from 3-bit seed | SqueezeLLM · zero-shot average accuracy, five tasks | accuracy: within 0.2% | No clear effect |
| incremental upscaling applied to uniform GPTQ (ablation) | GPTQ · Wikitext2 perplexity, Llama-2-7B 4-bit | perplexity: 5.68 -> 36.82 | Hurt |
| incremental upscaling applied to uniform AWQ (ablation) | AWQ · Wikitext2 perplexity, Llama-2-7B 4-bit | perplexity: 5.59 -> INF | Hurt |
| bitplane-based kernel with weight bitplane layout optimization, bit-transpose and table merging vs SqueezeLLM kernel | any-precision GEMV kernel · matvec speedup vs cuBLAS FP16, RTX 4090 and Jetson AGX Orin | speedup: on par on RTX 4090/4070 Laptop; substantially faster on Jetson (e.g. 3.02x vs 1.94x at 4-bit) | Mixed |
| table lookup merging for 3-bit (merging two 3-bit indices into one 6-bit lookup) (ablation) | any-precision kernel 3-bit · kernel microbenchmark ablation | speedup | Helped |
| weight bitplane layout optimization, improved bit-transpose (ablation) | any-precision kernel · kernel microbenchmark ablation | speedup | Helped |
| end-to-end integration of the any-precision engine into TensorRT-LLM | Llama-2-7B · end-to-end throughput, RTX 4090 and RTX 4070 Laptop | throughput | Helped |
Surprising findings
- Incremental upscaling applied to GPTQ and AWQ (uniform methods) fails, with perplexities exploding (e.g., INF) at 4-bit, motivating the use of non-uniform quantization.
- Seed-model quantization plus upscaling takes under a minute (51.8 s for Llama-2-7B) on a CPU without any training.
Limitations
- Custom kernel does not use tensor cores, so it becomes slower than cuBLAS FP16 for large batch sizes such as prefill; the engine falls back to separate dequantization for M above about 16.
- Upscaled models at 4-bit can lose accuracy on some tasks (e.g., OPT-6.7B WinoGrande -2.3 pp change in some settings) and the method is evaluated only on 1.3B–7B models.
- Uniform quantization methods (GPTQ, AWQ) are incompatible with incremental upscaling, restricting the choice of backbone to non-uniform quantization.
Experimental setup
Datasets: WikiText2 C4 Penn Treebank
Benchmarks: WikiText2 PTB C4 ARC-easy ARC-challenge HellaSwag PIQA WinoGrande
Metrics: perplexity zero-shot accuracy matrix-vector latency end-to-end throughput memory footprint
Baselines: SqueezeLLM AWQ GPTQ LUT-GEMM ExLlamaV2 TensorRT-LLM cuBLAS FP16
Builds on: SqueezeLLM any-precision DNN AWQ GPTQ LUT-GEMM
Closest papers by meaning
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