DiffuSeq-v2: Bridging Discrete and Continuous Text Spaces for Accelerated Seq2Seq Diffusion Models
Summary
Seq2Seq text diffusion models such as DiffuSeq produce good text, but they train slowly and generate slowly. They also usually rely on Minimum Bayes Risk (MBR) decoding over several samples to reach good quality. DiffuSeq-v2 speeds up both training and generation by combining continuous and discrete noise.
During training, the model first adds Gaussian noise in embedding space. It then randomly swaps some target-token vectors for a learned "soft absorbing state", a trainable vector that plays a role similar to a [MASK] token. The swap probability is scaled with the timestep, and the model learns to remove both kinds of corruption together. The same discrete noise is applied at sampling time, which brings training and inference closer together. Because of this, the clamping step is no longer needed and the DPM-solver++ ODE sampler can be used.
On the QQP paraphrase benchmark, the method converges more than 4× faster in total training time. Without MBR, it matches the quality of DiffuSeq with MBR. A 2-step variant generates about 800× faster than single-sample DiffuSeq while scoring higher. This moves diffusion-based text generation closer to practical use.
Key points
- Training speed: FP16 alone cut training from 28 to 11 hours on 2 A100 GPUs (about 2.5×). The soft absorbing state made convergence at least 1.75× faster, for more than 4× overall.
- Quality without MBR: On QQP, the full 2000-step version reaches BLEU 0.2411, close to DiffuSeq with MBR=10 (0.2413).
- 2-step speedup: The 2-step DPM-solver++ version scores BLEU 0.2115 versus 0.1884 for DiffuSeq (MBR=1), a 12.3% relative gain. Its throughput is 406.5 it/s versus 0.51 it/s, roughly 800× faster.
- Other baselines: The method beats the continuous baseline BG-DiffuSeq. Compared with discrete models (Multinomial, D3PM-absorbing), it remains competitive and has a clear advantage in generation speed. Reparameterized discrete variants (RDM) were not directly compared, and RDM+absorbing reaches higher BLEU than the 2-step version.
- Ablations:
- Removing clamping costs DiffuSeq 3.4% BLEU but the new model only 0.5%.
- Leaving out the discrete noise at sampling time cuts BLEU by 14.9%.
- A [MASK] ratio of γ = 0.5 worked best.
- Limitations: The method was tested only on QQP, with no translation or summarization experiments and no study of larger models. Code is available in the
diffuseq-v2branch of Shark-NLP/DiffuSeq.
Cite
@inproceedings{gong2023diffuseq,
title = {{DiffuSeq-v2: Bridging Discrete and Continuous Text Spaces for Accelerated Seq2Seq Diffusion Models}},
author = {Gong, Shansan and Li, Mukai and Feng, Jiangtao and Wu, Zhiyong and Kong, Lingpeng},
booktitle = {Findings of the Association for Computational Linguistics: EMNLP 2023},
year = {2023},
doi = {10.18653/v1/2023.findings-emnlp.660},
eprint = {2310.05793},
archivePrefix = {arXiv},
url = {https://doi.org/10.18653/v1/2023.findings-emnlp.660}
}References
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