FOCUS: DLLMs Know How to Tame Their Compute Bound

Kaihua Liang¹, Xin Tan², An Zhong¹, Hong Xu², Marco Canini¹

¹King Abdullah University of Science and Technology    ²The Chinese University of Hong Kong

Design Overview

FOCUS is an inference system for diffusion LLMs (DLLMs) built on top of the LMDeploy engine. It targets a key compute-bound bottleneck in block-diffusion decoding: models compute over a full token block each step, yet only a small fraction of tokens are actually decodable.

Using attention-derived token importance delta from early layers, this training-free solution predicts which tokens are likely decodable and evicts non-decodable ones on the fly to avoid redundant computation, increasing the effective batch size and enabling scalable throughput. FOCUS achieves up to 3.52× throughput improvement without compromising quality across benchmarks. This repo contains the LMDeploy-based implementation for SDAR and LLaDA2.0-mini.

Efficiency Improvement

Key Implementation Files (FOCUS)

Based on LMDeploy, the main FOCUS-related implementations are in:

• lmdeploy/pytorch/kernels/cuda/focus.py: Triton kernels for importance scoring, target selection, and state compaction.
• lmdeploy/pytorch/kernels/cuda/pagedattention.py: attention kernels (including ragged paged attention).
• lmdeploy/pytorch/kernels/cuda/fill_kv_cache.py: KV-cache fill kernels (including sparse KV fill for paged attention).
• lmdeploy/pytorch/models/sdar.py: FOCUS eviction integrated into SDAR layers.
• lmdeploy/pytorch/models/llada2.py: FOCUS eviction integrated into LLaDA2.0-mini layers.
• lmdeploy/pytorch/strategies/dllm/sequence.py: FocusState tracking and per-step statistics.
• lmdeploy/pytorch/strategies/dllm/model_inputs.py: focus-specific inputs for DLLM batches.
• lmdeploy/pytorch/model_inputs.py: focus runtime view and host/device synchronization.
• lmdeploy/pytorch/engine/inputs_maker.py: builds focus masks and pinned buffers for delayed cache batches.
• lmdeploy/pytorch/engine/model_agent.py: propagates processed positions back to the scheduler.

Install (CUDA)

FOCUS relies on Triton CUDA kernels and is intended for CUDA GPUs. LMDeploy's default prebuilt wheels target CUDA 12 (since v0.3.0); RTX 50-series GPUs require CUDA 12.8 wheels. CUDA 11+ is supported when building from source, but ensure your local CUDA toolkit matches your PyTorch/Triton stack. We have only tested FOCUS flow with Python 3.13; other Python versions 3.9-3.12 should also work but are not covered by our tests.

1. Create and activate a Python environment.
2. Install runtime dependencies:

pip install -r requirements/runtime_cuda.txt

3. Install the repo using the PyTorch engine:

DISABLE_TURBOMIND=1 pip install -e .

Benchmarking

All scripts write logs to ./results. Run them from the repo root.

• FOCUS throughput: benchmark/run_focus_throughput_evaluation.sh

  benchmark/run_focus_throughput_evaluation.sh <dataset_id> <model_id> [alpha]

  Example:

  benchmark/run_focus_throughput_evaluation.sh anon8231489123/ShareGPT_Vicuna_unfiltered JetLM/SDAR-8B-Chat-b32
  benchmark/run_focus_throughput_evaluation.sh anon8231489123/ShareGPT_Vicuna_unfiltered JetLM/SDAR-8B-Chat-b32 1.8

• LMDeploy throughput: benchmark/run_baseline_throughput_evaluation.sh

  benchmark/run_baseline_throughput_evaluation.sh <dataset_id> <model_id>

  Example:

  benchmark/run_baseline_throughput_evaluation.sh anon8231489123/ShareGPT_Vicuna_unfiltered JetLM/SDAR-8B-Chat-b32

• Block size comparison for SDAR: benchmark/run_block_size_comparison.sh

  benchmark/run_block_size_comparison.sh <dataset_id>

  This runs SDAR models JetLM/SDAR-8B-Chat-b16 and JetLM/SDAR-8B-Chat-b64 for both FOCUS and Base settings.

• Delayed cache baseline for SDAR: benchmark/run_sdar_delayed_cache_benchmark.sh

  benchmark/run_sdar_delayed_cache_benchmark.sh <dataset_id>

  This runs JetLM/SDAR-8B-Chat-b32 with delayed cache enabled and FOCUS disabled.

Dataset notes:

• dataset_id can be a HuggingFace dataset ID or a local JSON/JSONL path supported by benchmark/profile_throughput.py.
• HuggingFace dataset IDs require the datasets package and network access.

Generation Quality Testing

For generation quality evaluation of SDAR/LLaDA2.0-mini models, see opencompass-0.5.1.post1/README.md for OpenCompass benchmarking instructions with either HuggingFace/Transformers or LMDeploy backends.

Citation

If you find FOCUS useful in your work, please cite:

@article{liang2026focus,
  title   = {FOCUS: DLLMs Know How to Tame Their Compute Bound},
  author  = {Kaihua Liang and Xin Tan and An Zhong and Hong Xu and Marco Canini},
  journal = {arXiv preprint arXiv:2601.23278},
  year    = {2026},
  url     = {https://arxiv.org/abs/2601.23278}
}

Acknowledgements

FOCUS builds on and/or includes code and models from:

• LMDeploy
• OpenCompass (vendored snapshot under opencompass-0.5.1.post1/)
• SDAR: JetAstra/SDAR | weights: JetLM/SDAR-8B-Chat-b16, JetLM/SDAR-8B-Chat-b32, JetLM/SDAR-8B-Chat-b64
• LLaDA2.0: inclusionAI/LLaDA2.0 | weights: inclusionAI/LLaDA2.0-mini