CHARM+: Cross-Hardware Attention with Re-Merge Multistream Mechanism

Authors: Xinhang Zhang , Boning Zhang , Chengchun Liu , Chunpu Li , Lei Sun , Weifeng Zhang , Limin Xiao

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Abstract: As sequence lengths continue to grow, distributed attention based on sequence parallel (e.g., Ring-Attention) has become a mainstream solution for large language models (LLMs). Nevertheless, inherent communication dependencies limit computation-communication overlap, reducing GPU utilization. Moreover, in cross-hardware (NUMA or node) architectures, due to imbalanced communication bandwidth, frequent communication synchronization will limit overall performance. Based on these insights, we propose CHARM+, Cross-Hardware Attention with Re-Merge Multistream Mechanism. We reorganize sequential communications into several levels and achieve intra-level parallelism and computation overlap. Furthermore, we decouple cross-hardware communication from intra-hardware communication, eliminating synchronization overhead caused by bandwidth imbalance. Forward and backward algorithms were evaluated on multiple hardware architectures and consistently outperformed state-of-the-art methods. Compared to Ring-Attention, our forward and backward algorithms achieve average speedups of 1.3x and 1.7x on a dual-NUMA PCIe architecture, and 2.8x and 2.9x on a dual-node NVLink architecture, respectively.

Comments:

Accepted to NeurIPS 2026 (Poster)

Subjects:

Artificial Intelligence (cs.AI) ; Hardware Architecture (cs.AR); Distributed, Parallel, and Cluster Computing (cs.DC)

Cite as:

arXiv:2611.05906 [cs.AI]

(or

arXiv:2611.05906v1 [cs.AI] for this version)

https://doi.org/10.48550/arXiv.2611.05906

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arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Boning Zhang [ view email ]

[v1]

Wed, 4 Nov 2026 03:57:56 UTC (758 KB)

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