Stream-CQSA: Resolving Memory Bottlenecks in Attention Computation via Flexible Workload Scheduling

This article introduces the Stream-CQSA framework, a novel attention computation method based on the Cyclic Quorum Set (CQS) theory. Its core value lies in enabling precise attention computation for billion-token sequences on a single GPU via streaming processing and flexible workload scheduling—without altering the mathematical definition of attention—effectively addressing the quadratic memory bottleneck of self-attention mechanisms in long-context large language models.

Long-context large language models have great potential, but the memory consumption of self-attention mechanisms scales quadratically with sequence length (O(N²)), leading to frequent out-of-memory (OOM) errors when processing long sequences. Existing memory optimization methods reduce complexity but implicitly assume that Q, K, V tensors must fit into device memory—an assumption that fails for billion-token sequences.

The core innovation of Stream-CQSA is the CQS Divide operation, derived from the Cyclic Quorum Set (CQS) theory in distributed system consensus protocols. It decomposes the attention computation of a full sequence into local computations of multiple independent sub-sequence blocks, and these local results can be precisely reconstructed into the global attention result (without approximation errors) via specific combination rules. The mathematical foundation is the linearity of attention operations, which allows the global softmax to be obtained through weighted combination of local softmax values.

The Stream-CQSA framework implements memory-adaptive scheduling with the following process:

1. Memory Analysis: Evaluate available GPU memory to determine the maximum sub-sequence block size;
2. Task Decomposition: Split attention computation into sub-tasks according to memory budget;
3. Streaming Execution: Execute sub-tasks sequentially, with outputs temporarily stored in CPU memory or disk;
4. Result Reconstruction: Combine sub-task results according to CQS rules. The framework flexibly adapts to different memory budgets, and sub-tasks can be executed in parallel across devices.

Experimental validation shows:

• Stream-CQSA's memory usage is proportional to the sub-sequence block size (instead of the square of sequence length);
• It successfully completes precise attention computation for billion-token sequences on a single consumer-grade GPU (traditional methods would OOM). Computational overhead is mainly caused by data movement, but this can be effectively hidden via GPU asynchronous execution and high-bandwidth memory, with acceptable end-to-end latency gaps.

Stream-CQSA has far-reaching impacts on AI infrastructure:

• Reduces reliance on distributed multi-card systems, making single-card deployment cheaper, simpler, and more reliable;
• Enables long-context processing on edge AI devices (smartphones, embedded systems), facilitating privacy protection and real-time responses;
• Aligns well with near-memory computing architectures, providing directions for future optimization of dedicated AI chips.

Stream-CQSA has limitations:

• Currently only supports standard self-attention; needs to be extended to variants like sparse and linear attention;
• The optimal sub-task scheduling strategy depends on hardware and workloads, requiring an automatic tuning mechanism. Future directions include applying CQS theory to other Transformer components (feed-forward networks, layer normalization) to address more memory bottlenecks in long-sequence scenarios.

Stream-CQSA is an important step in the engineering of long-context large language models. It translates CQS theory into a practical system architecture, proving that precise attention computation and memory efficiency can coexist. As AI applications demand longer context lengths, such innovations will pave the way for the deployment of next-generation intelligent systems.