SemiAnalysis: sparse attention fixes memory bandwidth, not memory capacity
AccBalanced · x · 2026-10-18
SemiAnalysis clarifies a common misconception about sparse attention: it addresses the memory bandwidth bottleneck, not memory capacity.
Key points
- Sparse attention doesn't mitigate the memory capacity bottleneck — it's a technique that helps a lot with bandwidth
- HiCache's idea is to offload KV cache from HBM to a lower-tier, higher-capacity but lower-bandwidth memory, loading only the most relevant tokens during computation
- But sparse attention still has to select tokens, so you can't discard any context; at some point everything still has to be loaded into HBM
- That's where HiSparse helps: applying typical caching rules so only the most relevant parts get loaded into HBM
Essential reading for anyone running long-context inference and designing KV cache tiering.
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