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jchandra

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High-Fidelity KV Cache Summarization Using Entropy and Low-Rank Reconstruction

jchandra.com
64 points·by jchandra·3 mesi fa·17 comments

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jchandra
·3 mesi fa·discuss
Yeah, that’s consistent. topK keeps the obvious tokens, but subtle context gets eroded over time rather than dropped all at once.
jchandra
·3 mesi fa·discuss
Fair point, the gap isn’t huge in that plot, and both degrade at low ratios. The difference is more in how they degrade: TopK can have sharper, localized failures, while HAE tends to be a bit more smooth. That doesn’t always show up strongly in average MSE.

That said, the gains are modest right now, this is still a research prototype exploring the tradeoff, and there’s clearly more work to be done.
jchandra
·3 mesi fa·discuss
Thanks, really appreciate the pointer. Will dig into it.
jchandra
·3 mesi fa·discuss
Haha, that’s a very fair reading :)

Yeah, the latency hit is definitely real. That said, most of what I’ve run so far is CPU-bound, which likely exaggerates it quite a bit so I didn’t want to draw strong conclusions from that.

Would need proper GPU implementations to really understand where it lands.
jchandra
·3 mesi fa·discuss
I completely agree.Right now this is all on a synthetic setup to isolate the behavior and understand the reconstruction vs memory tradeoff. Real models will definitely behave differently.

I’ve started trying this out with actual models, but currently running things CPU-bound, so it’s pretty slow. Would ideally want to try this properly on GPU, but that gets expensive quickly

So yeah, still very much a research prototype — but validating this on real models/data is definitely the next step.
jchandra
·3 mesi fa·discuss
That’s a great point and yeah, I’d agree SVD itself isn’t new at all.

On downsides: definitely a few. The biggest one is latency - SVD is fairly heavy, so even though it’s amortized (runs periodically, not per token), it still adds noticeable overhead. It’s also more complex than simple pruning, and I haven’t validated how well this holds on real downstream tasks yet.

This is very much a research prototype right now more about exploring a different tradeoff space than something ready for production.
jchandra
·3 mesi fa·discuss
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jchandra
·3 mesi fa·discuss
In this prototype, OLS + SVD isn’t per-token, it runs only when the recycle bin fills (amortized over multiple tokens).

That said, it’s still heavier than Top-K. I haven’t benchmarked end-to-end latency yet; this is mainly exploring the accuracy vs memory tradeoff.
jchandra
·3 mesi fa·discuss
I’ve been exploring KV cache optimization for LLM inference.

Most methods (Top-K, sliding window) prune tokens. This works on average, but fails selectively — a few tokens cause large errors when removed.

I tried reframing the problem as approximating the attention function: Attn(Q, K, V)

Prototype: - entropy → identify weak tokens - OLS → reconstruct their contribution - SVD → compress them

Early results show lower error than Top-K at low memory, sometimes even lower memory overall.

This is still a small research prototype, would appreciate feedback or pointers to related work.