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Prototype rate-distortion KV cache eviction plus quantization #5

Description

@randomvariable

Idea

Prototype a vLLM experiment based on RDKV: jointly choose KV-cache eviction and quantization under a memory budget rather than treating KV compression and eviction as separate policies.

Target Hardware

  • DGX Spark / GB10 / sm121
  • Strix Halo / RDNA 3.5 / gfx1151

Sources

  • https://arxiv.org/abs/2605.08317v1 (RDKV: joint eviction + quantization under budget)
  • https://arxiv.org/abs/2608.05326 (QEvict: three-tier recoverable eviction — full-precision hot windows, a quantized recoverable tier with dequantize-and-promote on attention reactivation, deletion only for lowest-confidence windows; motivated by attention-importance drift during decode. 2026-08-07 scan: mechanism genuinely absent — fork eviction is positional/structural only, vllm/v1/core/kv_cache_manager.py:593-625, with no score-driven policy and no recoverable tier. Watch; the decode-time attention-score tap is the hard part since fused decode kernels do not expose per-block scores.)

Why It Might Matter

Both GB10 and Strix Halo are memory-capacity and memory-bandwidth constrained for long-context decode. A joint eviction/quantization policy could reduce KV memory footprint and bandwidth while preserving more useful context than uniform KV quantization or simple eviction heuristics.

Possible vLLM Work

  • Read the RDKV algorithm and identify the smallest integration point in vLLM's KV cache manager or scheduler.
  • Start with an offline trace/replay experiment over existing request/KV metadata before touching hot kernels.
  • Compare against existing KV quantization/eviction behavior on long-context decode workloads.
  • Gate any prototype behind a clear experimental flag and measure accuracy/perplexity impact.

Duplicate Check

Searched randomvariable/vllm issues by title keywords, arXiv ID 2605.08317, RDKV, and the stable paper title phrase; no existing equivalent issue was found.

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