feat: Replace legacy spillover logic with Waterfall LRU architecture #219
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This is a major architectural upgrade to the core benchmark logic. Replacing the original "Spillover" memory management strategy with the new "Waterfall LRU" implementation to accurately simulate enterprise storage hierarchies. Key Changes: - Waterfall Eviction: Implemented recursive eviction (GPU -> CPU -> NVMe). New data now correctly lands in the fastest available tier, pushing cold data down, rather than the old behavior where new data skipped directly to NVMe if RAM was full. - Static Buffer Optimization: Replaced the CPU-bound np.random generation with a pre-allocated static noise buffer. This removes the CPU bottleneck that was masking true storage latency, allowing us to fully saturate high-performance NVMe drives. - Concurrency Hardening: Added semaphore-based concurrency limits (max_concurrent_allocs) and atomic memory reservations to prevent OOM crashes under heavy load. - Storage Metrics: Added explicit tracking for nvme_tokens_processed to calculate true storage throughput separate from system throughput. - Stress Test Validation: Verified that this new architecture correctly exposes storage latency limits (e.g., pushing P95 write latency >1000ms) where the old script artificially throttled the load.
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This patch addresses two bugs that surface when running the benchmark with --enable-rag: 1. Race condition in process_requests (line 2693) Worker threads begin processing requests immediately upon benchmark start, while RAG document ingestion runs in a separate daemon thread. When a worker hits the 10% RAG query path before any documents have been ingested, random.choice() is called on an empty list, raising IndexError. Fixed by adding a truthiness check on self.rag_manager.documents before entering the RAG code path. An empty dict evaluates to False, so RAG queries are safely skipped until ingestion populates at least one document. 2. Division by zero in KVCacheGenerator.generate (line 1097) The buffer slicing logic uses modulo to compute a pseudo-random start index: seed % (buffer_size - total_elements). When total_elements exactly equals buffer_size (an edge case permitted by the <= guard), the divisor becomes zero, raising ZeroDivisionError. Fixed by computing the divisor separately and defaulting start_idx to 0 when the divisor is zero.
… 4G of DRAM to reduce Queue contention and unrealistic read amplification
idevasena
approved these changes
Dec 19, 2025
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This is a major architectural upgrade to the core benchmark logic. Replacing the original "Spillover" memory management strategy with the new "Waterfall LRU" implementation to accurately simulate enterprise storage hierarchies.
Key Changes: