[None][fix] Use all reusable blocks for MAX_UTILIZATION token budget - #15065
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[None][fix] Use all reusable blocks for MAX_UTILIZATION token budget#15065brb-nv wants to merge 1 commit into
brb-nv wants to merge 1 commit into
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getNeededBlocksOneStep (MAX_UTILIZATION) derived estimatedReusableTokens from reusableBlocksAllocated (active-ref blocks only), the same conservative count correctly used for the block/capacity budget since NVIDIA#11731. In steady state, prefixes from completed requests are free-but-cached (no refs), so reusableBlocksAllocated drops to ~0 while reusableBlocksAll stays large. The micro batch scheduler then under-credits reuse, FCFS charges full context chunks, one request saturates max_num_tokens, and context requests serialize to ~1/iter -- inflating TTFT at high concurrency. Decouple the two budgets in getNeededBlocksOneStep: - Block/capacity budget keeps reusableBlocksAllocated (avoids the NVIDIA#11731 double-count / over-admission). - Token/compute budget now uses reusableBlocksAll, since cached KV is recovered via prepopulatedPromptLen regardless of ref state. This mirrors the accounting getRemainingBlocksToCompletion already uses for GUARANTEED_NO_EVICT, removing the discrepancy between the two policies. Signed-off-by: Balaram Buddharaju <169953907+brb-nv@users.noreply.github.com>
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Description
getNeededBlocksOneStep(MAX_UTILIZATION) derivedestimatedReusableTokensfromreusableBlocksAllocated(active-ref blocks only), the same conservative count correctly used for the block/capacity budget since #11731. In steady state, prefixes from completed requests are free-but-cached (no refs), soreusableBlocksAllocateddrops to ~0 whilereusableBlocksAllstays large. The micro batch scheduler then under-credits reuse, FCFS charges full context chunks, one request saturates max_num_tokens, and context requests serialize to ~1/iter -- inflating TTFT at high concurrency.Decouple the two budgets in
getNeededBlocksOneStep:reusableBlocksAllocated(avoids the [None][fix] Fix overly aggressive capacity scheduler #11731 double-count / over-admission).reusableBlocksAll, since cached KV is recovered viaprepopulatedPromptLenregardless of ref state.This mirrors the accounting
getRemainingBlocksToCompletionalready uses for GUARANTEED_NO_EVICT, removing the discrepancy between the two policies.Test Coverage
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