[Scheduler] Pre match radix tree in schedule

[juncaipeng]

Motivation

提前匹配GPU Cache，只要block足够用于没命中缓存的token，降低多轮长请求调度的门槛。

💡 If this PR is a Cherry Pick, the PR title needs to follow the format by adding the [Cherry-Pick] label at the very beginning and appending the original PR ID at the end. For example, [Cherry-Pick][CI] Add check trigger and logic(#5191)

💡 如若此PR是Cherry Pick，PR标题需遵循格式，在最开始加上[Cherry-Pick]标签，以及最后面加上原PR ID，例如[Cherry-Pick][CI] Add check trigger and logic(#5191)

Modifications

新增pre_match_block_on_gpu
调整调用get_prefix_cached_blocks前面的判断

Usage or Command

Accuracy Tests

Checklist

• Add at least a tag in the PR title.
  • Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
  • You can add new tags based on the PR content, but the semantics must be clear.
• Format your code, run pre-commit before commit.
• Add unit tests. Please write the reason in this PR if no unit tests.
• Provide accuracy results.
• If the current PR is submitting to the release branch, make sure the PR has been submitted to the develop branch, then cherry-pick it to the release branch with the [Cherry-Pick] PR tag.

[paddle-bot]

Thanks for your contribution!

[Copilot]

Pull request overview

该 PR 在 V1 调度流程中引入“提前在 GPU 前缀树上做只读匹配”的预检查，以便在调用 get_prefix_cached_blocks() 之前，先评估是否有足够 GPU blocks 覆盖未命中的 token，从而降低长请求多轮调度时因层级缓存匹配带来的资源门槛。

Changes:

• 新增 PrefixCacheManager.pre_match_block_on_gpu()：只读遍历 radix tree，计算 GPU resident 的前缀命中 token 数。
• 在 ResourceManagerV1.schedule() 与 preallocate_resource_in_p() 中，使用预匹配结果计算 need_block_num 后再做 can_allocate_gpu_blocks() 判断。
• 微调 request_match_blocks() 中 CPU cache 预备阶段的条件分支，避免对 0 blocks 做无意义的 can_allocate 检查。

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
fastdeploy/engine/sched/resource_manager_v1.py	在调度/预分配前加入 GPU 前缀预匹配后的 block 预算检查，减少层级缓存匹配导致的调度门槛/死锁风险。
fastdeploy/cache_manager/prefix_cache_manager.py	新增 GPU-only 预匹配方法，并调整 CPU cache 分配判断逻辑。

[codecov-commenter]

Codecov Report

❌ Patch coverage is 32.60870% with 31 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@5e469fc). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/cache_manager/prefix_cache_manager.py	12.50%	28 Missing ⚠️
fastdeploy/engine/sched/resource_manager_v1.py	78.57%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #6989   +/-   ##
==========================================
  Coverage           ?   73.79%           
==========================================
  Files              ?      399           
  Lines              ?    56085           
  Branches           ?     8854           
==========================================
  Hits               ?    41389           
  Misses             ?    11770           
  Partials           ?     2926           

Flag	Coverage Δ
GPU	73.79% <32.60%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.