[Disagg][Perf] Use NPU event sync instead of blocking tolist to avoid unintentional copy ops blocking across different NPU streams, improving disagg TTIT/TTFT

[jesse996]

This PR is based on top of vllm-project/vllm#22760

What this PR does / why we need it?

When we copy the sampled valid token ids from device to host, avoid using tolist which would trigger a CUDA wise stream sync if the source is on device. We change it to use non-blocking copy followed by an explicit CUDA event sync.

Does this PR introduce any user-facing change?

How was this patch tested?

Bring up vLLM server

VLLM_USE_V1=1 vllm serve Qwen/Qwen2.5-14B-Instruct --disable-l
og-requests -tp 8 --max-num-seqs 64 --no-enable-prefix-caching --max_num_batched_tokens=8000

Before：

After

As shown in the figure, the TTFT decreased

• vLLM version: v0.10.2
• vLLM main: vllm-project/vllm@9607d5e

[github-actions]

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[gemini-code-assist]

Code Review

This pull request introduces a valid performance optimization by replacing a blocking .tolist() call with a non-blocking D2H copy and an NPU event synchronization. This is a good approach to avoid device-wide stalls. However, there is a critical bug in the implementation where the pre-allocated pinned memory tensor is sized incorrectly and uses an undefined attribute, which will cause a runtime error. I've provided a fix for this issue.

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.36%. Comparing base (1bbb20e) to head (5be58d5).
⚠️ Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
vllm_ascend/worker/model_runner_v1.py	60.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2788      +/-   ##
==========================================
+ Coverage   74.76%   75.36%   +0.59%     
==========================================
  Files         150      155       +5     
  Lines       20891    21350     +459     
==========================================
+ Hits        15620    16091     +471     
+ Misses       5271     5259      -12     

Flag	Coverage Δ
unittests	75.36% <95.00%> (+0.59%)	⬆️

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[wangxiyuan]

nice work, can you print the benchmark result with/without this PR to make sure it works as expect?

[jesse996]

nice work, can you print the benchmark result with/without this PR to make sure it works as expect?

added to the beginning

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[wangxiyuan]

can you rewrite the comment to ascend case?

[jesse996]

updated