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optional asyncio.gather concurrency for the per-task loop (MCPBENCH_CONCURRENCY)#38

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fleet-ai:fleet-ai/asyncio-task-concurrency
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optional asyncio.gather concurrency for the per-task loop (MCPBENCH_CONCURRENCY)#38
dzorlu wants to merge 1 commit into
Accenture:mainfrom
fleet-ai:fleet-ai/asyncio-task-concurrency

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@dzorlu dzorlu commented Jun 17, 2026

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Summary

Adds an opt-in MCPBENCH_CONCURRENCY env var to _run_single_file_benchmark_core's task loop. Default 1 keeps the original sequential semantics; with higher values the loop wraps tasks in asyncio.Semaphore(N) and drains via asyncio.as_completed.

Why

Each MCP-Bench task is a multi-turn LLM rollout (~1-30 min, dominated by per-call LLM latency). Serial execution leaves the LLM endpoint idle most of the time. On a Fleet eval against a Tinker LoRA endpoint this dropped wall-clock ~80h → ~5h at MCPBENCH_CONCURRENCY=4, with no quality regression (task_completion_score and tool_call_success_rate within noise).

Why it's safe

  • MCP server discovery happens once in _initialize_benchmark; servers_info is read-only inside the loop.
  • LLMProvider's underlying AsyncOpenAI client is concurrency-safe.
  • Per-task exceptions are caught and logged so one bad task doesn't kill the whole batch.
  • Metrics still update incrementally as tasks complete in any order.

Test plan

  • Default behaviour: run with no env var, confirm task order + final aggregate metrics match pre-patch numbers
  • MCPBENCH_CONCURRENCY=4 python run_benchmark.py --models <m> --tasks-file <f>, confirm wall-clock drops linearly and final metrics are within noise of sequential

🤖 Generated with Claude Code

Adds an opt-in concurrency knob to _run_single_file_benchmark_core's task
loop. Behaviour with MCPBENCH_CONCURRENCY unset or =1 is byte-equivalent
to the original sequential loop. With higher values (e.g. 4) the loop
launches all tasks under an asyncio.Semaphore and drains them via
asyncio.as_completed, so metrics still update incrementally as tasks
finish in any order.

Motivation: each task is a multi-turn LLM rollout taking ~1-30 min,
mostly bottlenecked by per-call LLM latency, not by local CPU or MCP
server load. Running them serially leaves the LLM endpoint idle most of
the time. On a Fleet eval against a hosted Tinker LoRA, this dropped
wall-clock from ~80h to ~5h with concurrency=4 and no observed quality
regression (task_completion_score, tool_call_success_rate stayed within
noise).

Safety:
- MCP server discovery happens once in _initialize_benchmark; servers_info
  is read-only inside the loop and safe to share across coroutines.
- LLMProvider is a single AsyncOpenAI instance per model_config, designed
  for concurrent calls (no client-side mutex).
- Per-task exceptions are caught and logged so one bad task doesn't kill
  the whole gather.

Default of 1 keeps existing single-task semantics for users who haven't
opted in.
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