[https://nvbugs/5453667] [fix] reverting a breaking change: make trtllm-bench enable_chunked_context defaults backend-dependent

[venkywonka]

• Restores the state to original intent of [https://nvbugs/5355007][fix] Set enable_chunked_context as True by default in trtllm bench #6582 - ie, chunking should be disabled by default in pytorch backend and enabled by default in trt backend.
• Currently we enabled chunking by default in both trt and pyt backend, that has caused some regressions in pytorch backend.

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Summary by CodeRabbit

• New Features

  • Simplified throughput benchmark CLI: replaced dual --enable/--disable chunked context flags with a single --enable_chunked_context flag. Omitting the flag now uses a backend-specific default.
  • Backend-aware defaults: chunked context is enabled by default for TensorRT backend and disabled for others when not specified.

• Documentation

  • CLI help updated to clarify the new flag behavior and per-backend defaults.

[coderabbitai]

📝 Walkthrough

Walkthrough

Refactors the throughput CLI option for chunked context to a single tri-state flag (--enable_chunked_context). If not provided, the code derives the default from the backend (True for TensorRT, False otherwise) and applies it to exec_settings["settings_config"]["chunking"].

Changes

Cohort / File(s)	Summary of Changes
CLI flag refactor and backend-based defaulting tensorrt_llm/bench/benchmark/throughput.py	Replaced dual boolean flags with a single is_flag option defaulting to None; added runtime logic to set default based on backend; updated help text; applied resolved value to settings_config.chunking.

Sequence Diagram(s)

sequenceDiagram
  participant User
  participant CLI as throughput CLI
  participant Cmd as throughput_command
  participant Cfg as exec_settings.settings_config

  User->>CLI: run throughput with/without --enable_chunked_context
  CLI->>Cmd: parsed enable_chunked_context (None/True)
  Cmd->>Cmd: if None: set based on backend == "tensorrt"
  Cmd->>Cfg: set chunking = resolved value
  Cmd->>Cmd: proceed with benchmark execution

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• [https://nvbugs/5355007][fix] Set enable_chunked_context as True by default in trtllm bench #6582: Also changes enable_chunked_context in the same file, setting a hard default True; overlaps with this PR’s tri-state and backend-derived default.

Suggested reviewers

• nv-yilinf
• kaiyux
• FrankD412

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (2)

tensorrt_llm/bench/benchmark/throughput.py (2)

237-242: Tri-state flag is good; keep backwards compatibility and clarify the help

Nice restoration of backend-derived defaults. To avoid breaking existing scripts that still pass --disable_chunked_context, consider keeping the dual-form boolean flag while setting default=None for the tri-state behavior. Also, this option is a runtime execution toggle rather than a reporting option; consider moving it under the "Engine run configuration" group in a follow-up for better UX.

Apply this diff to restore the dual-form flag (preserves old UX) while keeping tri-state defaulting:

-@optgroup.option(
-    "--enable_chunked_context",
-    is_flag=True,
-    default=None,
-    help="Enable chunking in prefill stage for enhanced throughput benchmark. "
-    "Default is False for PyTorch/AutoDeploy backend, True for TensorRT backend.",
-)
+@optgroup.option(
+    "--enable_chunked_context/--disable_chunked_context",
+    default=None,
+    help=(
+        "Enable/disable chunking in prefill stage for throughput benchmarking. "
+        "Omit this flag to use the backend-specific default: "
+        "False for PyTorch/_autodeploy, True for TensorRT."
+    ),
+)

---

353-356: Make typing reflect tri-state and log the resolved value

Since the CLI param can be None, the local typing should be Optional[bool]. A short log line helps diagnose which default applied at runtime.

-    enable_chunked_context: bool = params.get("enable_chunked_context")
-    if enable_chunked_context is None:
-        # Set default based on backend: True for TensorRT, False for others
-        enable_chunked_context = backend.lower() == "tensorrt"
+    enable_chunked_context: Optional[bool] = params.get("enable_chunked_context")
+    decision_source = "CLI" if enable_chunked_context is not None else f"backend default ({backend})"
+    if enable_chunked_context is None:
+        # Set default based on backend: True for TensorRT, False for others
+        enable_chunked_context = backend.lower() == "tensorrt"
+    logger.info(f"Chunked-context: {enable_chunked_context} [{decision_source}]")

Add this import near the top of the file:

from typing import Optional

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[venkywonka]

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