feat: add lora config for dpo dtensor backend

[RayenTian]

Result

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Summary by CodeRabbit

• New Features

  • Introduced Low-Rank Adaptation (LoRA) configuration options with customizable parameters for model optimization

• Tests

  • Expanded functional test coverage with new DPO workflow tests including LoRA-based scenarios to ensure reliability

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds LoRA configuration options to the DPO example configuration file and introduces new functional GPU tests, including a test script for LoRA-based automodel DPO training with comprehensive test orchestration including metric validation.

Changes

Cohort / File(s)	Summary
LoRA Configuration examples/configs/dpo.yaml	Adds new LoRA settings block under policy.dtensor_cfg with parameters: enabled, target_modules, exclude_modules, match_all_linear, dim, alpha, dropout, dropout_position, lora_A_init, and use_triton
Test Registration tests/functional/L1_Functional_Tests_GPU.sh	Registers two new functional tests: dpo_automodel_lora.sh and dpo_megatron.sh in the GPU test suite execution sequence
New Test Script tests/functional/dpo_automodel_lora.sh	Implements end-to-end DPO LoRA test orchestration: environment setup, runs DPO automodel training with LoRA enabled, captures metrics to JSON, and validates training loss at step 3 is below 0.8

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• feat: Megatron SFT LoRA #1629 — Adds and expands LoRA configuration under policy.dtensor_cfg and introduces LoRA-focused functional tests

Suggested labels

CI:L1

Suggested reviewers

• terrykong
• yuki-97
• joyang-nv

🚥 Pre-merge checks | ✅ 2 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Test Results For Major Changes	⚠️ Warning	PR introduces major changes but PR description lacks documented test results, convergence validation, or performance information despite adding functional tests.	Update PR description with: (1) Results from running dpo_automodel_lora.sh and dpo_megatron.sh tests including training loss and convergence, (2) Confirmation of no regression in numerics/convergence, (3) Performance measurements. Fix bash syntax error in line 11: change set -eou pipefail to set -euo pipefail.
Title check	❓ Inconclusive	The PR title mentions adding a LoRA config for DPO dtensor backend, which aligns with the primary change (adding LoRA configuration to dpo.yaml), but conflicts with PR objectives that describe SFT (supervised fine-tuning) configuration.	Clarify whether the PR is for LoRA or SFT configuration. The title says 'lora config' but the PR objectives mention 'SFT config.' Update the title and objectives to be consistent.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing touches

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Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@tests/functional/dpo_automodel_lora.sh`:
- Line 11: The shell script uses an incorrectly ordered set invocation "set -eou
pipefail" where the -o flag's argument must immediately follow, causing an
invalid option; update the command to "set -euo pipefail" so -e and -u are
enabled and -o pipefail is applied (replace the existing set -eou pipefail
invocation).