[v1][feature] add dpo trainer (#10544)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

tests_v1/trainers/test_fsdp2_dpo_trainer.py

@@ -0,0 +1,97 @@
+# Copyright 2025 the LlamaFactory team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+
+@pytest.mark.xfail(reason="CI machines may OOM when heavily loaded.")
+@pytest.mark.runs_on(["cuda", "npu"])
+def test_fsdp2_dpo_trainer(tmp_path: Path):
+    """Test FSDP2 DPO trainer with sigmoid loss by simulating `llamafactory-cli dpo config.yaml`."""
+    config_yaml = """\
+model: Qwen/Qwen3-0.6B
+trust_remote_code: true
+model_class: llm
+
+template: qwen3_nothink
+
+kernel_config:
+    name: auto
+    include_kernels: auto
+
+quant_config: null
+
+dist_config:
+    name: fsdp2
+    dcp_path: null
+
+init_config:
+    name: init_on_meta
+
+# PEFT Configuration
+peft_config:
+    name: lora
+    r: 8
+    lora_alpha: 16
+    lora_dropout: 0.0
+    target_modules: all
+
+### data
+train_dataset: data/v1_dpo_demo.yaml
+
+### training
+output_dir: {output_dir}
+micro_batch_size: 1
+global_batch_size: 1
+cutoff_len: 2048
+learning_rate: 1.0e-4
+bf16: false
+max_steps: 1
+pref_loss: sigmoid
+pref_beta: 0.1
+dpo_label_smoothing: 0.0
+
+### sample
+sample_backend: hf
+max_new_tokens: 128
+"""
+    # Create output directory
+    output_dir = tmp_path / "outputs"
+    output_dir.mkdir(parents=True, exist_ok=True)
+    config_file = tmp_path / "config.yaml"
+    config_file.write_text(config_yaml.format(output_dir=str(output_dir)))
+
+    # Set up environment variables
+    env = os.environ.copy()
+    env["USE_V1"] = "1"  # Use v1 launcher
+    env["FORCE_TORCHRUN"] = "1"  # Force distributed training via torchrun
+
+    # Run the CLI command via subprocess
+    result = subprocess.run(
+        [sys.executable, "-m", "llamafactory.cli", "dpo", str(config_file)],
+        env=env,
+        capture_output=True,
+        cwd=str(Path(__file__).parent.parent.parent),  # LLaMA-Factory root
+    )
+
+    # Decode output with error handling (progress bars may contain non-UTF-8 bytes)
+    stderr = result.stderr.decode("utf-8", errors="replace")
+
+    # Check the result
+    assert result.returncode == 0, f"DPO training failed with return code {result.returncode}\nSTDERR: {stderr}"