modelscope--ms-swift/docs/source_en/Megatron-SWIFT/GKD.md

GKD

If you are new to GKD/OPD-RL, please refer to the distillation documentation first.

GKD (Generalized Knowledge Distillation) is a training method that transfers knowledge from a teacher model to a student model by computing the Jensen-Shannon Divergence (JSD) loss between their output distributions.

Feature Support

Megatron GKD currently supports the following features:

• Training Modes: Full parameter training and LoRA fine-tuning
• Parallelism Strategies: Context Parallel (CP), Pipeline Parallel (PP), Tensor Parallel (TP), and Expert Parallel (EP)
• Model Support: Compatible with LLMs and MLLMs in Megatron-SWIFT
• Teacher Offload: Supports offloading teacher model to CPU to save GPU memory
• Online Generation: Supports on-policy generation using vLLM for student model
• Multi-turn Training: Supports multi-turn GKD via --multi_turn_scheduler, sharing the same MultiTurnScheduler infrastructure as GRPO.

Parameters

GKD-specific Parameters

Parameter	Type	Default	Description
--teacher_model	str	-	Path or model ID of the teacher model *Can be omitted when using teacher_model_server
--teacher_model_server	str	None	Teacher API URL; single URL or multi-teacher JSON. See distillation docs
--teacher_tag_key	str	"dataset"	Column name for matching sample tags to teacher tags in multi-teacher routing
--gkd_logits_topk	int	None	Number of Top-K logits; required when using external API
--beta	float	0.5	JSD divergence interpolation coefficient: • 0.0: Forward KL • 0.5: Symmetric JSD • 1.0: Reverse KL
--lmbda	float	0.5	On-Policy learning probability: • 0.0: Pure Off-Policy • 1.0: Pure On-Policy
--temperature	float	0.9	Temperature for sampling and loss computation
--sft_alpha	float	0	Mix in a proportion of SFT loss; applied to non-student-generated completions
--max_completion_length	int	512	Maximum tokens for generation

Batch-related Parameters

Same as Megatron SFT, use the following parameters to control batch size:

Parameter	Description
--micro_batch_size	Training batch size per DP group
--global_batch_size	Global batch size: micro_batch_size × dp_size × gradient_accumulation_steps

Reference

For more parameters, please refer to Command-line Parameters

For training scripts, please refer to Megatron GKD Scripts

Training script using Teacher Server reference here