feat: add SGLang rollout backend, part1

examples/configs/grpo_math_1B_sglang.yaml

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+# GRPO Algorithm Configuration
+grpo:
+  num_prompts_per_step: 32
+  num_generations_per_prompt: 16
+  max_rollout_turns: 1 
+  max_num_epochs: 1
+  max_num_steps: 1000000
+  normalize_rewards: true
+  use_leave_one_out_baseline: true
+  val_period: 10
+  val_at_start: false
+  overlong_filtering: false
+  max_val_samples: 256
+  val_batch_size: 128
+  seed: 42
+  use_dynamic_sampling: false
+  dynamic_sampling_max_gen_batches: 10
+  batch_multiplier: 1
+  reward_shaping:
+    enabled: false
+    overlong_buffer_length: 128
+    overlong_buffer_penalty: 1
+    max_response_length: ${policy.max_total_sequence_length}
+  reward_scaling:
+    enabled: false
+    source_min: 0.0
+    source_max: 1.0
+    target_min: 0.0
+    target_max: 1.0
+
+  async_grpo:
+    enabled: false # Set to true to enable async training mode
+    # Max age (in training steps) for trajectories used in training
+    max_trajectory_age_steps: 1
+    in_flight_weight_updates: false # Set to true to enable in-flight weight updates
+    recompute_kv_cache_after_weight_updates: false # Set to true to recompute kv cache after in-flight-weight-updates
+
+loss_fn:
+  reference_policy_kl_penalty: 0.01
+  # Can be set to k1, k2, k3
+  # For more details, see http://joschu.net/blog/kl-approx.html
+  reference_policy_kl_type: "k3"
+  kl_input_clamp_value: 20.0
+  kl_output_clamp_value: 10.0
+  ratio_clip_min: 0.2
+  ratio_clip_max: 0.2
+  ratio_clip_c: null
+  # (default off) loss formulation improvements (docs/guides/grpo.md#loss)
+  use_on_policy_kl_approximation: false
+  # Async GRPO requires importance sampling correction enabled
+  # Set to true when async_grpo.enabled is true
+  use_importance_sampling_correction: false
+  truncated_importance_sampling_ratio: null
+  sequence_level_importance_ratios: false
+  token_level_loss: true
+
+checkpointing:
+  enabled: true
+  checkpoint_dir: "results/grpo"
+  metric_name: "val:accuracy" # one of "val:" or "train:" followed by the metric name
+  higher_is_better: true
+  keep_top_k: 3
+  save_period: 10
+  checkpoint_must_save_by: null
+  model_save_format: "safetensors"
+  save_consolidated: false
+
+policy:
+  model_name: "Qwen/Qwen2.5-1.5B"
+  tokenizer:
+    name: ${policy.model_name} ## specify if you'd like to use a tokenizer different from the model's default
+    chat_template_kwargs: null # can be used to pass kwargs to the chat template, e.g., enable_thinking=true
+  hf_config_overrides: {} 
+  train_global_batch_size: 512
+  train_micro_batch_size: 4
+  generation_batch_size: 32 # Only used when generating using HF backend
+  logprob_batch_size: 4
+  max_total_sequence_length: 512
+  precision: "bfloat16"
+  logprob_chunk_size: null
+  offload_optimizer_for_logprob: false # Only useful for non-colocated generation since colocated generation will always offload optimizer to cuda before refit
+
+  dtensor_cfg:
+    _v2: true
+    enabled: true
+    cpu_offload: False
+    sequence_parallel: false
+    activation_checkpointing: false
+    tensor_parallel_size: 1
+    context_parallel_size: 1
+    custom_parallel_plan: null
+
+  megatron_cfg:
+    enabled: false
+    empty_unused_memory_level: 1  # 1 is the minimum recommendation for RL since we almost always need to offload before beginning generation. Setting to 0 is faster, but you are more likely to run out of GPU memory.
+    activation_checkpointing: false
+    converter_type: "Qwen2ForCausalLM"
+    tensor_model_parallel_size: 1
+    expert_tensor_parallel_size: 1
+    expert_model_parallel_size: 1
+    pipeline_model_parallel_size: 1
+    num_layers_in_first_pipeline_stage: null
+    num_layers_in_last_pipeline_stage: null
+    context_parallel_size: 1
+    pipeline_dtype: ${policy.precision}
+    sequence_parallel: false
+    freeze_moe_router: true
+    moe_router_dtype: "fp64"
+    moe_router_load_balancing_type: "none" # "seq_aux_loss" causes logprob error divergence for grpo
+    moe_router_bias_update_rate: 0.0 # by default, disable bias updates for grpo
+    moe_permute_fusion: false
+    #gives ~20% training perf speedup with sequence packing
+    apply_rope_fusion: True
+    # gives ~25% training perf speedup with sequence packing and apply_rope_fusion
+    bias_activation_fusion: True
+    defer_fp32_logits: False
+
+    optimizer:
+      optimizer: "adam"
+      lr: 5.0e-6
+      min_lr: 5.0e-7
+      weight_decay: 0.01
+      bf16: true
+      fp16: false
+      params_dtype: "float32"
+
+      #adam
+      adam_beta1: 0.9
+      adam_beta2: 0.999
+      adam_eps: 1e-8
+
+      #sgd
+      sgd_momentum: 0.9
+
+      #distributed optimizer
+      use_distributed_optimizer: true
+      use_precision_aware_optimizer: true
+
+      clip_grad: ${policy.max_grad_norm}
+
+      # optimizer cpu offload
+      optimizer_cpu_offload: false
+      optimizer_offload_fraction: 0.0
+
+    scheduler:
+      start_weight_decay: ${policy.megatron_cfg.optimizer.weight_decay}
+      end_weight_decay: ${policy.megatron_cfg.optimizer.weight_decay}
+      weight_decay_incr_style: "constant"
+      lr_decay_style: "constant"
+      lr_decay_iters: 1000
+      lr_warmup_iters: 13
+      lr_warmup_init: 5.0e-7
+
+    distributed_data_parallel_config:
+      grad_reduce_in_fp32: false
+      overlap_grad_reduce: true
+      overlap_param_gather: true
+      use_custom_fsdp: false
+      data_parallel_sharding_strategy: "optim_grads_params"
+
+    fp8_cfg: null
+
+    env_vars: null
+
+  # See docs/design-docs/sequence-packing-and-dynamic-batching.md 
+  # for more details on dynamic batching and sequence packing.
+  dynamic_batching:
+    enabled: False
+    train_mb_tokens: ${mul:${policy.max_total_sequence_length}, ${policy.train_micro_batch_size}}
+    logprob_mb_tokens: ${mul:${policy.max_total_sequence_length}, ${policy.logprob_batch_size}}
+    sequence_length_round: 64
+
+  sequence_packing:
+    enabled: True
+    train_mb_tokens: ${mul:${policy.max_total_sequence_length}, ${policy.train_micro_batch_size}}
+    logprob_mb_tokens: ${mul:${policy.max_total_sequence_length}, ${policy.logprob_batch_size}}
+    algorithm: "modified_first_fit_decreasing"
+    sequence_length_round: 64
+
+  # makes the training sequence length divisible by the tensor parallel size
+  # this is useful for sequence parallel training
+  make_sequence_length_divisible_by: ${policy.dtensor_cfg.tensor_parallel_size}
+  max_grad_norm: 1.0
+
+  optimizer:
+    name: "torch.optim.AdamW"
+    kwargs:
+      lr: 5.0e-6
+      weight_decay: 0.01
+      betas: [0.9, 0.999]
+      eps: 1e-8
+      # when using Dtensor, we need to set foreach
+      # and fused to False
+      foreach: False
+      fused: False
+
+  scheduler:
+    - name: "torch.optim.lr_scheduler.LinearLR"
+      kwargs:
+        start_factor: 0.1
+        end_factor: 1.0
+        total_iters: 50
+    - name: "torch.optim.lr_scheduler.ConstantLR"
+      kwargs:
+        factor: 1.0
+        total_iters: 10000000000
+    - milestones: [50]
+
+  generation:
+    backend: "sglang"
+    max_new_tokens: ${policy.max_total_sequence_length}
+    temperature: 1.0
+    top_p: 1.0
+    top_k: null
+    stop_token_ids: null
+    stop_strings: null
+    sglang_cfg:
+      # SGLang specific configuration
+      model_path: ${policy.model_name} 
+      gpus_per_server: 1 
+      dtype: ${policy.precision}
+      context_length: 512  # Maximum context length
+      allow_auto_truncate: true
+      enable_memory_saver: false
+      max_running_requests: null
+      mem_fraction_static: 0.7
+      skip_server_warmup: true
+    colocated:
+      # true: generation shares training GPUs
+      # false: uses dedicated generation resources
+      enabled: true
+      # only relevant when enabled is false
+      resources:
+        gpus_per_node: null # Decides num gpus to be dedicated to generation when there is one node in the cluster i.e cluster.num_nodes == 1
+        num_nodes: null # Decides number of nodes to be dedicated to generation
+
+data:
+  max_input_seq_length: ${policy.max_total_sequence_length} # upper bound, real truncation occurs at vllm.max_model_len
+  prompt_file: "examples/prompts/cot.txt"
+  system_prompt_file: null
+  shuffle: true
+  num_workers: 1
+
+  dataset_name: "OpenMathInstruct-2"
+  # You can use custom response datasets for training and validation. For example:
+  #   data:
+  #     dataset_name: ResponseDataset
+  #     train_data_path: <PathToTrainingDataset>  # e.g., /path/to/local/dataset.jsonl or hf_org/hf_dataset_name (HuggingFace)
+  #     val_data_path: <PathToValidationDataset>
+  #     input_key: <QuestionKey>, default is "input"
+  #     output_key: <AnswerKey>, default is "output"
+  #     train_split: <TrainSplit>, default is None  # used for HuggingFace datasets
+  #     val_split: <ValSplit>, default is None  # used for HuggingFace datasets
+  # See https://github.com/NVIDIA-NeMo/RL/blob/main/docs/guides/grpo.md#datasets for more details.
+
+env:
+  math:
+    num_workers: 8
+    math_verify_impl: "hf_math_verify"
+  ## unused in this config but needed for DAPO recipe
+  dapo:
+    num_workers: 8
+    math_verify_impl: "dapo_math_verify"
+
+logger:
+  log_dir: "logs"  # Base directory for all logs
+  num_val_samples_to_print: 0 # Number of validation samples to pretty print on terminal
+  wandb_enabled: true
+  tensorboard_enabled: false
+  mlflow_enabled: false  # Disable MLflow logging
+  swanlab_enabled: false # Disable SwanLab logging
+  monitor_gpus: true  # If true, will monitor GPU usage and log to wandb and/or tensorboard
+  wandb:
+    project: "grpo-dev"
+    name: "grpo-dev-logger"
+  tensorboard: {}
+  mlflow:
+    experiment_name: "grpo-dev"
+    run_name: "grpo-dev-logger"
+  gpu_monitoring:
+    collection_interval: 10  # How often to collect GPU usage metrics (in seconds)
+    flush_interval: 10  # How often to flush GPU usage metrics to the loggers (in seconds)
+
+cluster:
+  gpus_per_node: 1
+  num_nodes: 1