verl/workers/sharding_manager/fsdp_sglang.py

# Copyright 2023-2024 SGLang Team
# Copyright 2025 ModelBest Inc. and/or its affiliates
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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#
#     http://www.apache.org/licenses/LICENSE-2.0
#
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# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# limitations under the License.
# ==============================================================================
# Copyright 2024 Bytedance Ltd. and/or its affiliates
#
# 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
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#     http://www.apache.org/licenses/LICENSE-2.0
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# 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.
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import logging
import os
from typing import Union

import torch
import torch.distributed as dist
from sglang.srt.entrypoints.engine import Engine
from sglang.srt.entrypoints.verl_engine import VerlEngine
from sglang.srt.model_executor.model_runner import LocalSerializedTensor
from sglang.srt.utils import MultiprocessingSerializer
from torch.distributed.device_mesh import DeviceMesh
from torch.distributed.fsdp.api import FullStateDictConfig, ShardedStateDictConfig, StateDictType
from torch.distributed.fsdp.fully_sharded_data_parallel import FullyShardedDataParallel as FSDP
from torch.distributed.tensor import DTensor

from verl import DataProto
from verl.protocol import all_gather_data_proto
from verl.utils.debug import log_gpu_memory_usage
from verl.utils.fsdp_utils import fsdp_version, load_fsdp_model_to_gpu, offload_fsdp_model_to_cpu
from verl.utils.torch_functional import broadcast_dict_tensor, check_cuda_is_available

from .base import BaseShardingManager

# from vllm.distributed import parallel_state as sglang_ps
logger = logging.getLogger(__file__)
logger.setLevel(os.getenv("VERL_LOGGING_LEVEL", "WARN"))


def _preprocess_tensor_for_update_weights(tensor: torch.Tensor):
    if isinstance(tensor, DTensor):
        return tensor.full_tensor()
    return tensor


class FSDPSGLangShardingManager(BaseShardingManager):
    @check_cuda_is_available()
    def __init__(
        self,
        module: FSDP,
        inference_engine: Union[VerlEngine, Engine],
        model_config,
        full_params: bool = False,
        device_mesh: DeviceMesh = None,
        offload_param: bool = False,
    ):
        self.module = module
        self.inference_engine = inference_engine
        self.model_config = model_config
        self.device_mesh = device_mesh
        self.offload_param = offload_param

        # Full params
        self.full_params = full_params
        if full_params and fsdp_version(self.module) == 1:
            FSDP.set_state_dict_type(self.module, state_dict_type=StateDictType.FULL_STATE_DICT, state_dict_config=FullStateDictConfig())
        elif fsdp_version(self.module) == 1:
            FSDP.set_state_dict_type(
                self.module,
                state_dict_type=StateDictType.SHARDED_STATE_DICT,
                state_dict_config=ShardedStateDictConfig(),
            )

        # Note that torch_random_states may be different on each dp rank
        self.torch_random_states = torch.cuda.get_rng_state()
        # get a random rng states
        if self.device_mesh is not None:
            gen_dp_rank = self.device_mesh["dp"].get_local_rank()
            torch.cuda.manual_seed(gen_dp_rank + 1000)  # make sure all tp ranks have the same random states
            self.gen_random_states = torch.cuda.get_rng_state()
            torch.cuda.set_rng_state(self.torch_random_states)
        else:
            self.gen_random_states = None

    def __enter__(self):
        torch.cuda.empty_cache()
        log_gpu_memory_usage("Before state_dict() in sharding manager memory", logger=logger)
        if self.offload_param:
            load_fsdp_model_to_gpu(self.module)
        params = self.module.state_dict()
        log_gpu_memory_usage("After state_dict() in sharding manager memory", logger=logger)
        device = torch.cuda.current_device()  # used when fsdp2 set cpu_offload_policy
        params = {k: v.to(device, non_blocking=True) if fsdp_version(self.module) == 2 else v for k, v in params.items()}
        # Copy, not share memory
        self.update_weights(params)
        log_gpu_memory_usage("After sync model weights in sharding manager", logger=logger)

        del params
        if self.offload_param:
            offload_fsdp_model_to_cpu(self.module)
        torch.cuda.empty_cache()
        log_gpu_memory_usage("After del state_dict and empty_cache in sharding manager", logger=logger)

        # important: need to manually set the random states of each tp to be identical.
        if self.device_mesh is not None:
            self.torch_random_states = torch.cuda.get_rng_state()
            torch.cuda.set_rng_state(self.gen_random_states)

    def __exit__(self, exc_type, exc_value, traceback):
        log_gpu_memory_usage("Before SGLang offload in sharding manager", logger=logger)
        self.release_memory()
        log_gpu_memory_usage("After SGLang offload in sharding manager", logger=logger)

        self.module.train()

        # add empty cache after each compute
        torch.cuda.empty_cache()

        # restore random states
        if self.device_mesh is not None:
            self.gen_random_states = torch.cuda.get_rng_state()
            torch.cuda.set_rng_state(self.torch_random_states)

    def update_weights(self, params):
        self.inference_engine.resume_memory_occupation()
        self.inference_engine.update_weights_from_tensor([(k, v) for k, v in params.items()], load_format=None)

    def release_memory(self):
        self.inference_engine.release_memory_occupation()

    def preprocess_data(self, data: DataProto) -> DataProto:
        """All gather across tp group to make each rank has identical input."""
        if self.device_mesh["infer_tp"].mesh.size()[0] == 1:
            return data

        # TODO: Current impl doesn't consider FSDP with torch micro-dp
        group = self.device_mesh["infer_tp"].get_group()

        all_gather_data_proto(data=data, process_group=group)
        return data

    def postprocess_data(self, data: DataProto) -> DataProto:
        # TODO: Current impl doesn't consider FSDP with torch micro-dp
        global_rank = self.device_mesh.get_rank()
        tp_rank = self.device_mesh["infer_tp"].get_local_rank()
        tp_size = self.device_mesh["infer_tp"].mesh.size()[0]
        src_rank = global_rank // tp_size * tp_size
        broadcast_dict_tensor(data.batch, src=src_rank, group=self.device_mesh["infer_tp"].get_group())
        if tp_size > 1:
            local_prompts = data.chunk(chunks=tp_size)
            data = local_prompts[tp_rank]
        return data


class FSDPAsyncSGLangShardingManager(FSDPSGLangShardingManager):
    def __init__(
        self,
        module: FSDP,
        inference_engine: Engine,
        model_config,
        full_params: bool = False,
        device_mesh: DeviceMesh = None,
        offload_param: bool = False,
    ):
        super().__init__(module, inference_engine, model_config, full_params, device_mesh, offload_param)

    def update_weights(self, params):
        load_format = None if self.full_params else "dtensor"
        if self.device_mesh["infer_tp"].get_local_rank() == 0:
            self.inference_engine.resume_memory_occupation()

        # Most naive implementation, can optimize a lot if it is bottleneck from sglang VerlEngine
        named_tensors = [(k, v) for k, v in params.items()]
        load_format = None
        for tensor_index, (name, tensor) in enumerate(named_tensors):
            serialized_tensor = MultiprocessingSerializer.serialize(_preprocess_tensor_for_update_weights(tensor))

            if self.device_mesh["infer_tp"].get_local_rank() == 0:
                gathered_serialized_tensors = [None for _ in range(self.device_mesh["infer_tp"].mesh.size()[0])]
            else:
                gathered_serialized_tensors = None
            dist.gather_object(
                obj=serialized_tensor,
                object_gather_list=gathered_serialized_tensors,
                dst=self.device_mesh["infer_tp"].mesh.tolist()[0],
                group=self.device_mesh["infer_tp"].get_group(),
            )

            if self.device_mesh["infer_tp"].get_local_rank() == 0:
                self.inference_engine.update_weights_from_tensor(
                    named_tensors=[
                        (
                            name,
                            LocalSerializedTensor(values=gathered_serialized_tensors),
                        )
                    ],
                    load_format=load_format,
                    flush_cache=tensor_index == len(named_tensors) - 1,
                )

    def release_memory(self):
        if self.device_mesh["infer_tp"].get_local_rank() == 0:
            self.inference_engine.release_memory_occupation()