关于qwen1.5长序列训练的疑问

[macheng6]

使用A100-32卡，xtuner训练qwen1.5-32b长序列，有下面几个疑问想请教一下：

1. qwen1.5貌似不支持use_varlen_attn=True参数，这个功能后面有计划增加吗？
2. 对于特定模型来说，use_varlen_attn=True与use_varlen_attn=False，是否有明显差别？
3. 在scheduler设置为按照step更新时，有没有公式可以计算总共需要训练多少个steps？然后好设置begin和end?
4. 在多机多卡训练时，一条pack到max_length的数据，是怎么根据sequence_parallel_size与总卡数来切分数据的？

[HIT-cwh]

1. qwen1.5 目前支持设置 use_varlen_attn=True
2. varlen 是 True or False 决定了attn计算的时候是只在每条短数据内算attn，还是在整条max_length长度的长数据内算loss。如果训练数据集数据长度普遍较短，且相互之间没什么关联，模型训练难度会增大，但也可以理解成是一种数据增强。
3. XTuner 提供的 config 都是按照step更新lr的。例如，这个 qwen1_5_0_5b_chat_full_alpaca_e3.py config 中的学习率就是1. 前 3%的iter是warmup ，后面97%的iters是cos下降
4. 一条数据会被切分为 sequence_parallel_size 份，因此sp_size = world_size // dp_size

[macheng6]

感谢回答，还有疑问是：

1. use_varlen_attn=True时，报错如下：
   File "/opt/conda/lib/python3.8/site-packages/transformers/models/qwen2/modeling_qwen2.py", line 748, in forward
   hidden_states, self_attn_weights, present_key_value = self.self_attn(
   File "/opt/conda/lib/python3.8/site-packages/torch/nn/modules/module.py", line 1538, in _call_impl
   result = forward_call(*args, **kwargs)
   File "/nas/macheng.ma/projects/xtuner-main/xtuner/model/modules/dispatch/qwen2.py", line 317, in qwen2_varlen_attn_forward
   attn_output = varlen_flash_attn(attn_output = varlen_flash_attn(

   File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/attention.py", line 65, in sequence_parallel_attn
   attn_output = varlen_flash_attn( File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/attention.py", line 65, in sequence_parallel_attn

File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/attention.py", line 65, in sequence_parallel_attn
pre_process_for_sequence_parallel_attn(pre_process_for_sequence_parallel_attn(

File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/attention.py", line 23, in pre_process_for_sequence_parallel_attn
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/attention.py", line 23, in pre_process_for_sequence_parallel_attn
pre_process_for_sequence_parallel_attn(
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/attention.py", line 23, in pre_process_for_sequence_parallel_attn
query_states = all_to_all(
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 87, in all_to_all
query_states = all_to_all(
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 87, in all_to_all
query_states = all_to_all(
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 87, in all_to_all
return _AllToAll.apply(input, sp_group, scatter_dim, gather_dim)
File "/opt/conda/lib/python3.8/site-packages/torch/autograd/function.py", line 506, in apply
return _AllToAll.apply(input, sp_group, scatter_dim, gather_dim)
File "/opt/conda/lib/python3.8/site-packages/torch/autograd/function.py", line 506, in apply
return _AllToAll.apply(input, sp_group, scatter_dim, gather_dim)
File "/opt/conda/lib/python3.8/site-packages/torch/autograd/function.py", line 506, in apply
return super().apply(*args, **kwargs) # type: ignore[misc]
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 42, in forward
return super().apply(*args, **kwargs) # type: ignore[misc]
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 42, in forward
return super().apply(*args, **kwargs) # type: ignore[misc]
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 42, in forward
output = _all_to_all(input, ctx.world_size, sp_group, scatter_dim,
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 21, in _all_to_all
output = _all_to_all(input, ctx.world_size, sp_group, scatter_dim,
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 21, in _all_to_all
output = _all_to_all(input, ctx.world_size, sp_group, scatter_dim,
File "/nas/macheng.ma/projects/xtuner-main/xtuner/parallel/sequence/comm.py", line 21, in _all_to_all
dist.all_to_all(output_list, input_list, group=group)
File "/opt/conda/lib/python3.8/site-packages/torch/distributed/distributed_c10d.py", line 1436, in wrapper
dist.all_to_all(output_list, input_list, group=group)
File "/opt/conda/lib/python3.8/site-packages/torch/distributed/distributed_c10d.py", line 1436, in wrapper
dist.all_to_all(output_list, input_list, group=group)
File "/opt/conda/lib/python3.8/site-packages/torch/distributed/distributed_c10d.py", line 1441, in wrapper
return func(*args, **kwargs)
File "/opt/conda/lib/python3.8/site-packages/torch/distributed/distributed_c10d.py", line 3266, in all_to_all
"args": f"{args}, {kwargs}",return func(*args, **kwargs)

File "/opt/conda/lib/python3.8/site-packages/torch/_tensor.py", line 426, in repr
File "/opt/conda/lib/python3.8/site-packages/torch/distributed/distributed_c10d.py", line 3266, in all_to_all
return torch._tensor_str._str(self, tensor_contents=tensor_contents)
File "/opt/conda/lib/python3.8/site-packages/torch/_tensor_str.py", line 636, in _str
work = group.alltoall(output_tensor_list, input_tensor_list, opts)
torch.distributed.DistBackendError: NCCL error in: ../torch/csrc/distributed/c10d/ProcessGroupNCCL.cpp:1275, internal error, NCCL version 2.14.3
ncclInternalError: Internal check failed.

2. qwen1_5_0_5b_chat_full_alpaca_e3.py这个文件中，by_epoch=True应该是按照epoch来更新学习率，并不是按照step？

[HIT-cwh]

1. 大概率是nccl的版本问题，请先检查bashrc里有没有自己设置nccl相关的环境变量。然后用 pip install 的方式装最近版本的 torch ，会自动装 nccl 依赖。
2. lr scheduler里有一个convert_to_iter_based=True的设置，我们会自动把begin, end中的epoch数转换为iter 数，学习率是按照step更新的。
   

[macheng6]

好的，感谢回答。