多卡跑会报错 单卡不会

Expected to have finished reduction in the prior iteration before starting a new one. This error indicates that your module has parameters that were not used in producing loss. You can enable unused parameter detection by passing the keyword argument `find_unused_parameters=True` to `torch.nn.parallel.DistributedDataParallel`, and by making sure all `forward` function outputs participate in calculating loss. 已经加了find_unused_parameters=True 还是报错

求大佬解决

可以在单卡时一次backward之后检查下模型参数的梯度，看下是否是哪些参数没梯度