validation_epoch_end behavior with DDP
I might be misunderstanding how PL works, but when using DDP my validation_epoch_end argument still contains batches from single GPUs, and I thought they would be collated from all GPUs.
E.g. My validation dataset has 888 images, but when I validate on 8 GPUs (batch size of 1), I only get 111 batches in validation_epoch_end.
If that's correct, how can I produce metrics that combine information from all GPUs?