question: Get batch’s datapoints across all GPUs
context: Hello,
  I´m running my model in a cluster with multiples GPUs (2). My problem is that I would like to access all the datapoints in the batch (predictions and labels). Because I´m using more than 2 GPUs, my batch in divided between those two devices for parallelisation purposes, which means than when I access the data in the batch in eval/training, I´m getting just half the batch.
  How could I obtain the complete batch and the predictions of the model that are divided among different devices/GPUs? @rohitgr7 suggested using self.all_gather, but after trying it on my LightningModule’s forward method, I get just half the batch, that is, just the data stored in one of the two GPUs being used.
  Thanks!
  PD:  may it be possible to access this info through "validation_epoch_end", "test_epoch_end", etc?
answer: if you are going to use the complete batch on the single GPU, then why use DDP?
  if you need predictions on a single device, you can rather gather all the predictions using all_gather.