Training the canary model with the default sampler

[literate-goggles]

Hi, the current samplers used for the Lhotse datasets to train the canary encode-decoder model are DynamicBucketingSampler and DynamicCutSampler both don't implement the len method, so the training on the multiple gpus fails with the following error:

TypeError: You seem to have configured a sampler in your DataLoader which does not provide `__len__` method. The sampler was about to be replaced by `DistributedSamplerWrapper` since `use_distributed_sampler` is True and you are using distributed training. Either provide `__len__` method in your sampler, remove it from DataLoader or set `use_distributed_sampler=False` if you want to handle distributed sampling yourself.

Have you trained the canary model with the use_distributed_sampler=False settings? In this case, the training hangs up with the following CUDA error:

[rank1]:[E ProcessGroupNCCL.cpp:768] Some NCCL operations have failed or timed out. Due to the asynchronous
 nature of CUDA kernels, subsequent GPU operations might run on corrupted/incomplete data.

I guess it is because on some GPUs batches are excedded early.

What is the preferred approach in this case? Should I implement the len method on my own?

[titu1994]

Are you using Lhotse ? We trained Canary with it, and Lhotse is the default data backend for ASR going forward

Fyi @pzelasko in case you have any suggestions

[literate-goggles]

Yes, I'm using Lhotse, and it's the main problem because the samplers implemented for it don't work with the default examples/asr/conf/speech_multitask/fast-conformer_aed.yaml config due to the problems in the description.

[pzelasko]

Yes, we trained Canary with Lhotse dataloaders. Please check that you have specified all required PyTorch Lightning trainer flags as described in this example in the documentation https://docs.nvidia.com/nemo-framework/user-guide/latest/nemotoolkit/asr/datasets.html#enabling-lhotse-via-configuration

If that doesn't help, please share the config you're running it with.

[pzelasko]

Also, please post a full stack trace or ideally the full log.

[literate-goggles]

Thanks! The problem was that I didn't specify the ++trainer.limit_train_batches=1000 flags, which is kind of unusual that during the training we don't have the information of the actual batch count.

[pzelasko]

Yes, with dynamic batch sizes it is not viable to estimate the number of batches up front.