Fastconformer-CTC crashing with Watchdog caught collective operation timeout
State: closed | Pull request: no
Labels: name: bug

name: stale

Hi,

We're trying to finetune the stt_en fastconformer_ctc large model on around 20k hours of data on 2 h100s. We're using 128 batch size and 8 num_workers and we trained the tokenizer with 1024 vocab_size. The training is taking very long, more than 30 hours per epoch and after around 70-80% of the first epoch it's crashing with the following error:

```
Epoch 0:  78%|█████████████████████████████████████████████████████████████▎                 | 64809/83556 [25:06:58<7:15:54,  1.40s/it, v_num=18][rank1]:[E ProcessGroupNCCL.cpp:563] [Rank 
1] Watchdog caught collective operation timeout: WorkNCCL(SeqNum=1363596, OpType=BROADCAST, NumelIn=5158880, NumelOut=5158880, Timeout(ms)=1800000) ran for 1800047 milliseconds before timin
g out.
[rank1]:[E ProcessGroupNCCL.cpp:1316] [PG 0 Rank 1] Heartbeat monitor timed out! Process will be terminated after dumping debug info. workMetaList_.size()=2
[rank1]:[E ProcessGroupNCCL.cpp:1153] [PG 0 Rank 1] ProcessGroupNCCL preparing to dump debug info.
[rank1]:[F ProcessGroupNCCL.cpp:1169] [PG 0 Rank 1] [PG 0 Rank 1] ProcessGroupNCCL's watchdog got stuck for 600 seconds without making progress in monitoring enqueued collectives. This typi
cally indicates a NCCL/CUDA API hang blocking the watchdog, and could be triggered by another thread holding the GIL inside a CUDA api, or other deadlock-prone behaviors.If you suspect the 
watchdog is not actually stuck and a longer timeout would help, you can either increase the timeout (TORCH_NCCL_HEARTBEAT_TIMEOUT_SEC) to a larger value or disable the heartbeat monitor (TO
RCH_NCCL_ENABLE_MONITORING=0).If either of aforementioned helps, feel free to file an issue to PyTorch about the short timeout or false positive abort; otherwise, please attempt to debug th
e hang. workMetaList_.size() = 2
[rank0]:[E ProcessGroupNCCL.cpp:563] [Rank 0] Watchdog caught collective operation timeout: WorkNCCL(SeqNum=1363598, OpType=ALLREDUCE, NumelIn=1, NumelOut=1, Timeout(ms)=1800000) ran for 18
00095 milliseconds before timing out.
[rank0]:[E ProcessGroupNCCL.cpp:1537] [PG 0 Rank 0] Timeout at NCCL work: 1363598, last enqueued NCCL work: 1363598, last completed NCCL work: 1363597.
[rank0]:[E ProcessGroupNCCL.cpp:577] [Rank 0] 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.
[rank0]:[E ProcessGroupNCCL.cpp:583] [Rank 0] To avoid data inconsistency, we are taking the entire process down.
[rank0]:[E ProcessGroupNCCL.cpp:1414] [PG 0 Rank 0] Process group watchdog thread terminated with exception: [Rank 0] Watchdog caught collective operation timeout: WorkNCCL(SeqNum=1363598, 
OpType=ALLREDUCE, NumelIn=1, NumelOut=1, Timeout(ms)=1800000) ran for 1800095 milliseconds before timing out.
Exception raised from checkTimeout at ../torch/csrc/distributed/c10d/ProcessGroupNCCL.cpp:565 (most recent call first):
frame #0: c10::Error::Error(c10::SourceLocation, std::string) + 0x57 (0x7f47fd81e897 in /anaconda/envs/nemo_hindi/lib/python3.10/site-packages/torch/lib/libc10.so)
frame #1: c10d::ProcessGroupNCCL::WorkNCCL::checkTimeout(std::optional<std::chrono::duration<long, std::ratio<1l, 1000l> > >) + 0x1d2 (0x7f47feaf7c62 in /anaconda/envs/nemo_hindi/lib/python
3.10/site-packages/torch/lib/libtorch_cuda.so)
frame #2: c10d::ProcessGroupNCCL::watchdogHandler() + 0x1a0 (0x7f47feafca80 in /anaconda/envs/nemo_hindi/lib/python3.10/site-packages/torch/lib/libtorch_cuda.so)
frame #3: c10d::ProcessGroupNCCL::ncclCommWatchdog() + 0x10c (0x7f47feafddcc in /anaconda/envs/nemo_hindi/lib/python3.10/site-packages/torch/lib/libtorch_cuda.so)
frame #4: <unknown function> + 0xdbbf4 (0x7f484a5a6bf4 in /anaconda/envs/nemo_hindi/bin/../lib/libstdc++.so.6)
frame #5: <unknown function> + 0x8609 (0x7f484ba9b609 in /lib/x86_64-linux-gnu/libpthread.so.0)
frame #6: clone + 0x43 (0x7f484b866353 in /lib/x86_64-linux-gnu/libc.so.6)

Aborted (core dumped)
```

How do we avoid this issue? Should we consider reducing the finetuning data size?  If we save intermediate checkpoints, is there a way to also save the lr scheduler state to effectively resume the training if it crashes? Any guidance regarding this would be of great help. 

Also, unrelated to the issue, we noticed we didn't get much boost by using h100 instead of a100, and sometimes using bf16-mixed was slower on h100 than using fp16 on h100, on the other hand, bf16-mixed is almost always faster on a100 than fp16, is this expected?

Thank you!

I have the same issue. Have you solved it? How can we avoid it？

First, to triage whether it's the model or data store as the problem, run with a subset of data, maybe 50 hours of so. What is the max duration of the data ? Reduce it to at most 40 seconds, preferably 30 sec. We have some tools to segment data automatically. 

Next, nccl timeout is hard to debug because NeMo code mostly uses pytorch, we don't do much at nccl level so it can be due to many different reasons. See if model fine-tuning on single gpu with small bs is working first then try two gpus. 

LR and optimizer State is preserved in the ckpt files saved by Lightning during training. If you use exp manager, resuming a job is quite easy, see the docs for exp manager and tutorials showcasing training with it (just run the same script again with same output dir if you have set the two resume flags in exp manager). 

We don't have much information about hardware effects on certain operation in our team, we rely on pytorch and pytorch lightning to provide stable training engine 

This issue is stale because it has been open for 30 days with no activity. Remove stale label or comment or this will be closed in 7 days.

It might be a memory leak, it happened sometime when the system RAM is
full.

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This issue is stale because it has been open for 30 days with no activity. Remove stale label or comment or this will be closed in 7 days.

This issue was closed because it has been inactive for 7 days since being marked as stale.