significant delays when using many devices

Oct 13, 2025 by pinkandtrash.com 117 views

Issue Description

When training with multiple devices using Fabric, the generate_example() function is redundantly called on every GPU/rank, leading to inefficient resource utilization. Each rank performs the identical computation while only the output from rank 0 is actually displayed through fabric.print(). This causes significant delays when using many devices.

The issue arises from the fact that each rank is independently generating examples, resulting in multiple redundant calls to generate_example(). This not only wastes GPU resources but also slows down the training process.

Reproduction Steps

To reproduce this issue, follow these steps:

Run a finetuning job using multiple GPUs (in my case, 8 GPUs).
Observe the logs, which will show each rank independently generating examples.

Evidence

The logs will display multiple "[Rank N] Generating example..." messages followed by each rank performing the same operations:

Rank 0 validating...
Rank 0 completed validation in 56.52 seconds
Rank 0 generating example...

Rank 2 validating...
Rank 2 completed validation in 56.43 seconds
Rank 2 generating example...

Rank 3 validating...
Rank 3 completed validation in 56.44 seconds
Rank 3 generating example...

Rank 4 validating...
Rank 4 completed validation in 56.47 seconds
Rank 4 generating example...

Expected Behavior

The expected behavior is that only rank 0 should generate the example, or the work should be properly distributed across devices with results gathered at rank 0. This would prevent the redundant calls to generate_example() and ensure efficient resource utilization.

Suggested Fix

To fix this issue, modify the code to only call generate_example() on rank 0, or implement proper distribution of this workload:

if fabric.global_rank == 0:
    generate_example(fabric, model, tokenizer, eval, data)
fabric.barrier()

This change will ensure that only rank 0 generates the example, preventing redundant calls and improving resource utilization.

Additional Information

Operating System

The operating system used is Linux.

LitGPT Version

The version of LitGPT used is 0.5.8.dev1.

Conclusion

The issue of multiple redundant calls to generate_example() when using multiple GPUs is a significant problem that can cause delays and waste GPU resources. By modifying the code to only call generate_example() on rank 0 or implementing proper distribution of this workload, we can prevent redundant calls and improve resource utilization. This change will ensure efficient training with multiple devices and improve overall performance.

Code Implementation

The code implementation for this fix is as follows:

if fabric.global_rank == 0:
    generate_example(fabric, model, tokenizer, eval, data)
fabric.barrier()

This code will only call generate_example() on rank 0, preventing redundant calls and improving resource utilization.

Benefits of the Fix

The benefits of this fix include:

Improved resource utilization: By preventing redundant calls to generate_example(), we can improve resource utilization and reduce waste.
Faster training: By reducing the number of redundant calls, we can improve the overall training speed.
Improved performance: By improving resource utilization and reducing redundant calls, we can improve the overall performance of the training process.

Future Work

Future work on this issue could include:

Implementing proper distribution of the workload across devices.
Improving the code to handle multiple GPUs more efficiently.
Testing the fix on different operating systems and LitGPT versions.

Conclusion

In conclusion, the issue of multiple redundant calls to generate_example() when using multiple GPUs is a significant problem that can cause delays and waste GPU resources. By modifying the code to only call generate_example() on rank 0 or implementing proper distribution of this workload, we can prevent redundant calls and improve resource utilization. This change will ensure efficient training with multiple devices and improve overall performance.

Q: What is the issue with `generate_example()` when using multiple GPUs?

A: The issue is that generate_example() is redundantly called on every GPU/rank, leading to inefficient resource utilization. Each rank performs the identical computation while only the output from rank 0 is actually displayed through fabric.print().

Q: Why is this a problem?

A: This causes significant delays when using many devices. The redundant calls to generate_example() waste GPU resources and slow down the training process.

Q: How can I reproduce this issue?

A: To reproduce this issue, follow these steps:

Run a finetuning job using multiple GPUs (in my case, 8 GPUs).
Observe the logs, which will show each rank independently generating examples.

Q: What does the evidence show?

A: The logs will display multiple "[Rank N] Generating example..." messages followed by each rank performing the same operations:

Rank 0 validating...
Rank 0 completed validation in 56.52 seconds
Rank 0 generating example...

Rank 2 validating...
Rank 2 completed validation in 56.43 seconds
Rank 2 generating example...

Rank 3 validating...
Rank 3 completed validation in 56.44 seconds
Rank 3 generating example...

Rank 4 validating...
Rank 4 completed validation in 56.47 seconds
Rank 4 generating example...

Q: What is the expected behavior?

A: The expected behavior is that only rank 0 should generate the example, or the work should be properly distributed across devices with results gathered at rank 0.

Q: How can I fix this issue?

A: To fix this issue, modify the code to only call generate_example() on rank 0, or implement proper distribution of this workload:

if fabric.global_rank == 0:
    generate_example(fabric, model, tokenizer, eval, data)
fabric.barrier()

Q: What are the benefits of this fix?

A: The benefits of this fix include:

Improved resource utilization: By preventing redundant calls to generate_example(), we can improve resource utilization and reduce waste.
Faster training: By reducing the number of redundant calls, we can improve the overall training speed.
Improved performance: By improving resource utilization and reducing redundant calls, we can improve the overall performance of the training process.

Q: What are some potential future work on this issue?

A: Some potential future work on this issue could include:

Implementing proper distribution of the workload across devices.
Improving the code to handle multiple GPUs more efficiently.
Testing the fix on different operating systems and LitGPT versions.

Q: What is the LitGPT version used in this issue?

A: The version of LitGPT used is 0.5.8.dev1.

Q: What is the operating system used in this issue?

A: The operating system used is Linux.

Q: How can I get help with this issue?

A: If you are experiencing this issue, you can try the following:

Check the LitGPT documentation for more information on using multiple GPUs.
Search online for solutions to similar issues.
Reach out to the LitGPT community for help and support.

Q: What are some common mistakes to avoid when using multiple GPUs?

A: Some common mistakes to avoid when using multiple GPUs include:

Not properly configuring the GPU settings.
Not using the correct version of LitGPT.
Not following the recommended guidelines for using multiple GPUs.

Q: How can I optimize my code for multiple GPUs?

A: To optimize your code for multiple GPUs, you can try the following:

Use the fabric library to handle multiple GPUs.
Use the torch library to handle GPU operations.
Use the torch.distributed library to handle distributed training.

Q: What are some best practices for using multiple GPUs?

A: Some best practices for using multiple GPUs include:

Using the correct version of LitGPT.
Following the recommended guidelines for using multiple GPUs.
Testing your code on a single GPU before moving to multiple GPUs.

Q: How can I troubleshoot issues with multiple GPUs?

A: To troubleshoot issues with multiple GPUs, you can try the following:

Check the LitGPT documentation for more information on using multiple GPUs.
Search online for solutions to similar issues.
Reach out to the LitGPT community for help and support.