fix(tests): Ensure reliable CUDA cache clearing in MoE test

[AzizCode92]

In test_mixtral_moe, torch.cuda.empty_cache() is called immediately after an F.pad operation.

Due to the asynchronous nature of CUDA kernels, there's no guarantee that the padding operation has completed on the GPU before the cache is cleared. This can make the empty_cache() call ineffective.

This commit adds torch.cuda.synchronize() before torch.cuda.empty_cache() to ensure all pending GPU work is finished, making memory management in the test more reliable and deterministic.

Purpose

This PR improves the reliability of memory management in the test_mixtral_moe test by addressing a potential race condition between the CPU and GPU.

Currently, torch.cuda.empty_cache() is called immediately after an asynchronous CUDA operation (F.pad). There is no guarantee that the GPU has finished the operation before the cache-clearing command is issued, which can render empty_cache() ineffective.

This change introduces a torch.cuda.synchronize() call before empty_cache() to ensure all pending GPU kernels are complete, making the test's memory handling more robust and deterministic.

Test Plan

pytest tests/kernels/test_moe.py -k test_mixtral_moe

Test Result

(Optional) Documentation Update

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

[gemini-code-assist]

Code Review

This pull request correctly addresses a potential race condition in the test_mixtral_moe test by adding torch.cuda.synchronize() before torch.cuda.empty_cache(). This ensures that asynchronous CUDA operations complete before attempting to clear the cache, making the test more reliable. I have one suggestion to further improve the efficiency by reducing the number of synchronization points.

[github-actions]

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[mgoin]

Thanks for the find! Although I haven't seen this test flaky before, it makes sense.