Fusilli Benchmark Tests Fail With Multiple CTest Jobs Troubleshooting And Solutions

Experiencing failures in your Fusilli benchmark tests when running multiple ctest jobs? You're not alone! This article dives into a common issue encountered when utilizing parallel testing in the shark-ai/sharkfuser environment. We'll break down the problem, explore the root cause, and provide a practical solution to get your benchmarks running smoothly.

Understanding the Issue: Non-Deterministic Failures

Fusilli benchmark tests are crucial for evaluating the performance of your system. However, when you leverage the power of parallel testing using ctest -j <number_of_jobs>, you might encounter frustrating non-deterministic failures. These failures are often characterized by inconsistent error messages, making it challenging to pinpoint the exact problem. For instance, you might see errors like:

Fusilli Benchmark failed: RUNTIME_FAILURE: iree/runtime/src/iree/modules/hal/utils/buffer_diagnostics.c:208: INVALID_ARGUMENT; tensor shape rank mismatch; expected 4 but have 5; expected shape `48x3x3x48`, actual shape `288x2x1x1x288`; while invoking native function hal.buffer_view.assert; while calling import;

These errors can seem cryptic, but the key takeaway is that they don't consistently appear, suggesting an underlying concurrency issue rather than a fundamental code problem. This inconsistency can be a real headache, slowing down your development process and making it difficult to trust your benchmark results.

The Root Cause: Cache Contention

So, what's causing these Fusilli benchmark failures? The culprit lies in how the benchmark tests handle caching. All the tests, by default, attempt to use the same graph name (benchmark_conv_fprop), which translates to accessing the same cache directory: /tmp/.cache/fusilli/benchmark_conv_fprop. When multiple ctest jobs run concurrently, they all try to read from and write to this same directory. This leads to a cache contention problem, where multiple processes are fighting for access to the same resources, resulting in race conditions and ultimately, test failures.

Think of it like this: imagine multiple chefs trying to use the same cutting board at the same time. Chaos ensues! Similarly, when multiple tests try to access the same cache directory simultaneously, data corruption and unexpected behavior can occur.

Beyond the immediate test failures, this situation also raises a broader concern: multiple users on the same machine running tests could potentially interfere with each other due to the shared /tmp directory. This highlights the need for a more robust and isolated caching mechanism.

The Solution: Unique Cache Directories

Fortunately, there's a straightforward solution to this problem: prevent tests from overwriting pre-existing cache directories. Instead of using the same default directory, each test should attempt to create a unique cache directory. One effective approach is to append a unique identifier, such as a timestamp or a random number, to the directory name. For example, instead of /tmp/.cache/fusilli/benchmark_conv_fprop, the tests could use directories like /tmp/.cache/fusilli/benchmark_conv_fprop_<unique_number>. This ensures that each test has its own isolated workspace, eliminating the possibility of cache contention.

This approach not only resolves the immediate issue of non-deterministic failures but also enhances the overall robustness and reliability of your benchmark testing process. By isolating the cache directories, you create a more predictable and controlled environment, leading to more trustworthy results.

Implementing the Solution: A Practical Approach

To implement this solution, you'll need to modify the code that handles cache directory creation within your Fusilli benchmark tests. Here's a general outline of the steps involved:

1. Locate the cache directory creation logic: Identify the code responsible for creating the cache directory (e.g., /tmp/.cache/fusilli/benchmark_conv_fprop).
2. Generate a unique identifier: Implement a mechanism to generate a unique identifier. This could involve using a timestamp, a random number, or a process ID.
3. Append the identifier to the directory name: Modify the code to append the generated identifier to the base cache directory name.
4. Attempt to create the unique directory: Use appropriate file system functions (e.g., mkdir) to create the unique cache directory. Ensure that the code handles potential errors, such as the directory already existing.
5. Utilize the unique directory in the tests: Update the tests to use the newly created unique cache directory for storing and retrieving cached data.

By following these steps, you can effectively isolate the cache directories for each test, eliminating the risk of contention and ensuring the reliability of your benchmark results. This proactive approach will save you time and frustration in the long run.

Reproducing the Issue: A Simple Test

To demonstrate the problem and verify the solution, you can use the following steps to reproduce the issue within the shark-ai/sharkfuser environment:

1. Navigate to the shark-ai/sharkfuser directory: Open your terminal and navigate to the root directory of your shark-ai/sharkfuser project.

2. Execute the ctest command with multiple jobs: Run the following command to execute the tests using multiple jobs:

   ctest --test-dir build/ --output-on-failure -j 20
   

   This command instructs ctest to run the tests in the build/ directory, display output on failure, and use 20 parallel jobs. The -j 20 option is crucial for triggering the concurrency issue.

3. Observe the failures: If the issue is present, you should observe non-deterministic failures similar to the example error message provided earlier. The specific errors might vary, but the inconsistency is the key indicator.

By following these steps, you can confirm that you're experiencing the cache contention problem. After implementing the solution of using unique cache directories, repeat these steps to verify that the failures are resolved.

Broader Implications: Multi-User Environments

The Fusilli benchmark cache contention issue extends beyond single-user scenarios. In multi-user environments, where multiple users might be running tests on the same machine, the risk of cache collisions is even higher. Since /tmp is a shared directory, different users' tests could interfere with each other, leading to unpredictable results and potentially corrupted caches.

This underscores the importance of adopting robust caching strategies that provide isolation and prevent interference between different users and processes. Using unique cache directories is a critical step in this direction. Additionally, consider exploring other caching mechanisms, such as user-specific cache directories or dedicated cache servers, to further enhance isolation and performance in multi-user environments.

By addressing the cache contention issue, you not only improve the reliability of your benchmark tests but also create a more sustainable and scalable testing infrastructure for collaborative development environments. This proactive approach ensures that your benchmark results are accurate and trustworthy, regardless of the number of users or the complexity of your testing setup.

Conclusion: Ensuring Reliable Benchmarks

The non-deterministic failures encountered in Fusilli benchmark tests when using multiple ctest jobs highlight the importance of careful resource management in parallel testing environments. The root cause, cache contention, can be effectively addressed by using unique cache directories for each test run.

By implementing this solution, you'll not only resolve the immediate issue of inconsistent failures but also enhance the overall robustness and reliability of your benchmark testing process. This will lead to more trustworthy results, faster development cycles, and a more confident understanding of your system's performance.

Remember, thorough testing is crucial for building high-quality software. By addressing potential concurrency issues like cache contention, you're taking a significant step towards ensuring the accuracy and reliability of your benchmark results. So go ahead, implement unique cache directories, and unleash the full power of parallel testing with confidence!