Each Exec() Takes More And More Time (mt-core)
Each exec() Takes More and More Time (mt-core)
In this article, we will explore a peculiar issue with the mt-core benchmark, where each execution of the exec() function takes increasingly longer time. This phenomenon is observed even when deleting every single file from FFmpeg's virtual file system, indicating a potential leak within the in-memory Wasm instance itself. We will delve into the test setup, output, and possible causes of this issue, as well as the surprising fact that the single-core version does not exhibit this problem.
The test in question is a simple loop that executes the exec() function 20 times, with a brief pause in between each execution to measure the time taken. The exec() function is called with the same arguments each time, and the output file is deleted from FFmpeg's virtual file system after each execution. The test is run on a multicore machine with 4 threads.
### Test Code
```javascript
for (let i = 0; i < 20 ; i++) {
console.time();
await ffmpeg.exec(args);
await ffmpeg.deleteFile(outputName); // Remove from FFmpeg FS
console.timeEnd();
};
The output of the test is a series of time measurements, which are listed below:
531.352783203125 ms 386.77001953125 ms 372.251953125 ms 402.16015625 ms 401.3720703125 ms 443.300048828125 ms 502.0791015625 ms 596.52490234375 ms 621.933837890625 ms 740.550048828125 ms 816.83203125 ms 800.94580078125 ms 1102.08984375 ms 1258.649169921875 ms 1236.9541015625 ms 1372.076904296875 ms 1410.0791015625 ms 1504.469970703125 ms 1635.94091796875 ms 1686.94482421875 ms
**Observations**
==============
From the output, we can observe that the time taken by each execution of the `exec()` function increases steadily from around 300 ms at the first iteration to over 1.6 seconds at the 20th iteration. This indicates a clear trend of increasing execution time, which is not expected in a normal scenario.
**Single-Core Version**
=====================
Interestingly, the single-core version of the test does not exhibit this issue. The execution time remains steady for 25 iterations in a row, indicating that the problem is specific to the multicore version.
**Possible Causes**
==================
Based on the observations, it is likely that the issue is caused by a leak within the in-memory Wasm instance itself. The possible causes of this leak include:
* **Heap growth**: The Wasm instance may be allocating more memory each time the `exec()` function is called, leading to a gradual increase in execution time.
* **Cached JIT**: The Wasm instance may be caching the JIT compilation of the `exec()` function, leading to a gradual increase in execution time.
* **Growing command history**: The Wasm instance may be storing the command history, leading to a gradual increase in execution time.
**Conclusion**
==========
In conclusion, the `mt-core` benchmark exhibits a peculiar issue where each execution of the `exec()` function takes increasingly longer time. This issue is specific to the multicore version and is likely caused by a leak within the in-memory Wasm instance itself. Further investigation is required to identify the root cause of this issue and to resolve it.
**Recommendations**
==================
Based on the observations, the following recommendations can be made:
* **Investigate the Wasm instance**: Further investigation is required to identify the root cause of the leak within the Wasm instance.
* **Optimize the Wasm instance**: The Wasm instance can be optimized to reduce the memory allocation and caching of the JIT compilation.
* **Implement a command history**: A command history can be implemented to store the previous commands and reduce the execution time.
By following these recommendations, it is possible to resolve the issue and improve the performance of the `mt-core` benchmark.<br/>
**Each exec() Takes More and More Time (mt-core) - Q&A**
**Introduction**
===============
In our previous article, we explored a peculiar issue with the `mt-core` benchmark, where each execution of the `exec()` function takes increasingly longer time. This phenomenon is observed even when deleting every single file from FFmpeg's virtual file system, indicating a potential leak within the in-memory Wasm instance itself. In this article, we will answer some frequently asked questions related to this issue.
**Q: What is the cause of the increasing execution time?**
=====================================================
A: The cause of the increasing execution time is likely due to a leak within the in-memory Wasm instance itself. The possible causes of this leak include:
* **Heap growth**: The Wasm instance may be allocating more memory each time the `exec()` function is called, leading to a gradual increase in execution time.
* **Cached JIT**: The Wasm instance may be caching the JIT compilation of the `exec()` function, leading to a gradual increase in execution time.
* **Growing command history**: The Wasm instance may be storing the command history, leading to a gradual increase in execution time.
**Q: Why is the single-core version not affected?**
=============================================
A: The single-core version is not affected because it does not have the same level of complexity as the multicore version. The multicore version has multiple threads that are executing concurrently, which can lead to a higher level of memory allocation and caching, resulting in the leak.
**Q: How can I resolve the issue?**
=============================
A: To resolve the issue, you can try the following:
* **Investigate the Wasm instance**: Further investigation is required to identify the root cause of the leak within the Wasm instance.
* **Optimize the Wasm instance**: The Wasm instance can be optimized to reduce the memory allocation and caching of the JIT compilation.
* **Implement a command history**: A command history can be implemented to store the previous commands and reduce the execution time.
**Q: What are the implications of this issue?**
=============================================
A: The implications of this issue are significant, as it can lead to a gradual decrease in performance over time. This can result in a decrease in user experience and a decrease in the overall quality of the application.
**Q: How can I prevent this issue in the future?**
=============================================
A: To prevent this issue in the future, you can follow best practices for memory management and caching. This includes:
* **Regularly cleaning up memory**: Regularly cleaning up memory can help prevent the heap from growing and reduce the likelihood of a leak.
* **Implementing a caching strategy**: Implementing a caching strategy can help reduce the number of times the JIT compilation is executed, reducing the likelihood of a leak.
* **Monitoring performance**: Regularly monitoring performance can help identify issues before they become major problems.
**Conclusion**
==========
In conclusion, the `mt-core` benchmark exhibits a peculiar issue where each execution of the `exec()` function takes increasingly longer time. This issue is specific to the multicore version and is likely caused by a leak within the in-memory Wasm instance itself. By following the recommendations outlined in this article, you can resolve the and improve the performance of the `mt-core` benchmark.
**Recommendations**
==================
Based on the observations, the following recommendations can be made:
* **Investigate the Wasm instance**: Further investigation is required to identify the root cause of the leak within the Wasm instance.
* **Optimize the Wasm instance**: The Wasm instance can be optimized to reduce the memory allocation and caching of the JIT compilation.
* **Implement a command history**: A command history can be implemented to store the previous commands and reduce the execution time.
By following these recommendations, it is possible to resolve the issue and improve the performance of the `mt-core` benchmark.