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## Summary of the article: This article explains how to use the `systemtap` tool to inject delays into the I/O system, simulating hardware I/O jitter to test its impact on an application experiencing performance issues. **Key points:** * `systemtap` is used to control the timing and duration of injected delays. * The target device can be controlled through the `ka_cnt` variable. * The script can be customized to specify the target device, delay duration, and other parameters. * The script generates an `ik.ko` binary that needs to be placed on the target machine. * The script needs to be compiled and run on the target machine with appropriate permissions. * Running the script starts an `inject` process that continuously writes "on" and "off" messages to a file, simulating I/O operations. **Benefits of using `systemtap`:** * **Controllable timing:** Allows precise control over the delay duration. * **Flexible device targeting:** Can target different devices by modifying the `ka_cnt` variable. * **Manageable delay generation:** Provides flexibility and control over the injected delay. * **Reduces testing overhead:** Minimizes need for manual device configuration. **Important notes:** * The script requires root privileges to execute. * The delay duration should be within the range of a few seconds to a few minutes. * Ensure your systemtap version is high enough to utilize the `udelay` function. **Overall, this article demonstrates the power of `systemtap` and its ability to simulate hardware I/O jitter for performance testing.**

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