The Mysterious Case of “perf on arm cortex-a7 produces no callstacks”: A Step-by-Step Guide to Troubleshooting

Are you frustrated by the lack of callstacks when running perf on an Arm Cortex-A7 processor? You’re not alone! In this comprehensive guide, we’ll delve into the possible causes and provide clear, actionable steps to help you troubleshoot and resolve this issue.

Understanding the Problem

The perf command is a powerful tool for performance analysis, but it relies on certain system configurations and kernel versions to function correctly. When running perf on an Arm Cortex-A7 processor, you might encounter an issue where no callstacks are produced, leaving you wondering what’s going on.

Possible Causes of the Issue

• Incompatible Kernel Version: Older kernel versions might not support the necessary features for perf to generate callstacks.
• Incorrect System Configuration: Misconfigured system settings, such as kernel parameters or boot arguments, can prevent perf from functioning correctly.
• Hardware Limitations: The Arm Cortex-A7 processor might have architectural limitations that restrict the ability to collect callstacks.
• perf Command Options: Incorrect or missing command-line options can prevent perf from generating callstacks.

Step-by-Step Troubleshooting Guide

Let’s dive into the detailed troubleshooting process to help you identify and fix the issue.

Step 1: Verify the Kernel Version

Check the kernel version using the following command:

uname -a

Ensure that the kernel version is at least 3.14 or later, as earlier versions might not support the necessary features for perf to generate callstacks.

Step 2: Configure System Settings

Verify that the following system settings are correctly configured:

• Kernel Parameters: Ensure that the perf_event_paranoid kernel parameter is set to a value that allows perf to collect callstacks. You can check the current value using:

  cat /proc/sys/kernel/perf_event_paranoid

  Set the value to 1 or 2 using:

  echo 1 | sudo tee /proc/sys/kernel/perf_event_paranoid

• Boot Arguments: Verify that the perf kernel command-line argument is present in the boot arguments. You can check the current boot arguments using:

  cat /proc/cmdline

  Add the perf argument to the boot command-line using:

  sudo nano /boot/config.txt

  Add the following line at the end of the file:

  bootargs=perf

  Save and reboot the system.

Step 3: Check Hardware Limitations

Verify that the Arm Cortex-A7 processor is not the bottleneck. Check the processor documentation to ensure that it supports the necessary features for perf to collect callstacks.

Step 4: Verify perf Command Options

Ensure that you’re using the correct perf command options. The most common options for collecting callstacks are:

perf record -g --call-graph dwarf

Make sure to specify the correct event type and options for your specific use case.

Additional Troubleshooting Steps

If the above steps don’t resolve the issue, try the following additional troubleshooting steps:

Check System Logs

Inspect system logs for any errors or warnings related to perf using:

dmesg | grep perf

Check for any errors or warnings that might indicate the cause of the issue.

Verify perf Version

Ensure that you’re using a compatible version of perf. Check the version using:

perf --version

Verify that the version is compatible with your kernel version and system configuration.

Conclusion

Resolving the issue of “perf on arm cortex-a7 produces no callstacks” requires a systematic approach to troubleshooting. By following the steps outlined in this guide, you should be able to identify and fix the underlying cause of the problem. Remember to carefully verify system settings, kernel versions, and perf command options to ensure that they are correctly configured. With patience and persistence, you’ll be able to collect valuable callstacks and optimize your system’s performance.

Resources

For further information and reference, consult the following resources:

• perf documentation: https://perf.wiki.kernel.org/index.php/Main_Page
• Arm Cortex-A7 processor documentation: https://developer.arm.com/documentation/ddi0464/latest
• Linux kernel documentation: https://www.kernel.org/doc/html/latest/

Keyword	Description
perf	A performance analysis tool for Linux systems
Arm Cortex-A7	A processor architecture used in various embedded systems
callstacks	A visual representation of the call sequence of a program
kernel version	The version of the Linux kernel running on the system

By following this comprehensive guide, you’ll be well on your way to resolving the issue of “perf on arm cortex-a7 produces no callstacks” and unlocking the full potential of your system’s performance analysis capabilities.

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