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 allowsperf
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.
Frequently Asked Question
Are you stuck with Perf on Arm Cortex-A7 producing no callstacks? Worry not, we’ve got you covered!
What is the main reason why Perf on Arm Cortex-A7 produces no callstacks?
The main reason why Perf on Arm Cortex-A7 produces no callstacks is because the Cortex-A7 does not support the last branch record (LBR) feature, which is required for generating callstacks.
Is there a workaround to get callstacks on Arm Cortex-A7?
Yes, you can use the –call-graph=dwarf option with Perf to generate callstacks using the Dwarf unwinder. This method does not require LBR support and can provide some level of callstack information.
What is the impact of not having callstacks on the debugging process?
Not having callstacks can make it more difficult to identify the root cause of performance issues or bugs, as you won’t have a clear picture of the program’s execution path. This can lead to longer debugging times and potentially more errors.
Can I use other profiling tools to get callstacks on Arm Cortex-A7?
Yes, you can use other profiling tools like OProfile or Arm’s own Streamline profiler, which may provide alternative methods for generating callstacks on Arm Cortex-A7. However, these tools may have their own limitations and requirements.
Are there any hardware or software modifications that can enable LBR on Arm Cortex-A7?
Unfortunately, it’s not possible to enable LBR on Arm Cortex-A7 through software modifications or firmware updates, as LBR is a hardware feature that requires specific silicon support. You may need to consider using a different processor or platform that supports LBR.