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Profiling the Linux kernel

If you do not include the kernel in the images in the Capture & Analysis Options dialog box, the statistics generated by the kernel are not aligned with source code in the Analysis Reports. Before you can include the Linux kernel in the Program Images section of the Capture & Analysis Options dialog, you must build a version of vmlinux with kernel debug information enabled.

To profile the Linux kernel, follow these steps:

Procedure

  1. Navigate to the kernel build directory.
  2. Enter the following command to enable you to change menuconfig options:

    make ARCH=arm CROSS_COMPILE=<cross_compiler_directory>/bin/arm-linux-gnueabihf- menuconfig

  3. In the Kernel Hacking menu, select the Compile the kernel with debug info option. This enables the CONFIG_DEBUG_INFO kernel option.
    The options described in  Required kernel configuration menu options must also be enabled.
  4. Enter the following command to build the image:

    make -j5 ARCH=arm CROSS_COMPILE=<cross_compiler_directory>/bin/arm-linux-gnueabihf- uImage

    This creates a new vmlinux image.

    Note

    You can profile a driver by either statically linking it into the kernel image or by adding the module as an image in the Capture & Analysis Options dialog box.
  5. Optional: Enable kernel stack unwinding using either of the following methods:
    • Remove the comment tags that surround GATOR_KERNEL_STACK_UNWINDING in the Makefile and rebuild gator.ko.

    • Run the following command as root on the target after gatord has started:

      echo 1 > /sys/module/gator/parameters/kernel_stack_unwinding

    Note

    • This step is only required if you previously built gator.ko with kernel stack unwinding turned off.

    • Enabling kernel stack unwinding might trigger errors that appear at millisecond intervals during the capture session. If you experience this behavior, disable kernel stack unwinding.

  6. Open the Capture & Analysis Options dialog box.
  7. Click the Add ELF image... button in the Program Images section.
  8. Navigate to your vmlinux file and select it.
  9. Click OK
  10. Start a new capture session.
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