Linux Kernel Module Cheat

26.2.1. Enable Buildroot compiler optimizations

If you are benchmarking compiled programs instead of hand written assembly, remember that we configure Buildroot to disable optimizations by default with:

BR2_OPTIMIZE_0=y

to improve the debugging experience.

You will likely want to change that to:

BR2_OPTIMIZE_3=y

Our buildroot_packages/sample_package package correctly forwards the Buildroot options to the build with $(TARGET_CONFIGURE_OPTS), so you don’t have to do any extra work.

Don’t forget to do that if you are adding a new package with your own build system.

Then, you have two choices:

if you already have a full -O0 build, you can choose to rebuild just your package of interest to save some time as described at: Section 26.2, “Custom Buildroot configs”
```
./build-buildroot \
  --config 'BR2_OPTIMIZE_3=y' \
  --config 'BR2_PACKAGE_SAMPLE_PACKAGE=y' \
  -- \
  sample_package-dirclean \
  sample_package-reconfigure \
;
```
However, this approach might not be representative since calls to an unoptimized libc and other libraries will have a negative performance impact.

Maybe you can get away with rebuilding libc, but I’m not sure that it will work properly.

Kernel-wise it should be fine though as mentioned at: Section 3.1.2, “Disable kernel compiler optimizations”

clean the build and rebuild from scratch:

mv out out~
./build-buildroot --config 'BR2_OPTIMIZE_3=y'