reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/bigeasy/staging.git/commit/?id=6b87810731941de437ede9e1c6a6d894ea843cdf
        git remote add bigeasy-staging https://git.kernel.org/pub/scm/linux/kernel/git/bigeasy/staging.git
        git fetch --no-tags bigeasy-staging sched_dl
        git checkout 6b87810731941de437ede9e1c6a6d894ea843cdf
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs