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    SubjectRe: [PATCH] Makefile: support compressed debug info
    On Tue, May 12, 2020 at 9:23 PM Nick Desaulniers
    <ndesaulniers@google.com> wrote:
    >
    > On Mon, May 11, 2020 at 10:54 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
    > >
    > > > >On Mon, May 4, 2020 at 5:13 AM Nick Desaulniers
    > > > ><nick.desaulniers@gmail.com> wrote:
    > > > >>
    > > > >> As debug information gets larger and larger, it helps significantly save
    > > > >> the size of vmlinux images to compress the information in the debug
    > > > >> information sections. Note: this debug info is typically split off from
    > > > >> the final compressed kernel image, which is why vmlinux is what's used
    > > > >> in conjunction with GDB. Minimizing the debug info size should have no
    > > > >> impact on boot times, or final compressed kernel image size.
    > > > >>
    > > Nick,
    > >
    > > I am OK with this patch.
    > >
    > > Fangrui provided the minimal requirement for
    > > --compress-debug-sections=zlib
    > >
    > >
    > > Is it worth recording in the help text?
    > > Do you want to send v2?
    >
    > Yes I'd like to record that information. I can also record Sedat's
    > Tested-by tag. Thank you for testing Sedat.
    >
    > I don't know what "linux-image-dbg file" are, or why they would be
    > bigger. The size of the debug info is the primary concern with this
    > config. It sounds like however that file is created might be
    > problematic.
    >

    Hi Nick,

    sorry, I try to explain the magic of "linux-image-dbg file".

    In my workflow, I use the "scripts/package/{builddeb,mkdebian}"
    shipped with the Linux-kernel as a base to build my Debian packages.

    With enabled debugging (CONFIG_DEBUG_INFO=y) a
    "linux-image-$KERNELRELEASE-dbg" Debian package is created.

    [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/package/mkdebian#n203

    As you can see below...

    [ CONFIG_DEBUG_INFO_COMPRESSED=n ]

    47 5.7.0-rc4-1-amd64-clang/linux-image-5.7.0-rc4-1-amd64-clang_5.7.0~rc4-1~bullseye+dileks1_amd64.deb
    424 5.7.0-rc4-1-amd64-clang/linux-image-5.7.0-rc4-1-amd64-clang-dbg_5.7.0~rc4-1~bullseye+dileks1_amd64.deb

    [ CONFIG_DEBUG_INFO_COMPRESSED=y ]

    47 5.7.0-rc4-2-amd64-clang/linux-image-5.7.0-rc4-2-amd64-clang_5.7.0~rc4-2~bullseye+dileks1_amd64.deb
    771 5.7.0-rc4-2-amd64-clang/linux-image-5.7.0-rc4-2-amd64-clang-dbg_5.7.0~rc4-2~bullseye+dileks1_amd64.deb

    ...there is minimal change in the size for the Debian package w/o
    debug-infos - approx. 47M.
    As said 424M vs. 771M for the dbg packages.

    There is another big benefit checking my recorded stats:

    $ grep 'cache size' stats/5.7.0-rc4-*/ccache-s.txt
    stats/5.7.0-rc4-1-amd64-clang/ccache-s.txt:cache size
    4.7 GB
    stats/5.7.0-rc4-1-amd64-clang/ccache-s.txt:max cache size
    10.0 GB
    stats/5.7.0-rc4-2-amd64-clang/ccache-s.txt:cache size
    3.4 GB
    stats/5.7.0-rc4-2-amd64-clang/ccache-s.txt:max cache size
    10.0 GB

    So the cache of ccache is reduced: 4.7 GB vs. 3.4 GB

    If you have any questions, "Don't ask to ask - just ask." :-).

    Thanks.

    Regards,
    - Sedat -

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