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    Subject[RFC PATCH 0/2] kbuild: Cache exploratory calls to the compiler
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    This two-patch series attempts to speed incremental builds of the
    kernel up by a bit. How much of a speedup you get depends a lot on
    your environment, specifically the speed of your workstation and how
    fast it takes to invoke the compiler.

    In the Chrome OS build environment you get a really big win. For an
    incremental build (via emerge) I measured a speedup from ~1 minute to
    ~35 seconds. ...but Chrome OS calls the compiler through a number of
    wrapper scripts and also calls the kernel make at least twice for an
    emerge (during compile stage and install stage), so it's a bit of a
    worst case.

    Perhaps a more realistic measure of the speedup others might see is
    running "time make help > /dev/null" outside of the Chrome OS build
    environment on my system. When I do this I see that it took more than
    1.0 seconds before and less than 0.2 seconds after. So presumably
    this has the ability to shave ~0.8 seconds off an incremental build
    for most folks out there. While 0.8 seconds savings isn't huge, it
    does make incremental builds feel a lot snappier.

    Please note that I make no illusions of being a Makefile expert nor do
    I have any belief that I fully understand the Linux kernel build
    system. Please take this patch series as the start of a discussion
    about whether others feel like this type of speedup is worthwhile and
    how to best accomplish it. Specific things to note:

    - I'm happy to paint the bikeshed any color that maintainers want. If
    you'd like the cache named differently, in a slightly different
    format, or you want me to adjust the spacing / names of Makefile
    stuff then please just let me know.

    - If this is totally the wrong approach and you have a better idea
    then let me know. If you want something that's super complicated to
    explain then feel free to post a replacement patch and I'm happy to
    test.

    - This patch definitely needs extra testing. I've tested it on a very
    limited build environment and it seems to be working fine, but I
    could believe that with some weird compiler options or on certain
    architectures you might need some extra escaping here and there.


    Douglas Anderson (2):
    kbuild: Add a cache for generated variables
    kbuild: Cache a few more calls to the compiler

    Documentation/kbuild/makefiles.txt | 21 ++++++
    Makefile | 9 ++-
    scripts/Kbuild.include | 133 +++++++++++++++++++++++++++++++------
    3 files changed, 142 insertions(+), 21 deletions(-)

    --
    2.14.1.821.g8fa685d3b7-goog

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