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Date:   Sun, 15 Oct 2017 16:48:40 +0900
From:   Masahiro Yamada <>
To:     Douglas Anderson <>
Cc:     Guenter Roeck <>,
        Simon Glass <>,
        Brian Norris <>,
        Ingo Molnar <>,
        Matthias Kaehlcke <>,
        Cao jin <>,
        Arnd Bergmann <>, James Hogan <>,
        Linux Kbuild mailing list <>,
        Michal Marek <>,
        Linux Kernel Mailing List <>,
        Mark Charlebois <>
Subject: Re: [PATCH v3 0/2] kbuild: Cache exploratory calls to the compiler

2017-10-12 1:19 GMT+09:00 Douglas Anderson <>:
> 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.
> Ingo Molnar also did some testing of this in his environment and found
> that an incremental build of his subsystem sped up from ~.44 seconds
> before to ~.15 seconds after.  Clean builds also sped up by a marginal
> amount.  :)
> Changes in v3:
> - Rule to prevent make from trying to generate the cache
> - Rule to clean
> - No more doc changes
> - Moved cache stuff below cc-cross-prefix
> - Removed duplicate documentation of try-run (oops)
> - Add Tested-by for Ingo and Guenter since v2 and v3 are very similar
> Changes in v2:
> - Abstract at a different level (like shell-cached) per Masahiro Yamada
> - Include ld-version, which I missed the first time
> Douglas Anderson (2):
>   kbuild: Add a cache for generated variables
>   kbuild: Cache a few more calls to the compiler
>  Makefile               |  5 +--
>  scripts/Kbuild.include | 87 ++++++++++++++++++++++++++++++++++++++++++--------
>  2 files changed, 76 insertions(+), 16 deletions(-)

Series, applied to linux-kbuild/kbuild.

Best Regards
Masahiro Yamada

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