linux-kernel - Re: [PATCH v2 0/2] kbuild: Cache exploratory calls to the compiler

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Date:   Wed, 4 Oct 2017 18:46:03 -0700
From:   Guenter Roeck <groeck@...gle.com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <mmarek@...e.com>,
        Guenter Roeck <groeck@...omium.org>, sjg@...omium.org,
        Brian Norris <briannorris@...omium.org>,
        Marcin Nowakowski <marcin.nowakowski@...tec.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Charlebois <charlebm@...il.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        James Hogan <james.hogan@...tec.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2 0/2] kbuild: Cache exploratory calls to the compiler

On Wed, Oct 4, 2017 at 3:37 PM, Douglas Anderson <dianders@...omium.org> wrote:
> 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.
>
> Caveats from v1 still copied here, though with Masahiro Yamada's
> suggestions from v1 this is starting to feel a little more baked and
> I've even dropped the RFC from it (though extra testing still
> appreciated):
>
> 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.
>

Not being a makefile expert, I can't say anything about the merits of
this series. However, it does pass a run on my test farm at
kerneltests.org. So. I'll give it a

Tested-by: Guenter Roeck <linux@...ck-us.net>

Guenter

> 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
>
>  Documentation/kbuild/makefiles.txt | 21 +++++++++
>  Makefile                           |  4 +-
>  scripts/Kbuild.include             | 90 ++++++++++++++++++++++++++++++++------
>  3 files changed, 99 insertions(+), 16 deletions(-)
>
> --
> 2.14.2.920.gcf0c67979c-goog
>