linux-kernel - Re: [PATCH] gen_compile_command: Add support for separate KBUILD

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Message-ID: <20190620203845.GA102280@archlinux-epyc>
Date:   Thu, 20 Jun 2019 13:38:45 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Doug Anderson <dianders@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Tom Roeder <tmroeder@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Raul E Rangel <rrangel@...omium.org>,
        Tom Hughes <tomhughes@...omium.org>,
        Ryan Case <ryandcase@...omium.org>, Yu Liu <yudiliu@...gle.com>
Subject: Re: [PATCH] gen_compile_command: Add support for separate
 KBUILD_OUTPUT directory

On Thu, Jun 20, 2019 at 01:25:36PM -0700, Nick Desaulniers wrote:
> On Thu, Jun 20, 2019 at 1:13 PM Doug Anderson <dianders@...gle.com> wrote:
> > On Thu, Jun 20, 2019 at 12:53 PM Nick Desaulniers
> > <ndesaulniers@...gle.com> wrote:
> > >
> > > I do miss Doug's Kbuild caching patches' speedup.
> >
> > You actually get quite a bit of this by grabbing a new version of
> > ccache (assuming you use ccache).  :-P  You still have to pay the
> > penalty (twice) for all the options that are tested that the compiler
> > _doesn't_ support, but at least you get the cache for the commands
> > that the compiler does support.
> 
> Hello darkness my old friend:
> https://nickdesaulniers.github.io/blog/2018/06/02/speeding-up-linux-kernel-builds-with-ccache/
> Man, that post has not aged well.  Here's what we do now:
> https://github.com/ClangBuiltLinux/continuous-integration/blob/45ab5842a69cb0c72d27d34e73b0599ec2a0e2ed/driver.sh#L227-L245
> 
> > Specifically, make sure you have a ccache with:
> >
> >     * https://github.com/ccache/ccache/pull/365
> >     * https://github.com/ccache/ccache/pull/370
> 
> Oh! Interesting finds and thanks for the pointers.  Did these make it
> into a release version of ccache, yet? If so, do you know which
> version?
>

It should be available in 3.7 if I am reading git history right.

Cheers,
Nathan

> > I still have it in my thoughts to avoid the penalty for options that
> > the compiler doesn't support but haven't had time to work on it
> > recently.
> 
> It had better not be autoconf! (Hopefully yet-to-be-written GNU C
> extensions can support feature detection via C preprocessor)
> -- 
> Thanks,
> ~Nick Desaulniers