linux-kernel - Re: Question re: building with cp -l (hard linked sources)

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Date:   Sun, 20 Nov 2022 19:42:49 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: Question re: building with cp -l (hard linked sources)

On 11/20/22 12:58, Mirsad Goran Todorovac wrote:
> Hi, Mr. Bagas,
> 
> I am in process of bisecting another bug. Right now I take about 1h30m to build both
> the good and bad version of a kernel in bisection.
> 
> It helped a great deal to do the following:
> 
> # time rm -rf linux_stable_build
> # time cp -rp -l linux_stable linux_stable_build
> # time diff -ur linux_stable linux_stable_build
> # cd linux_stable_build
> # rm .config
> # cp /boot/config-EXAMPLE .config
> # time nice make CC="ccache gcc" KBUILD_BUILD_TIMESTAMP="" -j20 bindeb-pkg |& tee ../error-${VER}.log
> 
> I've been doing the good and bad bisect build in the same directory, but is seems to me that
> ccache then doesn't realise it compiles the same source twice?
> 
> I am not certai of the reliability of a build in a directory with hard links to the original local git
> repo copy? How does it handle git checkouts and git bisect resets? Is it supported?
> 
> I am asking because I haven't found an answer in any available man pages, and the build and git checkout
> process is rather obscure.
> 
> It seems to me that build in directory with hard link instead of copying is much faster, and I could
> do simultaneous bad and good bisect build, for only one source file has to be fetched and loaded from
> the disk into the cache and memory.
> 
> However, I cannot test that while bisecting, for it might interfere with some other fault in the tested
> kernel.
> 
> Is it supported to bisection build in the same directory where the source is? And then do a make mrproper?
> 
> I don't know how git and ccache interoperate?
> 
> Any advice?
> 
> The current procedure works, but it is not time efficient (15 steps might take 30 hours).
> 

You may want to see ccache(1), especially "COMPILING IN DIFFERENT DIRECTORIES"
section.

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