linux-kernel - Re: build reproducibility

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Message-ID: <alpine.DEB.2.22.394.2110172041010.4761@hadrien>
Date:   Sun, 17 Oct 2021 20:42:31 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Randy Dunlap <rdunlap@...radead.org>
cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org
Subject: Re: build reproducibility



On Sun, 17 Oct 2021, Randy Dunlap wrote:

> On 10/17/21 11:12 AM, Julia Lawall wrote:
> > Hello,
> >
> > If I do the following:
> >
> > git clean -dfx
> > cp saved_config .config
> > make olddefconfig && make && make modules_install && make install
> >
> > Should I always end up with the same kernel, regardless of the kernel that
> > is currently running on the machine?
> >
> > I see a large performance difference between Linux 5.10 and all versions
> > afterwards for a particular benchmark.  I am unable to bisect the problem
> > eg between 5.10 and 5.11, because as soon as I come to a kernel that gives
> > the bad performance, all of the kernels that I generate subsequently in
> > the bisecting process (using the above commands) also have the bad
> > performance.
> >
> > It could of course be that I have completely misinterpreted the problem,
> > and it has nothing to do with the kernel.  But I have tested the program a
> > lot when only working on variants of Linux 5.9.  I only start to have
> > problems when I use versions >= 5.11.
>
> Hi,
>
> My "guess" is that this has something to do with the build
> reusing some current file(s) that need to be rebuilt.
> I.e., adding a "make clean" or "make proper" might be needed.

This was my guess too.  But I have the git clean -dfx.  I did a comparison
with make distclean and this does a little more (mostly some files in
tools).

thanks,
julia

>
> I say this only because sometimes I cannot even reproduce
> a build that has errors or warnings unless I prefix it with
> make clean or mrproper. (i.e., nothing to do with booting
> and running the new kernel)
> Even though the .config file has changed and I do
> "make olddefconfig", the same build errors do not show up
> unless I do the clean or mrproper step also.
>
>
> --
> ~Randy
>