linux-kernel - Re: [PATCH v5 0/2] kbuild: distributed build support for Clang ThinLTO

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Message-ID: <CAF1bQ=RvJnN2DULkRPk7LBK07HsRaON5fMbny1ZmpjuO8cvvOQ@mail.gmail.com>
Date: Thu, 4 Dec 2025 10:36:36 -0800
From: Rong Xu <xur@...gle.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nicolas Schier <nicolas.schier@...ux.dev>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Alice Ryhl <aliceryhl@...gle.com>, 
	Sami Tolvanen <samitolvanen@...gle.com>, "Mike Rapoport (Microsoft)" <rppt@...nel.org>, 
	Rafael Aquini <aquini@...hat.com>, Michael Ellerman <mpe@...erman.id.au>, 
	Stafford Horne <shorne@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	Piotr Gorski <piotrgorski@...hyos.org>, Teresa Johnson <tejohnson@...gle.com>, 
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH v5 0/2] kbuild: distributed build support for Clang ThinLTO

Thanks Nathan for testing and reviewing the patch!

On Thu, Dec 4, 2025 at 9:50 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Hi Rong,
>
> On Tue, Oct 28, 2025 at 06:28:20PM +0000, xur@...gle.com wrote:
>
> First of all, my apologies for taking so long to get to testing and
> reviewing this patchset.
>
> > Rong Xu (2):
> >   kbuild: move vmlinux.a build rule to scripts/Makefile.vmlinux_a
> >   kbuild: distributed build support for Clang ThinLTO
> >
> >  .gitignore                 |  2 +
> >  Makefile                   | 25 +++++-------
> >  arch/Kconfig               | 19 +++++++++
> >  scripts/Makefile.lib       |  7 ++++
> >  scripts/Makefile.thinlto   | 40 ++++++++++++++++++
> >  scripts/Makefile.vmlinux_a | 83 ++++++++++++++++++++++++++++++++++++++
> >  scripts/mod/modpost.c      | 15 +++++--
> >  7 files changed, 174 insertions(+), 17 deletions(-)
> >  create mode 100644 scripts/Makefile.thinlto
> >  create mode 100644 scripts/Makefile.vmlinux_a
>
> Overall, this seems reasonable from a high level perspective. I have
> been testing it with my arm64 and x86_64 distribution configurations for
> the past couple of days and I have not noticed any issues.
>
> Did you take a look at the robot report from patch 2?
>
>   https://lore.kernel.org/202511052257.Bb85ptQG-lkp@intel.com/
>
> It seems like it could be caused by different optimizations?

I haven't tried to reproduce the issue in this report. However, based
on the warning messages, it looks fine to me: Distributed build mode
will have different optimizations from current in-process ThinLTO
build. This is mainly due to the fact that distributed build mode has
more precise option control. For a more detailed explanation, please
refer to my LLVM Discourse post:
https://discourse.llvm.org/t/rfc-distributed-thinlto-build-for-kernel/85934

Additionally, I will be presenting a talk on distributed ThinLTO
builds at the LPC next week and would be happy to discuss this topic
further with interested individuals in person.

Thanks,

-Rong

>
> I plan to take a more in-depth look at the implementation after I am
> back home from Plumbers in a couple of weeks (just to make sure I
> understand it from a maintainer's perspective). Based on that, I will
> either apply it to kbuild-next for 6.20/7.0 or ask for further
> interations, while still aiming to get it into that release.
>
> Cheers,
> Natha