Re: [PATCH 00/23] kbuild: significantly speed up kernel builds

[Linus Torvalds]

On Tue, 8 Sept 2026 at 13:55, Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx> wrote:
>
> A typical kernel build consists of a frustratingly large amount of time

.. you're preaching to the choir.

>                 == allmodconfig FULL build ==
>
>                         before    after     delta
>                       ----------------------------------
> Threadripper, gcc       345.3s   275.2s    -70.1s (-20%)

Well, that's certainly very encouraging. We should do this. I sent out
some emails as just reactions to individual patches, but I have no
numbers to back any of those emails up, and I never actually applied
this series to my tree - they were all based on reading the patches
themselves.

That said:

> An LLM was used to first determine where the bottlenecks were then to
> figure out how to improve them.
>
> It generated a lot of code, much of it hideous.

This made me scared to look at the patches originally, and I held off
in fear that the patches would be horrible and this build time
improvement would be hugely controversial garbage code.

But:

> I extensively audited and rewrote a lot of it, and heavily edited commit
> messages, the cover letter and comments.

None of the patches look at all horrible to me. You clearly excised
the hideous parts. All of my reactions were of the type "this could
probably be taken _further_" rather than me throwing my hands up in
disgust.

So the Rust parallelism thing clearly isn't ready based on feedback
from that quarter, but the rest looked safe and innocuous. I'm all for
merging this, although it should obviously go in through the right
channels. Mostly the kbuild tree, although some of it clearly would be
other cases - the objtool change in particular is fairly substantial
and needsobjtool people to approve. It didn't look all that
contentious, but still..

Anyway, I'd love for this all to go in. Build times are a pet peeve of mine.

              Linus