Re: [GIT PULL] RCU updates for v5.1

From: Ingo Molnar
Date: Wed Mar 06 2019 - 02:08:43 EST

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Tue, Mar 5, 2019 at 4:03 AM Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> >
> > Please pull the latest core-rcu-for-linus git tree from:
> >
> > git:// core-rcu-for-linus
> Hmm. I think this made my build time explode.
> I'm bisecting, but it looks like my allmodconfig builds went from ~31
> min to ~39 min with this pull.
> NOTE! I'm not saying that the kernel slowed down. Just the *build*
> (with the same kernel) slowed down.
> It's odd, and maybe I did something wrong, so I'll have to
> double-check the numbers, but I thought I'd mention it in case
> somebody goes "Ahh, I did X to the include files, so now every
> compiler invocation probably sees all of xyz and that will slow things
> down enormously".

Could it be the locking tree?

In particular the atomics auto-generation slowed down the build before,
but this build regression was thought to be fixed with:

0cf264b3133d: locking/atomics: Check atomic headers with sha1sum

but maybe that's not the whole story?

Or it's an unreported slowdown related to the RCU tree, as you say.