Re: [GIT pull] perf/urgent for 5.7-rc2

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [GIT pull] perf/urgent for 5.7-rc2
Date: Mon, 20 Apr 2020 09:51:55 -0700	[thread overview]
Message-ID: <CAHk-=wiG=Bz57AUmbTyZYMKU6C+nZpS8P2=vFf5xAAhBzrPuTQ@mail.gmail.com> (raw)
In-Reply-To: <20200420074845.GA72554@gmail.com>

On Mon, Apr 20, 2020 at 12:48 AM Ingo Molnar <mingo@kernel.org> wrote:
>
> Fortunately, much of what objtool does against vmlinux.o can be
> parallelized in a rather straightforward fashion I believe, if we build
> with -ffunction-sections.

Well, I was actually thinking about a simpler model.

By "link time" I didn't mean "after final link". Yes, there may be
reasons to do it at that point too (to do any whole-program checks),
but that wasn't what I meant.

I meant literally doing it in the $(LD) and $(AR) phases, when you
still have lots of independent object files that you are just about to
link (or archive - do we even do that any more?) into one.

Then you'd parallelize exactly the same way we do now: one object file
at a time, and with no real change of semantics.

IOW, what I was thinking that instead of doing it as part of a final
step after the CC/AS, we'd do it as a preparatory step before the
LD/AR. Same exact operation, same exact target *.o files, just shifted
in time.

             Linus