linux-kernel - Re: [GIT] kbuild/lto changes for 3.15-rc1

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Message-ID: <CA+55aFzhyvZRPjXy7PkUxQO_AMqLSTehh-GNRP+Dx3yKnv-eCA@mail.gmail.com>
Date:	Tue, 8 Apr 2014 15:44:25 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Michal Marek <mmarek@...e.cz>, Andi Kleen <ak@...ux.intel.com>,
	Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT] kbuild/lto changes for 3.15-rc1

On Tue, Apr 8, 2014 at 1:49 PM,  <josh@...htriplett.org> wrote:
>
> In addition to making the kernel smaller and such (I'll leave the
> specific stats there to Andi), here's the key awesomeness of LTO that
> you, personally, should find useful and compelling: LTO will eliminate
> the need to add many lower-level Kconfig symbols to compile out bits of
> the kernel.

Actually that, to me, is a negative right now.

Since there's no way we'll make LTO the default in the foreseeable
future, people starting to use it like that is just a bad bad thing.

So really, the main advantage of LTO would be any actual optimizations
it can do. And call me anal, but I want *numbers* for that before I
merge it. Not handwaving. I'm not actually aware of how well - if at
all - code generation actually improves.

                Linus
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