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Date: Sun, 27 Jan 2013 13:49:42 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/asm] x86/defconfig: Turn on
 CONFIG_CC_OPTIMIZE_FOR_SIZE= y in the 64-bit defconfig
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* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Sat, 2013-01-26 at 11:43 -0800, Linus Torvalds wrote:
> 
> > The problem, of course, is that most -O2 code generation is done
> > assuming hot loops that don't show much if any I$ issues. And the -Os
> > thing is done *purely* for size, not taking any performance into
> > account at all. There's no balanced middle ground, which is what _we_
> > would want.
> 
> Gcc needs to implement a -Olinus

What we really want is a sane default for 'library code' 
optimization:

 - cache-cold optimizations for run-through-once non-looping 
   code (-Os)

 - good loop optimizations for anything that arguably loops (-O2)

 - plus common-sense fixes to -Os like not throwing away 
   explicit branch hints we go to great pains to insert.

Possibly some time this decade.

Thanks,

	Ingo