linux-kernel - Re: [patch] measurements, numbers about CONFIG_OPTIMIZE

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Date:	Fri, 09 Jan 2009 11:17:38 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Richard Guenther <richard.guenther@...il.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthew Wilcox <matthew@....cx>,
	Dirk Hohndel <hohndel@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, jim owens <jowens@...com>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	paulmck@...ux.vnet.ibm.com, Gregory Haskins <ghaskins@...ell.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>, jh@...e.cz
Subject: Re: [patch] measurements, numbers about CONFIG_OPTIMIZE_INLINING=y
 impact

Richard Guenther wrote:
> On Fri, Jan 9, 2009 at 8:21 PM, Andi Kleen <andi@...stfloor.org> wrote:
>>> GCC 4.3 should be good in compiling the
>>> kernel with default -Os settings.
>> It's unfortunately not. It doesn't inline a lot of simple asm() inlines
>> for example.
> 
> Reading Ingos posting with the actual numbers states the opposite.
> 

Well, Andi's patch forcing inlining of the bitops chops quite a bit of 
size off the kernel, so there is clearly room for improvement.  From my 
post yesterday:

: voreg 64 ; size o.*/vmlinux
    text    data     bss     dec     hex     filename
57590217 24940519 15560504 98091240 5d8c0e8 o.andi/vmlinux
59421552 24912223 15560504 99894279 5f44407 o.noopt/vmlinux
57700527 24950719 15560504 98211750 5da97a6 o.opty/vmlinux

110 KB of code size reduction by force-inlining the small bitops.

	-hpa
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