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

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Date:	Fri, 09 Jan 2009 11:13:30 -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:
>>
>> But it's also not inconceivable that gcc adds a -fkernel-inlining or
>> similar that changes the parameters if we ask nicely. I suppose
>> actually such a parameter would be useful for far more programs
>> than the kernel.
> 
> I think that the kernel is a perfect target to optimize default -Os behavior for
> (whereas template heavy C++ programs are a target to optimize -O2 for).
> And I think we did a good job in listening to kernel developers if once in
> time they tried to talk to us - GCC 4.3 should be good in compiling the
> kernel with default -Os settings.  We, unfortunately, cannot retroactively
> fix old versions that kernel developers happen to like and still use.
> 

Unfortunately I think there have been a lot of "we can't talk to them" 
on both sides of the kernel-gcc interface, which is incredibly 
unfortunate.  I personally try to at least observe gcc development, 
including monitoring #gcc and knowing enough about gcc internals to 
write a (crappy) port, but I can hardly call myself a gcc expert. 
Still, I am willing to spend some significant time interfacing with 
anyone in the gcc community willing to spend the effort.  I think we can 
do good stuff.

	-hpa
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