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

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Message-ID: <20090109094142.367012b6@infradead.org>
Date:	Fri, 9 Jan 2009 09:41:42 -0800
From:	Dirk Hohndel <hohndel@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Matthew Wilcox <matthew@....cx>, Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	jim owens <jowens@...com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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

On Fri, 9 Jan 2009 18:47:19 +0100
Andi Kleen <andi@...stfloor.org> wrote:

> On Fri, Jan 09, 2009 at 10:28:01AM -0700, Matthew Wilcox wrote:
> > On Fri, Jan 09, 2009 at 06:20:11PM +0100, Andi Kleen wrote:
> > > Also cc Honza in case he has comments (you might want
> > > to review more of the thread in the archives) 
> > 
> > I think this particular bug is already known and discussed:
> 
> I thought so initially too, but:
> 
> > 
> > http://gcc.gnu.org/ml/gcc/2008-12/msg00365.html
> > 
> > and it hints at being fixed with gcc 4.4.  Does anyone want to test
> > that?
> 
> Hugh already tested with 4.4 and it didn't work well. At least
> a lot of the low level asm inlines were not inlined.
> So it looks like it's still mistuned for the kernel.

I think that's the point. gcc will not get it right. 
So we need to do it ourselves in the kernel sources.
We may not like it, but it's the only way to guarantee reproducable
reliable inline / noinline decisions.

/D

-- 
Dirk Hohndel
Intel Open Source Technology Center
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