linux-kernel - Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

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Date:	Thu, 8 Jan 2009 22:00:28 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	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>,
	Matthew Wilcox <matthew@....cx>,
	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>
Subject: Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

On Fri, 9 Jan 2009 04:35:31 +0100 Andi Kleen <andi@...stfloor.org> wrote:

> On Thu, Jan 08, 2009 at 05:44:25PM -0800, H. Peter Anvin wrote:
> > Harvey Harrison wrote:
> > >>
> > >> We might still try the second or third options, as i think we shouldnt go 
> > >> back into the business of managing the inline attributes of ~100,000 
> > >> kernel functions.
> > > 
> > > Or just make it clear that inline shouldn't (unless for a very good reason)
> > > _ever_ be used in a .c file.
> > > 
> > 
> > The question is if that would produce acceptable quality code.  In
> > theory it should, but I'm more than wondering if it really will.
> 
> I actually often use noinline when developing code simply because it 
> makes it easier to read oopses when gcc doesn't inline ever static
> (which it normally does if it only has a single caller). You know
> roughly where it crashed without having to decode the line number.
> 
> I believe others do that too, I notice it's all over btrfs for example.
> 

Plus there is the problem where

foo()
{
	char a[1000];
}

bar()
{
	char a[1000];
}

zot()
{
	foo();
	bar();
}

uses 2000 bytes of stack.

Fortunately scripts/checkstack.pl can find these.

If someone runs it.

With the right kconfig settings.

And with the right compiler version.
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